Intended audience: System Administrators, Graphics Programmers, Researchers, and others with knowledge of the Linux or Solaris operating systems, OpenGL and GLX, and X windows.

1 Legal Information

This document and all associated illustrations are licensed under the Creative Commons Attribution 2.5 License. Any works which contain material derived from this document must cite The VirtualGL Project as the source of the material and list the current URL for the VirtualGL web-site.

This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit. Further information is contained in LICENSE-OpenSSL.txt, which can be found in the same directory as this documentation.

VirtualGL includes software developed by the FLTK Project.

VirtualGL is licensed under the wxWindows Library License, v3, a derivative of the GNU Lesser General Public License (LGPL).

2 Overview

VirtualGL is an open source package which gives any Unix or Linux remote display software the ability to run OpenGL applications with full 3D hardware acceleration. Some remote display software, such as VNC, lacks the ability to run OpenGL applications entirely. Other remote display software forces OpenGL applications to use a slow software-only OpenGL renderer, to the detriment of performance as well as compatibility. And running OpenGL applications using the traditional remote X-Windows approach causes all of the OpenGL commands and 3D data to be sent over the network to be rendered on the client machine, which is not a tenable proposition unless the data is relatively small and static, unless the network is fast, and unless the OpenGL application is specifically tuned for a remote X-Windows environment.

With VirtualGL, the OpenGL commands and 3D data are instead redirected to a 3D graphics accelerator on the server machine, and only the rendered 3D images are sent to the client machine. VirtualGL thus “virtualizes” 3D graphics hardware, allowing it to be co-located in the “cold room” with compute and storage resources. VirtualGL also allows 3D graphics hardware to be shared among multiple users, and it provides real-time performance on even the most modest of networks. This makes it possible for large, noisy, hot 3D workstations to be replaced with laptops or even thinner clients; but more importantly, it eliminates the workstation and the network as barriers to data size. Users can now visualize gigabytes and gigabytes of data in real time without needing to cache any of the data locally or sit in front of the machine that is rendering the data.

Normally, a 3D Unix OpenGL application would send all of its drawing commands and data, both 2D and 3D, to an X-Windows server, which may be located across the network from the application server. VirtualGL, however, employs a technique called “split rendering” to force the 3D commands from the application to go to a 3D graphics card in the application server. VGL accomplishes this by pre-loading a dynamic shared object (DSO) into the application at run time. This DSO intercepts a handful of GLX, OpenGL, and X11 commands necessary to perform split rendering. Whenever a window is created by the application, VirtualGL creates a corresponding 3D pixel buffer (“Pbuffer”) on the server’s 3D graphics card. Whenever the application requests that an OpenGL rendering context be created on the window, VirtualGL intercepts the request and creates the context in the Pbuffer instead. Whenever the application swaps or flushes the drawing buffer to indicate that it has completed rendering a frame, VirtualGL reads back the Pbuffer and sends the rendered 3D image to the client.

The beauty of this approach is its non-intrusiveness. VirtualGL monitors a few X11 commands and events to determine when windows have been resized, etc., but it does not interfere in any way with the delivery of 2D X11 commands to the X server. For the most part, VGL does not interfere with the delivery of OpenGL commands to the graphics card, either (there are some exceptions, such as its handling of color index rendering.) VGL merely forces the OpenGL commands to be delivered to a server-side graphics card rather than a client-side one. Once the OpenGL rendering context has been established in a server-side Pbuffer, everything (including esoteric OpenGL extensions, fragment/vertex programs, etc.) should “just work.” In most cases, if an application runs locally on a 3D server/workstation, that same application will run remotely from that same server/workstation using VirtualGL. But obviously, if it were always as simple as that, we could all turn out the lights and go home. Most of the time spent developing VirtualGL has been spent working around “stupid application tricks.”

VirtualGL can currently use one of three “image transports” to send rendered 3D images to the client machine:

1. VGL Image Transport (Formerly “Direct Mode”)

The VGL image transport is most often used whenever the X server is located across the network from the application server, for instance if the X server is running on the user’s desktop machine. VirtualGL uses its own protocol on a dedicated TCP socket to send the rendered 3D images to the client machine, and the VirtualGL Client application decodes the images and composites them into the appropriate X window. The VGL transport can either deliver uncompressed images (RGB encoded), or it can compress images in real time using a high-speed JPEG codec. It also supports the delivery of stereo image pairs, which can be reconstructed into a stereo image by the VirtualGL Client.

Figure 2.1: The VGL Image Transport with a Remote X Server

2. X11 Image Transport (Formerly “Raw Mode”)

The X11 image transport simply draws the rendered 3D images into the appropriate X window using XPutImage() and similar X-Windows commands. This is most useful in conjunction with an “X Proxy”, which can be one of any number of Unix remote display applications, such as VNC. These X proxies are essentially “virtual” X servers. They appear to the application to be a normal X server, but they perform X11 rendering to a virtual framebuffer in main memory rather than to a real framebuffer on a graphics card. This allows the X proxy to send only images to the client machine rather than chatty X-Windows rendering commands. When using the X11 transport, VirtualGL does not perform any image compression or encoding itself. It instead relies upon an X proxy to encode and deliver the images to the client(s). Since the use of an X proxy eliminates the need to send X-Windows commands over the network, this is the best means of using VirtualGL over high-latency or low-bandwidth networks. The VirtualGL Project provides an accelerated version of VNC, called “TurboVNC”, which is meant to be used with VirtualGL’s X11 transport, and the combination of the two provides a highly-performant remote 3D solution, even on slow networks. TurboVNC also provides rudimentary collaboration capabilities, allowing multiple users to simultaneously interact with the same 3D application.

Figure 2.2: The X11 Image Transport with an X Proxy

3. Sun Ray Image Transport

The Sun Ray thin client environment from Sun Microsystems consists of an X proxy (the Sun Ray Server Software) and a series of ultra-thin hardware clients that connect to this proxy over a network. It is similar in concept to VNC, in that a virtual X server is created for every user and that only images, not rendering commands, are sent to the client. But unlike VNC, the client is not a piece of software running on a workstation or laptop. The client is a fanless, diskless little box with only a monitor port, USB ports, a network jack, and a smart card slot (used for authentication.)

This environment presents unique challenges to VirtualGL, however. The first challenge is that the Sun Ray clients contain relatively slow CPUs, so they are not fast enough to decompress JPEG in real time. The second challenge is that Sun Ray servers are generally provisioned to handle a lot of simultaneous users, so using VirtualGL’s X11 transport would put undue stress on both the Sun Ray servers and the network on which they reside. Thus, Sun Microsystems designed a plugin for VirtualGL which allows VGL to compress images using a protocol that can be sent directly to the Sun Ray hardware client without having to pass through the Sun Ray server first. Since the plugin uses the proprietary Sun Ray image compression technology, it is currently closed source, but the binary packages can be downloaded for free as part of Sun’s Shared Visualization product, which also includes VirtualGL, TurboVNC, and other goodies.

Figure 2.3: The Sun Ray Image Transport

3 System Requirements

3.1 Linux/x86

3.2 Linux/Itanium

VirtualGL should build and run on Itanium Linux, but it has not been thoroughly tested. Contact us if you encounter any difficulties.

3.3 Solaris/x86

3.4 Solaris/Sparc

3.5 Mac/x86

3.6 Windows

3.7 Additional Requirements for Stereographic Rendering

3.8 Additional Requirements for Transparent Overlays

4 Obtaining and Installing VirtualGL

4.1 Installing VirtualGL on Linux

Installing TurboJPEG

1. Download v1.10 or later of the TurboJPEG RPM package (turbojpeg-{version}.i386.rpm for 32-bit systems or turbojpeg-{version}.x86_64.rpm for 64-bit systems) from the files area of the VirtualGL SourceForge web-site.
   

   The 64-bit RPM provides both 32-bit and 64-bit TurboJPEG libraries.
   
   .tgz packages are provided for users of non-RPM-based Linux distributions. You can use alien to convert these into .deb packages if you prefer.

2. Log in as root, cd to the directory where you downloaded the RPM package, and issue the following command:

   rpm -U turbojpeg*.rpm
   

Installing VirtualGL

1. Download the VirtualGL RPM package (VirtualGL-{version}.i386.rpm for 32-bit systems or VirtualGL-{version}.x86_64.rpm for 64-bit systems) from the files area of the VirtualGL SourceForge web-site.
   

   The 64-bit RPM provides both 32-bit and 64-bit VirtualGL components.

2. Log in as root, cd to the directory where you downloaded the RPM package, and issue the following commands:

   rpm -e VirtualGL
   rpm -i VirtualGL*.rpm
   

4.2 Installing VirtualGL on Solaris

1. Download the VirtualGL Solaris package (SUNWvgl-{version}.pkg.bz2 for Sparc or SUNWvgl-{version}-x86.pkg.bz2 for x86) from the files area of the VirtualGL SourceForge web-site.
   

   Both packages provide both 32-bit and 64-bit VirtualGL components.

2. Log in as root, cd to the directory where you downloaded the package, and issue the following commands:

   pkgrm SUNWvgl
   

   (answer “Y” when prompted.)

   bzip2 -d SUNWvgl-{version}.pkg.bz2
   pkgadd -d SUNWvgl-{version}.pkg
   

   Select the SUNWvgl package (usually option 1) from the menu.

4.3 Installing VirtualGL on Mac (Client Only)

1. Download the VirtualGL Mac disk image (VirtualGL-{version}.dmg) from the files area of the VirtualGL SourceForge web-site.
2. Open the disk image, then open VirtualGL-{version}.pkg inside the disk image. Follow the instructions to install the Mac client. The Mac package installs files in the same locations as the Linux RPM.

4.4 Installing VirtualGL on Windows (Client Only)

1. Download the VirtualGL Windows installer package (VirtualGL-{version}.exe) from the files area of the VirtualGL SourceForge web-site.
2. Run the VirtualGL installer. The installation of VirtualGL should be self-explanatory. The only configuration option is the directory into which you want the files to be installed.

4.5 Installing VirtualGL from Source

If you are using a non-RPM-based distribution of Linux or another platform for which there is not a pre-built VirtualGL binary package available, then log in as root, download the VirtualGL source tarball (VirtualGL-{version}.tar.gz) from the files area of the VirtualGL SourceForge web-site, uncompress it, cd vgl, and read the contents of BUILDING.txt for further instructions on how to build and install VirtualGL from source.

4.6 Obtaining and Installing the Sun Ray Plugin

The VirtualGL Sun Ray plugin is a proprietary add-on developed by Sun Microsystems to integrate VirtualGL with the Sun Ray thin client environment. If you plan to use this functionality, then it is recommended that you download and install the Sun Shared Visualization software. This software package is available as a free download (Sun charges for support), and it includes VirtualGL, TurboVNC, the proprietary Sun Ray plugin, enhanced documentation, and enhancements to N1 GridEngine to allow it to manage VirtualGL jobs across a cluster of 3D servers.

4.7 Uninstalling VirtualGL

Linux

As root, issue the following command:

rpm -e VirtualGL

Solaris

As root, issue the following command:

pkgrm SUNWvgl

Answer “yes” when prompted.

Mac

• Download and install the latest version of OSXPM
• Launch OSXPM
• Click the “Delete Package” button
• Find VirtualGL-{version}.pkg in the list of packages and highlight it
• Click “Delete Selected”
• Enter your password if prompted
• Complain to Apple about the lack of a built-in package uninstaller for OS X

Windows

Use the “Add or Remove Programs” applet in the Control Panel (or the “Programs and Features” applet if you’re running Vista.)

5 Obtaining and Installing TurboVNC

5.1 Installing TurboVNC on Linux

Installing TurboJPEG

1. Download v1.10 or later of the TurboJPEG RPM package (turbojpeg-{version}.i386.rpm for 32-bit systems or turbojpeg-{version}.x86_64.rpm for 64-bit systems) from the files area of the VirtualGL SourceForge web-site.
   

   The 64-bit RPM provides both 32-bit and 64-bit TurboJPEG libraries.
   
   .tgz packages are provided for users of non-RPM-based Linux distributions. You can use alien to convert these into .deb packages if you prefer.

2. Log in as root, cd to the directory where you downloaded the RPM package, and issue the following command:

   rpm -U turbojpeg*.rpm
   

Installing TurboVNC

1. Download the TurboVNC RPM package (turbovnc-{version}.i386.rpm) from the files area of the VirtualGL SourceForge web-site.
   
2. Log in as root, cd to the directory where you downloaded the RPM package, and issue the following command:

   rpm -U turbovnc*.rpm
   

5.2 Installing TurboVNC on Solaris

1. Download the TurboVNC Solaris package (SUNWtvnc-{version}.pkg.bz2 for Sparc or SUNWtvnc-{version}-x86.pkg.bz2 for x86) from the files area of the VirtualGL SourceForge web-site.
   
2. Log in as root, cd to the directory where you downloaded the package, and issue the following commands:

   pkgrm SUNWvgl
   

   (answer “Y” when prompted.)

   bzip2 -d SUNWtvnc-{version}.pkg.bz2
   pkgadd -d SUNWtvnc-{version}.pkg
   

   Select the SUNWtvnc package (usually option 1) from the menu.

5.3 Installing TurboVNC on Mac (Client Only)

1. Download the TurboVNC Mac disk image (TurboVNC-{version}.dmg) from the files area of the VirtualGL SourceForge web-site.
2. Open the disk image, then open TurboVNC-{version}.pkg inside the disk image. Follow the instructions to install the Mac client. The Mac package installs files in the same locations as the Linux RPM.

5.4 Installing TurboVNC on Windows (Client Only)

1. Download the TurboVNC Windows installer package (TurboVNC-{version}.exe) from the files area of the VirtualGL SourceForge web-site.
2. Run the TurboVNC installer. The installation of TurboVNC should be self-explanatory. The only configuration option is the directory into which you want the files to be installed.

5.5 Installing TurboVNC from Source

If you are using a non-RPM-based distribution of Linux or another platform for which there is not a pre-built TurboVNC binary package available, then log in as root, download the TurboVNC source tarball (turbovnc-{version}.tar.gz) from the files area of the VirtualGL SourceForge web-site, uncompress it, cd vnc/vnc_unixsrc, and read the contents of BUILDING.txt for further instructions on how to build and install TurboVNC from source.

5.6 Uninstalling TurboVNC

Linux

As root, issue the following command:

rpm -e turbovnc

Solaris

As root, issue the following command:

pkgrm SUNWtvnc

Answer “yes” when prompted.

Mac

• Download and install the latest version of OSXPM
• Launch OSXPM
• Click the “Delete Package” button
• Find TurboVNC-{version}.pkg in the list of packages and highlight it
• Click “Delete Selected”
• Enter your password if prompted
• Complain to Apple about the lack of a built-in package uninstaller for OS X

Windows

Use the “Add or Remove Programs” applet in the Control Panel (or the “Programs and Features” applet if you’re running Vista.)

6 Configuring a Linux or Solaris Machine as a VirtualGL Server

6.1 GLP: Using VirtualGL Without an X Server

Sun’s OpenGL library for Solaris/Sparc systems has a special extension called “GLP” which allows VirtualGL to directly access a 3D graphics card even if there is no X server running on the card. GLP greatly improves the overall security of the VirtualGL server, since it eliminates the need to grant X server access to VirtualGL users. In addition, GLP makes it easy to assign VirtualGL jobs to any graphics card in a multi-card system.

When using GLP, the architecture of VirtualGL changes as follows:

Figure 6.1: The VGL Image Transport with a Remote X Server and GLP

Figure 6.2: The X11 Image Transport with an X Proxy and GLP

If your system is running Sun OpenGL 1.5 for Solaris/Sparc, it is recommended that you configure it to use GLP:

1. Log in as root.
2. Run

   /opt/VirtualGL/bin/vglserver_config
   

3. Select option 3 (Configure server for use with VirtualGL in GLP mode.)

4. Restrict framebuffer device access to vglusers group (recommended)?
   [Y/n]
   

   Yes

   Only users in the vglusers group can run OpenGL applications on the VirtualGL server (the configuration script will create the vglusers group if it doesn’t already exist.) This limits the possibility that an unauthorized user could snoop the 3D framebuffer device(s) and thus see (or alter) the 3D output of an application running in VirtualGL.

   No

   Any authenticated user can run OpenGL applications on the VirtualGL server. If it is necessary for users outside of the vglusers group to log in locally to the server and run OpenGL applications, then this is probably the best option.

5. If you chose to restrict framebuffer device access to the vglusers group, then edit /etc/group and add root to the vglusers group. If you choose, you can also add additional users to the group at this time. Note that any user you add to vglusers must log out and back in again before their new group permissions take effect.
6. Edit the /etc/dt/config/GraphicsDevices file as necessary. This file contains a list of paths to 3D framebuffer devices (such as /dev/fbs/kfb0, /dev/fbs/jfb0, etc.) that you wish to use with VirtualGL.

Sanity Check

To verify that the system is ready to run VirtualGL, log out of the server, log back into the server using SSh, and execute the following command in the SSh session:

/opt/VirtualGL/bin/glxinfo -d glp

This command should output a list of visuals and complete with no errors.

Using GLP by Default in VirtualGL

If you wish VirtualGL to use GLP by default, then you can add

VGL_DISPLAY=glp
export VGL_DISPLAY

to /etc/profile. This will cause VirtualGL to use the first device specified in /etc/dt/config/GraphicsDevices as the default rendering device. Users can override this default by setting VGL_DISPLAY in one of their startup scripts (such as ~/.profile or ~/.login) or by passing an argument of -d <device> to vglrun when invoking VirtualGL. See Chapter 19 for more details.

6.2 Granting Access to the Server’s X Display

VirtualGL requires access to the server’s 3D graphics card so that it can create off-screen pixel buffers (Pbuffers) and redirect the 3D rendering from applications into these Pbuffers. Unfortunately, accessing a 3D graphics card on Linux and Solaris/x86 systems or on Solaris/Sparc systems without GLP requires going through an X server. On such systems, the only way to share the server’s 3D graphics card among multiple users is to grant those users access to the X server that is running on the 3D graphics card.

It is important to understand the security risks associated with this. Once X display access is granted to a user, there is nothing that would prevent that user from logging keystrokes or reading back images from the X display. Using xauth, one can obtain “untrusted” X authentication keys which prevent such exploits, but unfortunately, those untrusted keys also disallow access to the 3D hardware. So it is necessary to grant full trusted X access to any users that will need to run VirtualGL. Unless you fully trust the users to whom you are granting this access, you should avoid logging in locally to the server’s X display as root unless absolutely necessary.

This section will explain how to configure a VirtualGL server such that selected users can run VirtualGL, even if the server is sitting at the login prompt.

1. Shut down the display manager:

   Linux servers

   init 3
   

   Solaris 10 (and later) servers running GDM

   svcadm disable gdm2-login
   

   Solaris servers running dtlogin

   /etc/init.d/dtlogin stop
   

2. Log in as root from the text console (or remotely using SSh.)
3. Run

   /opt/VirtualGL/bin/vglserver_config
   

4. Select option 1 (Configure server for use with VirtualGL in GLX mode.)

5. Restrict local X server access to vglusers group (recommended)?
   [Y/n]
   

   Yes

   Only users in the vglusers group can use VirtualGL (the configuration script will create the vglusers group if it doesn’t already exist.) This is the most secure option, since it prevents any users outside of the vglusers group from accessing (and thus exploiting) the VirtualGL server’s X display.

   No

   VirtualGL can be used by any user that successfully logs into the VirtualGL server. The X server can also be accessed (and potentially exploited) by any user who is logged into the VirtualGL server. If you choose this option, it is recommended that you also disable the XTEST extension (see below.)

6. Restrict framebuffer device access to vglusers group (recommended)?
   [Y/n]
   

   Yes

   Only users in the vglusers group can run OpenGL applications on the VirtualGL server (the configuration script will create the vglusers group if it doesn’t already exist.) This limits the possibility that an unauthorized user could snoop the 3D framebuffer device(s) and thus see (or alter) the 3D output of an application running in VirtualGL.

   No

   Any authenticated user can run OpenGL applications on the VirtualGL server. If it is necessary for users outside of the vglusers group to log in locally to the server and run OpenGL applications, then this is probably the best option.

7. Disable XTEST extension (recommended)?
   [Y/n]
   

   Yes

   Disabling XTEST will not prevent a user from logging keystrokes or reading images from the X display, but if a user has access to the X display, disabling XTEST will prevent them from inserting keystrokes or mouse events and thus hijacking local X sessions on that display.

   No

   VNC requires XTEST, so if you need to attach a VNC server to the VirtualGL server’s local X display, then it is necessary to answer “No” (and thus leave XTEST enabled.)

8. If you chose to restrict X server or framebuffer device access to the vglusers group, then edit /etc/group and add root to the vglusers group. If you choose, you can also add additional users to the group at this time. Note that any user you add to vglusers must log out and back in again before their new group permissions take effect.
9. Restart the display manager:

   Linux servers

   init 5
   

   Solaris 10 (and later) servers running GDM

   svcadm enable gdm2-login
   

   Solaris servers running dtlogin

   /etc/init.d/dtlogin start
   

Sanity Check

To verify that the system is ready to run VirtualGL, log out of the server, log back into the server using SSh, and execute the following commands in the SSh session:

If you restricted X server access to vglusers

xauth merge /etc/opt/VirtualGL/vgl_xauth_key
xdpyinfo -display :0
/opt/VirtualGL/bin/glxinfo -display :0

NOTE: xauth and xdpyinfo are in /usr/openwin/bin on Solaris systems.

If you did not restrict X server access

xdpyinfo -display :0
/opt/VirtualGL/bin/glxinfo -display :0

Both commands should output a list of visuals and complete with no errors. If you chose to disable the XTEST extension, then check the output of xdpyinfo to verify that XTEST does not show up in the list of extensions.

6.3 SSh Server Configuration

The server’s SSh daemon should have the X11Forwarding option enabled and the UseLogin option disabled. This is configured in sshd_config, the location of which varies depending on your distribution of SSh. Linux and Solaris 10 systems generally keep this in /etc/ssh, whereas Blastwave OpenSSh keeps it in /opt/csw/etc and SunFreeware OpenSSh keeps it in /usr/local/etc.

6.4 Un-Configuring the Server

You can use the vglserver_config script to restore the security settings that were in place before VirtualGL was installed. Option 2 (Unconfigure server for use with VirtualGL in GLX mode) will remove any shared access to the server’s X display and thus prevent VirtualGL from accessing the 3D hardware in that manner. Option 2 will also re-enable the XTEST extension on the server’s X display. Both Option 2 and Option 4 (Unconfigure server for use with VirtualGL in GLP mode) will restore the framebuffer device permissions to their default (by default, only root or the user that is currently logged into the system locally can access the framebuffer devices.)

After selecting Option 2, you must restart the display manager before the changes will take effect.

7 Configuring a Windows Machine as a Client for the VGL Image Transport

1. Install Hummingbird Exceed if it isn’t already installed.
2. Add the Exceed path (example: C:\Program Files\Hummingbird\Connectivity\9.00\Exceed) to the system PATH environment if it isn’t already there.

7.1 Optimizing Exceed

Disabling Pixel Format Conversion (Exceed 2006 and earlier)

1. Load Exceed XConfig (right-click on the Exceed taskbar icon, then select Tools–>Configuration.)
2. Open the “X Server Protocol” applet in XConfig.

   If you are using the “Classic View” mode of XConfig, open the “Protocol” applet instead.

3. In the “X Server Protocol” applet, select the “Protocol” tab and make sure that “Use 32 bits per pixel for true color” is not checked.
   
   
4. Click “Validate and Apply Changes.” If XConfig asks whether you want to perform a server reset, click “Yes.”

Disabling Backing Store

1. Load Exceed XConfig (right-click on the Exceed taskbar icon, then select Tools–>Configuration.)
2. Open the “Other Server Settings” applet in XConfig.

   If you are using the “Classic View” mode of XConfig, open the “Performance” applet instead.

3. Select the “Performance” tab and make sure that “Default Backing Store” is set to “None.”
   
   
4. Click “Validate and Apply Changes.” If XConfig asks whether you want to perform a server reset, click “Yes.”

Enabling MIT-SHM

VirtualGL has the ability to take advantage of the MIT-SHM extension in Hummingbird Exceed to accelerate image drawing on Windows. This can improve the overall performance of the VirtualGL pipeline by as much as 20% in some cases.

The bad news is that this extension is not consistently implemented across all versions of Exceed. In particular, Exceed 8, Exceed 9, and Exceed 2008 require patches to make it work properly. If you are using one of these versions of Exceed, you will need to obtain the following patches from the Hummingbird support site:

No patches should be necessary for Exceed 10, 2006, or 2007.

Next, you need to enable the MIT-SHM extension in Exceed:

1. Load Exceed XConfig (right-click on the Exceed taskbar icon, then select Tools–>Configuration.)
2. Open the “X Server Protocol” applet in XConfig.

   If you are using the “Classic View” mode of XConfig, open the “Protocol” applet instead.

3. Select the “Extensions” tab and make sure that “MIT-SHM” is checked.
   
   
4. Click “Validate and Apply Changes.” If XConfig asks whether you want to perform a server reset, click “Yes.”

   ---

8 Using VirtualGL with the VGL Image Transport

Advantages of the VGL Image Transport

• Seamless windows; every application window appears as a separate window on the user’s desktop
• Supports stereographic and overlay rendering
• Built-in encryption
• Consumes fewer server resources, since the 2D (X11) rendering occurs on the client

Disadvantages of the VGL Image Transport

• The VGL Image Transport is designed to be used with remote X servers, thus it relies on the chatty remote X11 protocol to send the 2D elements of the application’s GUI to the user’s desktop. As a result, the VGL Image Transport is not recommended for use on high-latency networks
• No collaboration features
• Requires purchasing Exceed for use with Windows clients
• The client is not stateless. As with any remote X11 app, if the network connection drops, then the application will exit

8.1 VGL Image Transport with X11 Forwarding

This mode is recommended for use on secure local-area networks. The X11 traffic is encrypted, but the VirtualGL image stream is left unencrypted to maximize performance.

Procedure for Linux/Solaris/Mac Clients

1. Start the X server if it isn’t started already (Mac clients: start the Mac X11 application.)
2. Open a new terminal window (Mac clients: in the X11 application, start a new xterm [Command-N] if one isn’t already started.)
3. In the same terminal/xterm window, open a Secure Shell (SSh) session into the VirtualGL server:

   /opt/VirtualGL/bin/vglconnect {user}@{server}
   

   Replace {user} with your user account name on the VirtualGL server and {server} with the hostname or IP address of that server.
4. In the SSh session, start a 3D application using VirtualGL:

   /opt/VirtualGL/bin/vglrun [vglrun options] {application_executable_or_script} {arguments}
   

   Consult Chapter 19 for more information on vglrun command line options.

Procedure for Windows Clients

1. Start Exceed if it isn’t already started. Hover the mouse pointer over the Exceed taskbar icon and make a note of the display number on which Exceed is listening (Example: “Exceed 0.0 Multiwindow Mode”.)
2. Open a new Command Prompt.
3. In the same Command Prompt window, set the DISPLAY environment variable to match the display on which Exceed is listening. Example:

   set DISPLAY=:0.0
   

   If you only ever plan to use one Exceed session at a time, then you can set the DISPLAY environment variable in your global user environment (Control Panel–>System–>Advanced–>Environment Variables.)

4. Open a Secure Shell (SSh) session into the VirtualGL server:

   cd /d "c:\program files\virtualgl-{version}-{build}"
   vglconnect {user}@{server}
   

   Replace {user} with your user account name on the VirtualGL server and {server} with the hostname or IP address of that server.
5. In the SSh session, start a 3D application using VirtualGL:

   /opt/VirtualGL/bin/vglrun [vglrun options] {application_executable_or_script} {arguments}
   

   Consult Chapter 19 for more information on vglrun command line options.

8.2 VGL Image Transport with a Direct X11 Connection

As with the previous mode, this mode performs optimally on local-area networks. However, it is less secure, since both the X11 traffic and the VGL image stream are unencrypted. This mode is primarily useful in grid environments where you may not know ahead of time which server will execute a VirtualGL job. It is assumed that the “submit host” (the machine into which you connect with SSh) and the “execute hosts” (the machines that will run VirtualGL jobs) share the same home directories and reside in the same domain.

Procedure

The procedure for this mode is identical to the procedure for X11 forwarding, except that you should pass a -x argument to vglconnect when connecting to the server:

/opt/VirtualGL/bin/vglconnect -x {user}@{server}

8.3 VGL Image Transport with SSL Encryption

This mode encrypts the VGL image stream and, when used in conjunction with X11 forwarding, provides a completely secure solution. However, enabling SSL encryption can reduce VirtualGL’s performance by as much as 20% on high-speed networks such as Ethernet.

Procedure

The procedure for this mode is identical to the procedure for X11 forwarding, except that you should pass an argument of +s to vglrun when starting a 3D application using VirtualGL. You can also set the environment variable VGL_SSL to 1 on the VirtualGL server prior to invoking vglrun. (see Chapter 19 for more details.)

8.4 VGL Image Transport with X11 Forwarding and SSh Tunneling

This mode is useful when either the VirtualGL server or the client machine are behind restrictive firewalls and only SSh connections are allowed through. Both the VGL image stream and the X11 traffic are tunneled through the SSh connection, and thus this mode provides a completely secure solution. However, using SSh tunneling can reduce VirtualGL’s performance by anywhere from 20-40% on high-speed networks such as Ethernet.

Procedure

The procedure for this mode is identical to the procedure for X11 forwarding, except that you should pass a -s argument to vglconnect when connecting to the server:

/opt/VirtualGL/bin/vglconnect -s {user}@{server}

vglconnect will make two SSh connections into the server, the first to find an open port on the server and the second to create the secure image tunnels and open the secure shell. If you are not using an SSh agent to create password-less logins, then this mode will require you to enter your password twice.

vglconnect -s can be used to create multi-layered SSh tunnels. For instance, if the VirtualGL server is not directly accessible from the Internet, you can use vglconnect -s to connect to a gateway server, then use vglconnect -s again on the gateway server to connect to the VirtualGL server. Both the X11 and the VGL image traffic will be forwarded from the VirtualGL server through the gateway and to the client.

8.5 VGL Image Transport over Gigabit Networks

When using the VGL image transport over Gigabit Ethernet or faster networks, it may be desirable to disable image compression. This can be accomplished by passing an argument of -c rgb to vglrun or setting the environment variable VGL_COMPRESS to rgb on the VirtualGL server machine. Disabling image compression will reduce VirtualGL’s server and client CPU usage by 50% or more, but the tradeoff is that it will also increase VirtualGL’s network usage by a factor of 10 or more. Thus, disabling image compression is not recommended unless you are using switched Gigabit Ethernet (or faster) infrastructure and have plenty of bandwidth to spare.

8.6 The VirtualGL Client Application: Nuts and Bolts

The VirtualGL Client application receives encoded and/or compressed images on a dedicated TCP socket, decodes and/or decompresses the images, and draws the images into the appropriate X window. In previous versions of VirtualGL, it was necessary to manually start the VirtualGL Client prior to connecting to the server, but the new vglconnect script wraps both vglclient and SSh to greatly simplify the process of creating VGL Image Transport connections. One consequence of this ease of use is that the actual workings of vglclient are hidden from view, which makes it a bit more difficult to see the cause of connection failures and other issues as they happen.

vglconnect invokes vglclient with an argument of -detach, which causes vglclient to completely detach from the console and run as a background daemon. It will remain running silently in the background, accepting VGL Image Transport connections for the X display on which it was started, until the X server is reset or until the vglclient process is explicitly killed. Logging out of the X server will reset the X server and thus kill all vglclient instances that are attached to it. You can also explicitly kill all instances of vglclient running under your user account by invoking

vglclient -kill

(vglclient is in /opt/VirtualGL/bin on Linux/Mac/Solaris systems and in c:\program files\virtualgl-{version}-{build} on Windows systems.)

vglconnect instructs vglclient to redirect all of its console output to a log file named {home}/.vgl/vglconnect-{hostname}-{display}.log, where {home} is the path of the current user’s home directory (%USERPROFILE% on Windows systems), {hostname} is the name of the computer running vglconnect, and {display} is the name of the current X display (read from the DISPLAY environment or passed to vglconnect using the -display argument.) In the event that something goes wrong, this log file is the first place to check.

When vglclient successfully starts on a given X display, it stores its listener port numbers in a pair of root window properties on the X display. If other vglclient instances attempt to start on the same X display, they read the X window properties, determine that another vglclient instance is already running, and exit to allow the first instance to retain control. vglclient will clean up these X properties under most circumstances, even if it is explicitly killed. But under rare circumstances (if sent a SIGKILL signal on Unix, for instance), a vglclient instance may exit uncleanly and leave the X properties set. In these cases, it may be necessary to add an argument of -force to vglconnect the next time you use it. This tells vglconnect to start a new vglclient instance, regardless of whether vglclient thinks that there is already an instance running on this X display. Alternately, you can simply reset your X server to clear the orphaned X window properties.

8.6.1 The VirtualGL Client and Firewalls

To retain compatibility with previous versions of VirtualGL, the first vglclient instance on a given machine will attempt to listen on port 4242 for unencrypted connections and 4243 for SSL connections. If it fails to obtain one of those ports, because another application or another vglclient instance is already using them, then vglclient will try to obtain a free port in the range of 4200-4299. Failing that, it will request a free port from the operating system.

In a nutshell: if you only ever plan to run one X server at a time on your client machine, which means that you’ll only ever need one instance of vglclient at a time, then it is sufficient to open inbound ports 4242 and 4243 in your client machine’s firewall. If you plan to run multiple X servers on your client machine, which means that you will need to run multiple vglclient instances, then you may wish to open ports 4200-4299. Similarly, if you are running vglclient on a multi-user TurboVNC or Sun Ray server that has a firewall, then you may wish to open ports 4200-4299 in the server’s firewall. Opening ports 4200-4299 will accommodate up to 50 separate vglclient instances. More instances than that cannot be accommodated on a firewalled machine, unless the firewall is able to create rules based on application executables instead of listening ports.

Note that it is not necessary to open any inbound ports in the firewall to use the VGL Image Transport with SSh Tunneling.

9 Using VirtualGL with TurboVNC

Referring to Chapter 2, the X11 Image Transport bypasses VirtualGL’s internal image compressor and instead draws the rendered 3D images to an X server using standard X11 drawing commands. Since this results in the images being sent uncompressed to the X server, the X11 Image Transport is designed to be used with an “X Proxy.” An X proxy acts as a virtual X server, receiving X11 commands from the application (and from VirtualGL), rendering the X11 commands into images, compressing the resulting images, and sending the compressed images over the network to a client or clients.

Since VirtualGL is sending rendered 3D images to the X proxy at a very fast rate, the proxy must be able to compress the images very quickly in order to keep up. But, unfortunately, most X proxies can’t. They simply aren’t designed for the types of full-screen video workloads that VirtualGL generates. Therefore, the VirtualGL Project provides an optimized X proxy called “TurboVNC”, which is based on the Virtual Network Computing (VNC) standard (more specifically, on the TightVNC variant thereof.)

On the surface, TurboVNC behaves very similarly to its parent project, but TurboVNC has been tuned to provide interactive performance for the types of full-screen video workloads that VirtualGL produces. On these types of image workloads, TurboVNC performs as much as an order of magnitude faster than TightVNC, uses more than an order of magnitude less CPU time to compress each frame, and it produces comparable compression ratios. Part of this speedup comes from the use of TurboJPEG, the same high-speed vector-optimized JPEG codec used by the VGL Image Transport. Another large part of the speedup comes from bypassing the color compression features of TightVNC. TightVNC performs very CPU-intensive analysis on each image tile to determine whether the tile will compress better using color compression or JPEG. But for the types of images that a 3D application generates, it is almost never the case that color compression compresses better than JPEG, so TurboVNC bypasses this analysis to improve performance. TurboVNC also has the ability to hide network latency by decompressing and drawing a frame on the client while the next frame is being fetched from the server, and this can improve performance dramatically on high-latency connections. TurboVNC additionally provides client-side double buffering, full support for Solaris, and other tweaks.

Advantages of TurboVNC (when compared to the VGL Image Transport)

• TurboVNC eliminates the need to send X11 traffic over the network, thus it performs very well on low-bandwidth, high-latency connections (such as broadband or long-haul T1 lines.) The 3D application’s GUI will load and render much faster (perhaps even orders of magnitude faster) with TurboVNC than with the VGL Image Transport on such connections.
• TurboVNC provides rudimentary collaboration capabilities. Multiple clients can simultaneously view the same server session and pass around control of the keyboard and mouse.
• The TurboVNC client is stateless. If the network hiccups or the client is otherwise disconnected, the session remains running on the server and can be rejoined from any machine on the network.
• No X server is required on the client machine. This reduces the deployment cost and complexity for Windows clients.

Disadvantages of TurboVNC

• No seamless windows. All application windows are constrained to a “virtual desktop”, which displays in a single window on the client machine.
• TurboVNC will generally require about 20% more server CPU cycles to maintain the same frame rate as the VGL Image Transport, both because it has to compress more pixels in each frame (an entire desktop rather than a single window) and because it has to perform 2D (X11) rendering as well as 3D rendering.
• TurboVNC does not support stereographic or overlay rendering.

9.1 Using TurboVNC and VirtualGL on the Same Server

The most common (and optimal) way to use TurboVNC is to set it up on the same server that is running VirtualGL. This allows VirtualGL to send its rendered 3D images to TurboVNC through shared memory rather than sending them over a network.

Procedure

1. Mac clients: Start the Mac X11 application.
2. Open a new Command Prompt/terminal window on your client machine. (Mac clients: in the X11 application, start a new xterm [Command-N] if one isn’t already started.)
3. In the new Command Prompt/terminal/xterm window, open a Secure Shell (SSh) session into the VirtualGL/TurboVNC server machine:

   Linux/Mac/Solaris clients

   ssh {user}@{server}
   

   Windows clients

   "c:\program files\turbovnc\putty" {user}@{server}
   

   Replace {user} with your user account name on the VirtualGL server and {server} with the hostname or IP address of that server.

4. In the SSh session, start a TurboVNC server session:

   /opt/TurboVNC/bin/vncserver
   

5. Make a note of the X display number that the TurboVNC server process prints out, for instance:
   
   New 'X' desktop is my_server:1
   
   If this is the first time that a TurboVNC server session has ever been run under this user account, TurboVNC will prompt for a VNC session password.
6. The SSh session can now be exited, if desired.
7. On the client machine, start the TurboVNC Viewer.

   Linux/Mac/Solaris clients

   Open a new terminal/xterm and type

   /opt/TurboVNC/bin/vncviewer
   

   Windows clients

   Select TurboVNC Viewer in the TurboVNC Start Menu group.

8. A small dialog box will appear.
   
   

   Windows TurboVNC viewer	Linux/Mac/Solaris TurboVNC viewer

   
   Enter the X display name (hostname/IP address and display number) of the TurboVNC server in the “VNC Server” field, then click “Connect” (Windows) or press Enter (Linux/Mac/Solaris.)
9. Another dialog box appears, prompting for the VNC session password.
   
   

   Windows TurboVNC viewer	Linux/Mac/Solaris TurboVNC viewer

   
   Enter the TurboVNC session password and click “OK” (Windows) or press Enter (Linux/Mac/Solaris.)
   
   A TurboVNC desktop window should appear on your client machine. This window contains a virtual X server with which you can interact to launch X-Windows applications on the TurboVNC server machine.
10. Open a new terminal inside the TurboVNC desktop.
11. In the terminal, start a 3D application using VirtualGL:

    /opt/VirtualGL/bin/vglrun [vglrun options] {application_executable_or_script} {arguments}
    

    VirtualGL will detect that the X display connection is local and will automatically enable the X11 Image Transport.
    Consult Chapter 19 for more information on vglrun command line options.

9.2 Using TurboVNC When VirtualGL Is Running on a Different Machine

If TurboVNC and VirtualGL are running on different servers, then it is desirable to use the VGL Image Transport to send images from the VirtualGL server to the TurboVNC server. It is also desirable to disable image compression in the VGL Image Transport. Otherwise, the images would have to be compressed by the VirtualGL server, decompressed by the VirtualGL Client, then recompressed by the TurboVNC server, which is a waste of CPU resources. However, sending images uncompressed over a network requires a fast network (generally, Gigabit Ethernet or faster.) So there needs to be a fast link between the VirtualGL server and the TurboVNC server for this procedure to perform well.

Procedure

The procedure for using the VGL Image Transport to transmit images from a VirtualGL server to a TurboVNC server is the same as the procedure for using the VGL Image Transport to transmit images to a remote X server, with the following notable differences:

1. The “client” in this case is really the TurboVNC server machine.
2. The “X server” is really the TurboVNC server session.
3. Once connected to the VirtualGL server with SSh, it is recommended that you disable image compression in the VGL Image Transport by either setting the environment variable VGL_COMPRESS to rgb or passing an argument of -c rgb to vglrun when launching VirtualGL. Otherwise, VirtualGL will detect that the connection to the X server is remote, and it will automatically try to enable JPEG compression.

9.3 Disconnecting and Killing the TurboVNC Session

Closing the TurboVNC viewer disconnects from the TurboVNC server session, but the TurboVNC server session is still running on the server machine (as are any applications that you may have started in it), and you can reconnect to the session at any time.

To kill a TurboVNC server session:

1. Using SSh (c:\Program Files\TurboVNC\putty.exe on Windows clients), log into the machine that is running the TurboVNC server session that you wish to kill.
   … or …
   Using the TurboVNC Viewer, connect to the TurboVNC server session that you wish to kill, and open a new terminal in that TurboVNC session.
2. Type the following command:

   /opt/TurboVNC/bin/vncserver -kill :{n}
   

   Replace {n} with the X display number of the TurboVNC server session you wish to kill.

To list the X display numbers and process ID’s of all TurboVNC server sessions that are currently running under your user account on this machine, run

/opt/TurboVNC/bin/vncserver -list

9.4 Using TurboVNC in a Web Browser

When a TurboVNC server session is created, it automatically launches a miniature web server that serves up a Java TurboVNC viewer applet. This Java TurboVNC viewer can be used to connect to the TurboVNC server from a machine that does not have a native TurboVNC viewer installed (or a machine for which no native TurboVNC viewer is available.) The Java viewer is significantly slower than the native viewer on high-speed networks, but on low-speed networks the Java viewer and native viewers have comparable performance. The Java viewer does not currently support double buffering.

To use the Java TurboVNC viewer, point your web browser to:

http://{turbovnc_server}:{5800+n}

where {turbovnc_server} is the hostname or IP address of the TurboVNC server machine, and n is the X display number of the TurboVNC server session to which you want to connect.

Example: If the TurboVNC server is running on X display my_server:1, then point your web browser to:

http://my_server:5801

9.5 Optimizing TurboVNC’s Performance for Different Network Types

The level of image compression in TurboVNC can be adjusted to balance the (sometimes conflicting) goals of high image quality and high performance. The more TurboVNC compresses an image, the more grainy the resulting image becomes. But these lower quality levels also require less network bandwidth and can thus improve the overall performance of TurboVNC on slower networks.

There are three options that control the level of image compression in TurboVNC:

Image compression type

Either “JPEG” or “None (RGB)”. “None (RGB)” turns off image compression altogether, which is useful when connecting to a TurboVNC server running on the same machine as the viewer or to a TurboVNC server located across a gigabit or faster network. Disabling image compression greatly reduces the CPU usage on the server and client, at the expense of greatly increasing the network usage.

JPEG image quality

Lower quality levels produce grainier JPEG images with more noticeable compression artifacts, but lower quality levels also use less network bandwidth and CPU power. Refer to Section 19.1 for more details.

JPEG chrominance subsampling

After converting the image from RGB to YUV, chrominance subsampling discards some of the U and V (chrominance) components to save space. 1x subsampling retains the chrominance components for all pixels, 2x subsampling retains the chrominance components for every other pixel, 4x subsampling retains the chrominance components for every fourth pixel, and grayscale throws out all of the chrominance components. Refer to Section 19.1 for more details.

In the Windows TurboVNC Viewer, these parameters can be adjusted by accessing the Options dialog box (click the “Options” button in the “TurboVNC Connection” dialog box or, after connecting to the server, click on the Connection Options button in the toolbar.) In the Unix TurboVNC viewer, press F8 after connecting to bring up the options menu. In the Java viewer, click on the Options button at the top of the browser window.

The TurboVNC Viewer provides three “connection profiles”, corresponding to three of the most useful levels of JPEG image compression:

In the Windows TurboVNC Viewer, there are three buttons in the “TurboVNC Connection” dialog box that allow you to easily select the connection profile. In the Java viewer, the same thing is accomplished by clicking the “Options” button at the top of the browser window. With the Linux/Mac/Solaris TurboVNC Viewer, the “High Quality” profile is the default, and you can use the -lowqual and -medqual command line options to vncviewer to switch to the “Low Quality” or “Medium Quality” profiles. You can also press the F8 key after connecting to pop up a menu from which you can select a different connection profile.

Lossless Refresh

TurboVNC can optionally encode images as RGB, which is fully lossless and uncompressed, but this mode does not perform well except on extremely fast networks. Another option for quality-critical applications is the “Lossless Refresh” feature. Lossless Refresh causes the server to send a mathematically lossless (Zlib-compressed RGB) copy of the current screen to the viewer. So, for instance, a user can rotate/pan/zoom an object in their application using a very lossy quality setting, then when that user is ready to interpret or analyze the object closely, they can request a lossless refresh of the screen.

To perform a lossless refresh, press CTRL-ALT-SHIFT-L in the Windows TurboVNC Viewer (or click on the Lossless Refresh toolbar icon.) In the Unix/Linux TurboVNC Viewer, select “Lossless Refresh” from the F8 popup menu. In the Java TurboVNC Viewer, click the “Lossless Refresh” button at the top of the browser window.

9.6 Securing a TurboVNC Connection

Normally, the connection between the TurboVNC server and the TurboVNC viewer is completely unencrypted, but securing that connection can be easily accomplished by using the port forwarding feature of Secure Shell (SSh.) After you have started a TurboVNC server session on the server machine, open a new SSh connection into the server machine using the following command line:

Linux/Mac/Solaris clients

ssh -L {5900+n}:localhost:{5900+n} {user}@{server}

Windows clients

"c:\program files\turbovnc\putty" -L {5900+n}:localhost:{5900+n} {user}@{server}

Replace {user} with your user account name on the TurboVNC server and {server} with the hostname or IP address of that server. Replace n with the X display number of the TurboVNC server session to which you want to connect.

For instance, if you wish to connect to display :1 on server my_server using user account my_user, you would type:

Linux/Mac/Solaris clients

ssh -L 5901:localhost:5901 my_user@my_server

Windows clients

"c:\program files\turbovnc\putty" -L 5901:localhost:5901 my_user@my_server

After the SSh connection has been established, you can then launch the TurboVNC viewer and point it to localhost:{n} (localhost:1 in the above example.)

Performance Notes

For LAN connections and other high-speed networks, tunneling the TurboVNC connection over SSh will reduce performance by as much as 20-40%. But for wide-area networks, broadband, etc., there is no performance penalty for using SSh tunneling with TurboVNC.

9.7 Further Reading

For more detailed instructions on the usage of TurboVNC:

Linux and Solaris

Refer to the TurboVNC man pages:

man -M /opt/TurboVNC/man {vncserver | Xvnc | vncviewer | vncconnect | vncpasswd}

Windows

Use the embedded help feature (the question mark button in the upper right of the TurboVNC Viewer window.)

The TightVNC documentation:

http://www.tightvnc.com/docs.html

might also be helpful, since TurboVNC is based on TightVNC and shares many of its features.

10 Using VirtualGL with Other X Proxies

The previous chapter described how to use VirtualGL with TurboVNC, but much of this information is also applicable to other X proxies, such as RealVNC, NX, etc. Generally, none of these other solutions will provide anywhere near the performance of TurboVNC, but some of them have capabilities that TurboVNC lacks (NX, for instance, can do seamless windows.)

VirtualGL reads the value of the DISPLAY environment variable to determine whether to enable the X11 Image Transport by default. If DISPLAY begins with a colon (“:”) or with “unix:”, then VirtualGL will assume that the X server connection is local and will enable the X11 Image Transport as the default. This should effectively make the X11 Image Transport the default for most X proxies, but if for some reason that doesn’t occur, then you can force the use of the X11 Image Transport by setting VGL_COMPRESS to proxy or passing an argument of -c proxy to vglrun.

11 Using VirtualGL in a Sun Ray Environment

As described in Chapter 2, the Sun Ray environment consists of both an X proxy and an ultra-thin hardware client. If the proprietary VirtualGL Sun Ray plugin is not used, then the Sun Ray server can be treated just like any other X proxy and used with either the X11 Image Transport or the VGL Image Transport, as described in Chapter 9 and Chapter 10.

If, however, the Sun Ray plugin is installed on the VirtualGL server, then a slightly different procedure is required to connect to that server and use the Sun Ray Image Transport. This procedure assumes that VirtualGL is running on a different machine than the Sun Ray server.

Procedure

1. In the Sun Ray session, open a new terminal window.
2. In the same terminal window, open a Secure Shell (SSh) session into the VirtualGL server:

   ssh -X {user}@{server}
   

   Replace {user} with your user account name on the VirtualGL server and {server} with the hostname or IP address of that server.
3. In the SSh session, start a 3D application using VirtualGL:

   /opt/VirtualGL/bin/vglrun [vglrun options] {application_executable_or_script} {arguments}
   

   Consult Chapter 19 for more information on vglrun command line options.

Note that this procedure is substantially similar to the X11 Forwarding procedure used with the VGL Image Transport, except that it invokes ssh directly rather than using the vglconnect wrapper script. vglconnect launches vglclient, and vglclient is not needed when using the Sun Ray Image Transport.

If the VirtualGL Sun Ray plugin is installed on a VirtualGL server machine, then VirtualGL will try to use the Sun Ray Image Transport when displaying 3D applications from that server to a Sun Ray. However, the Sun Ray Image Transport requires that the Sun Ray client be on a network that is accessible from the VirtualGL server. Some Sun Ray deployments place the clients on a private network that is visible only to the Sun Ray server, and the Sun Ray Image Transport cannot be used in such cases (unless VirtualGL is running on the Sun Ray server itself, but that defeats the purpose of the Sun Ray Image Transport.) If VirtualGL detects that it is running in a Sun Ray environment but is unable to use the Sun Ray Image Transport, then it will fall back to using the X11 Image Transport.

12 vglrun and Shell Scripts

vglrun can be used to launch either binary executables or shell scripts, but there are a few things to keep in mind when using vglrun to launch a shell script. When you vglrun a shell script, the VirtualGL faker library will be preloaded into every executable that the script launches. Normally this is innocuous, but if the script calls any executables that are setuid and/or setgid, then the dynamic linker will refuse to preload the VirtualGL faker library into those executables. The following warning will be printed out for each setuid/setgid executable that the script tries to launch:

Linux

ERROR: ld.so: object 'librrfaker.so' from LD_PRELOAD cannot be preloaded: ignored.

Solaris

ld.so.1: warning: librrfaker.so: open failed: No such file in secure directories

On Solaris and on newer versions of Linux (Enterprise Linux 3 and later), the executable will continue to run, but without VirtualGL preloaded into it. That may be a problem, if the setuid/setgid executable was a 3D application that was intended to be used with VirtualGL. To further complicate matters, some older versions of Linux will refuse to launch setuid/setgid executables at all if one attempts to preload VirtualGL into them.

There are a couple of ways to work around this issue. Probably the safest way is to simply edit the application script and make it store the value of the LD_PRELOAD environment variables until right before the application executable is launched. For instance, take the following application script (please):

Initial contents of application.sh:

#!/bin/sh
some_setuid_executable
some_application_executable

You could modify the script as follows:

Solaris

Modified application.sh:

#!/bin/sh
LD_PRELOAD_32_SAVE=$LD_PRELOAD_32
LD_PRELOAD_64_SAVE=$LD_PRELOAD_64
LD_PRELOAD_32=
LD_PRELOAD_64=
export LD_PRELOAD_32 LD_PRELOAD_64

some_setuid_executable

LD_PRELOAD_32=$LD_PRELOAD_32_SAVE
LD_PRELOAD_64=$LD_PRELOAD_64_SAVE
export LD_PRELOAD_32 LD_PRELOAD_64

some_application_executable

Linux

Modified application.sh:

#!/bin/sh
LD_PRELOAD_SAVE=$LD_PRELOAD
LD_PRELOAD=
export LD_PRELOAD

some_setuid_executable

LD_PRELOAD=$LD_PRELOAD_SAVE
export LD_PRELOAD

some_application_executable

You can also force VirtualGL to be preloaded into setuid/setgid executables, but please be aware of the security ramifications of this before you do it. By applying one of the following workarounds, you are essentially telling the operating system that you trust the security and stability of the VirtualGL code as much as you trust the security and stability of the operating system. And while we’re flattered, we’re not sure that we’re necessarily deserving of that accolade, so if you are in a security critical environment, apply the appropriate level of paranoia here.

To force VirtualGL to be preloaded into setuid/setgid executables on Linux, make librrfaker.so a setuid executable. To do this, run the following command as root:

chmod u+s /usr/lib/librrfaker.so

On 64-bit Linux systems, also run:

chmod u+s /usr/lib64/librrfaker.so

On Solaris, you can force VirtualGL to be preloaded into setuid/setgid executables by adding the VirtualGL library directories to the Solaris “secure path.” Solaris keeps a tight lid on what goes into /usr/lib and /lib, and by default, it will only allow libraries in those paths to be preloaded into an executable that is setuid and/or setgid. Generally, 3rd party packages are verboden from installing anything into /usr/lib or /lib. But you can use the crle utility to add other directories to the operating system’s list of secure paths. In the case of VirtualGL, you would execute the following commands (as root):

crle -u -s /opt/SUNWvgl/lib
crle -64 -u -s /opt/SUNWvgl/lib/64

vglrun on Solaris has two additional options that are relevant to launching scripts:

vglrun -32 {script}

will preload VirtualGL only into 32-bit executables called by a script, whereas

vglrun -64 {script}

will preload VirtualGL only into 64-bit executables. So if, for instance, the setuid executable that the script is invoking is 32-bit and the application executable is 64-bit, then you could use vglrun -64 to launch the application script.

13 Using VirtualGL with Applications That Manually Load OpenGL

The lion’s share of OpenGL applications are dynamically linked against libGL.so, and thus libGL.so is automatically loaded whenever the application loads. Whenever vglrun is used to launch such applications, VirtualGL is loaded ahead of libGL.so, meaning that OpenGL and GLX symbols are resolved from VirtualGL first and the “real” OpenGL library second.

However, some applications (particularly games) are not dynamically linked against libGL.so. These applications typically call dlopen() and dlsym() later on in the program’s execution to manually load OpenGL and GLX symbols from libGL.so. Such applications also generally provide a mechanism (usually either an environment variable or a command line argument) which allows the user to specify a library that can be loaded instead of libGL.so.

So let’s assume that you just downloaded the latest version of the Linux game Foo Wars from the Internet, and (for whatever reason) you want to run the game in a VNC session. The game provides a command line switch -g which can be used to specify an OpenGL library to load other than libGL.so. You would launch the game using a command line such as this:

vglrun foowars -g /usr/lib/librrfaker.so

You still need to use vglrun to launch the game, because VirtualGL must also intercept a handful of X11 calls. Using vglrun allows VGL to intercept these calls, whereas using the game’s built-in mechanism for loading a substitute OpenGL library allows VirtualGL to intercept the GLX and OpenGL calls.

In some cases, the application doesn’t provide an override mechanism such as the above. In these cases, you should pass an argument of -dl to vglrun when starting the application. For example:

vglrun -dl foowars

Passing -dl to vglrun forces another library to be loaded ahead of VirtualGL and libGL.so. This new library intercepts any calls to dlopen() and forces the application to open VirtualGL instead of libGL.so.

Chapter 15 contains specific recipes for getting a variety of games and other applications to work with VirtualGL.

14 Using VirtualGL with Chromium and ModViz VGP

Chromium is a powerful framework for performing various types of parallel OpenGL rendering. It is usually used on clusters of commodity Linux PC’s to divide up the task of rendering scenes with large geometries or large pixel counts (such as when driving a display wall.) Chromium is most often used in one of three configurations:

1. Sort-First Rendering (Image-Space Decomposition)
2. Sort-First Rendering (Image-Space Decomposition) with Readback
3. Sort-Last Rendering (Object-Space Decomposition)

14.1 Configuration 1: Sort-First Rendering (Image-Space Decomposition)

Sort-First Rendering (Image-Space Decomposition) is used to overcome the fill rate limitations of individual graphics cards. When configured to use sort-first rendering, Chromium divides up the scene based on which polygons will be visible in a particular section of the final image. It then instructs each node of the cluster to render only the polygons that are necessary to generate the image section (“tile”) for that node. This is primarily used to drive high-resolution displays that would be impractical to drive from a single graphics card due to limitations in the card’s framebuffer memory, processing power, or both. Configuration 1 could be used, for instance, to drive a CAVE, video wall, or even an extremely high-resolution monitor. In this configuration, each Chromium node generally uses all of its screen real estate to render a section of the multi-screen image.

VirtualGL is generally not very useful with Configuration 1. You could theoretically install a separate copy of VirtualGL on each display node and use it to redirect the output of each crserver instance to a multi-screen X server running elsewhere on the network. But there would be no way to synchronize the screens on the remote end. Chromium uses DMX to synchronize the screens in a multi-screen configuration, and VirtualGL would have to be made DMX-aware for it to perform the same job. Maybe at some point in the future … If you have a need for such a configuration, let us know.

14.2 Configuration 2: Sort-First Rendering (Image-Space Decomposition) with Readback

Configuration 2 uses the same sort-first principle as Configuration 1, except that each tile is only a fraction of a single screen, and the tiles are recombined into a single window on Node 0. This configuration is perhaps the least often used of the three, but it is useful in cases where the scene contains a large amount of textures (such as in volume rendering) and thus rendering the whole scene on a single node would be prohibitively slow due to fill rate limitations.

In this configuration, the application is allowed to choose a visual, create an X window, and manage the window as it would normally do. But all other OpenGL and GLX activity is intercepted by the Chromium App Faker (CrAppFaker) so that the rendering task can be split up among the rendering nodes. Once each node has rendered its section of the final image, the tiles get passed back to a Chromium Server (CrServer) process running on Node 0. This CrServer process attaches to the previously-created application window and draws the pixels into it using glDrawPixels().

The general strategy for making this work with VirtualGL is to first make it work without VirtualGL and then insert VirtualGL only into the processes that run on Node 0. VirtualGL must be inserted into the CrAppFaker process to prevent CrAppFaker from sending glXChooseVisual() calls to the X server (which would fail if the X server is a VNC server or otherwise does not provide GLX.) VirtualGL must be inserted into the CrServer process on Node 0 to prevent it from sending glDrawPixels() calls to the X server (which would effectively send uncompressed images over the network.) Instead, VirtualGL forces CrServer to draw into a Pbuffer, and VGL takes charge of transmitting those pixels to the destination X server in the most efficient way possible.

Since Chromium uses dlopen() to load the system’s OpenGL library, preloading VirtualGL into the CrAppFaker and CrServer processes using vglrun is not sufficient. Fortunately, Chromium provides an environment variable, CR_SYSTEM_GL_PATH, which allows one to specify an alternate path in which it will search for the system’s libGL.so. The VirtualGL packages for Linux and Solaris include a symbolic link named libGL.so which really points to the VirtualGL faker library (librrfaker.so) instead. This symbolic link is located in its own isolated directory, so that directory can be passed to Chromium in the CR_SYSTEM_GL_PATH environment variable, thus causing Chromium to load VirtualGL rather than the “real” OpenGL library. Refer to the following table:

Running the CrServer in VirtualGL is simply a matter of setting this environment variable and then invoking crserver with vglrun. For example:

export CR_SYSTEM_GL_PATH=/opt/VirtualGL/fakelib
vglrun crserver

In the case of CrAppFaker, it is also necessary to set VGL_GLLIB to the location of the “real” OpenGL library (example: /usr/lib/libGL.so.1.) CrAppFaker creates its own fake version of libGL.so which is really just a copy of Chromium’s libcrfaker.so. So VirtualGL, if left to its own devices, will unwittingly try to load libcrfaker.so instead of the “real” OpenGL library. Chromium’s libcrfaker.so will in turn try to load VirtualGL again, and an endless loop will occur.

So what we want to do is something like this:

export CR_SYSTEM_GL_PATH=/opt/VirtualGL/fakelib
export VGL_GLLIB=/usr/lib/libGL.so.1
crappfaker

CrAppFaker will copy the application to a temp directory and then copy libcrfaker.so to that same directory, renaming it as libGL.so. So when the application is started, it loads libcrfaker.so instead of libGL.so. libcrfaker.so will then load VirtualGL instead of the “real” libGL, because we’ve overridden CR_SYSTEM_GL_PATH to make Chromium find VirtualGL’s fake libGL.so first. VirtualGL will then use the library specified in VGL_GLLIB to make any “real” OpenGL calls that it needs to make.

Note that crappfaker should not be invoked with vglrun.

So, putting this all together, here is an example of how you might start a sort-first rendering job using Chromium and VirtualGL:

1. Start the mothership on Node 0 with an appropriate configuration for performing sort-first rendering with readback
2. Start crserver on each of the rendering nodes
3. On Node 0, set CR_SYSTEM_GL_PATH to the appropriate value for the operating system and application type (see table above)
4. On Node 0, vglrun crserver &
5. On Node 0, set VGL_GLLIB to the location of the “real” libGL (example: /usr/lib/libGL.so.1 or /usr/lib64/libGL.so.1.)
6. On Node 0, launch crappfaker (do not use vglrun here)

Again, it’s always a good idea to make sure this works without VirtualGL before adding VirtualGL into the mix.

Using VirtualGL to Force Pbuffer Rendering

In the procedure above, VirtualGL can also be used on the rendering nodes to redirect the rendering commands from crserver into a Pbuffer instead of a window. If you wish to do this, then perform the following procedure in place of step 2 above:

On each of the rendering nodes,

• set VGL_READBACK=0
• set CR_SYSTEM_GL_PATH to the appropriate value based on the rendering node’s operating system type and whether crserver was compiled as a 32-bit or 64-bit app on that node (see table above)
• vglrun crserver

14.3 Configuration 3: Sort-Last Rendering (Object-Space Decomposition)

Sort-Last Rendering is used when the scene contains a huge number of polygons and the rendering bottleneck is processing all of that geometry on a single graphics card. In this case, each node runs a separate copy of the application, and for best results, the application needs to be at least partly aware that it’s running in a parallel environment so that it can give Chromium hints as to how to distribute the various objects to be rendered. Each node generates an image of a particular portion of the object space, and these images must be composited in such a way that the front-to-back ordering of pixels is maintained. This is generally done by collecting Z buffer data from each node to determine whether a particular pixel on a particular node is visible in the final image. The rendered images from each node are often composited using a “binary swap”, whereby the nodes combine their images in a cascading tree so that the overall compositing time is proportional to log₂(N) rather than N.

To make this configuration work with VirtualGL:

1. Start the mothership on Node 0 with an appropriate configuration for performing sort-last rendering
2. Start crappfaker on each of the rendering nodes
3. On Node 0, set CR_SYSTEM_GL_PATH to the appropriate value for the operating system and application type (see table in Section 14.2.)
4. On Node 0, vglrun crserver

CRUT

The Chromium Utility Toolkit provides a convenient way for graphics applications to specifically take advantage of Chromium’s sort-last rendering capabilities. Such applications can use CRUT to explicitly specify how their object space should be decomposed. CRUT applications require an additional piece of software, crutserver, to be running on Node 0. So to make such applications work with VirtualGL:

1. Start the mothership on Node 0 with an appropriate configuration for performing sort-last rendering
2. Start crappfaker on each of the rendering nodes
3. On Node 0, set CR_SYSTEM_GL_PATH to the appropriate value for the operating system and application type (see table in Section 14.2.)
4. On Node 0, vglrun crutserver &
5. On Node 0, vglrun crserver

14.4 A Note About Performance

Chromium’s use of X11 is generally not very optimal. It assumes a very fast connection between the X server and the Chromium Server. In certain modes, Chromium polls the X server on every frame to determine whether windows have been resized, etc. Thus, we have observed that, even on a fast network, Chromium tends to perform much better with VirtualGL running in a TurboVNC session as opposed to using the VGL Image Transport.

14.5 ModViz VGP and VirtualGL

ModViz Virtual Graphics Platform^TM is a polished commercial clustered rendering framework for Linux which supports all three of the rendering modes described above and provides a much more straightforward interface to configure and run these types of parallel rendering jobs.

All VGP jobs, regardless of configuration, are all spawned through vglauncher, a front-end program which automatically takes care of starting the appropriate processes on the rendering nodes, intercepting OpenGL calls from the application instance(s), sending rendered images back to Node 0, and compositing the images as appropriate. In a similar manner to VirtualGL’s vglrun, VGP’s vglauncher preloads a library (libVGP.so) in place of libGL.so, and this library intercepts the OpenGL calls from the application.

So our strategy here is similar to our strategy for loading the Chromium App Faker. We want to insert VirtualGL between VGP and the real system OpenGL library, so that VGP will call VirtualGL and VirtualGL will call libGL.so. Achieving this with VGP is relatively simple:

export VGP_BACKING_GL_LIB=librrfaker.so
vglrun vglauncher --preload=librrfaker.so:/usr/lib/libGL.so {application}

Replace /usr/lib/libGL.so with the full path of your system’s OpenGL library (/usr/lib64/libGL.so if you are launching a 64-bit application.)

15 Other Application Recipes

Notes for ANSYS and Pro/E

ANSYS and Pro/E frequently render to the front buffer and, for unknown reasons, call glFlush() thousands of times in a row even if nothing new has been rendered. This exposes a vulnerability in VirtualGL’s framebuffer readback heuristics. Normally, when an application calls glFlush() on the front buffer, VirtualGL will read back, compress, and send the pixels from the front buffer. But if glFlush() is called thousands of times without changing the contents of the frame buffer, this causes VirtualGL to read back, compress, and send thousands of duplicate images. Whereas calling glFlush() on a local display takes practically no time, reading back and sending an image in VirtualGL takes a relatively long amount of time. So, left unchecked, this phenomenon can lead to delays of several minutes when performing certain operations in ANSYS and Pro/E while using VirtualGL.

If frame spoiling is enabled, then VirtualGL will not read back the framebuffer in response to a glFlush() call if a prior image is still being compressed/sent. Ideally, this would cause most of the duplicate glFlush() calls to be ignored by VirtualGL. However, this frame spoiling algorithm only works if it takes longer to compress and send an image than it does to read it back from the framebuffer. Frames are spoiled during the time that the readback thread is waiting for the compressor thread to finish with the previous frame, so if the readback thread never has to wait on the compressor thread, then no frames are ever spoiled. There are several reasons why this could occur:

1. The system contains an old, slow bus (AGP, for instance) and thus the readback performance from the graphics card is relatively slow.
2. TurboVNC is being used on the same server as VirtualGL. If this is the case, then the compressor thread is passing images to TurboVNC through shared memory, which (even on modern systems) is almost always faster than reading back images from the graphics card.
3. Interframe comparison is enabled in the VGL Image Transport. In the case of ANSYS and Pro/E, each duplicate frame can be compared and discarded by the compressor much more quickly than it can be read back from the graphics card, so no spoiling occurs.

A more robust fix for this problem is slated for the next release of VirtualGL, but for now, it is necessary to work around the issue if it occurs. The workaround is essentially to slow the compressor thread down such that it is slower than the readback thread. When using the VGL Image Transport, it is usually only necessary to disable interframe comparison (VGL_INTERFRAME=0) to accomplish this. But when using the X11 Image Transport and TurboVNC, it is necessary to introduce an artificial delay into the compressor thread by setting VGL_FPS. A value of 20 for VGL_FPS is a reasonable starting point, but you may have to decrease this value if the readback performance on your system is exceptionally slow.

16 Advanced OpenGL Features

16.1 Stereographic Rendering

Stereographic rendering is a feature of OpenGL that creates separate rendering buffers for the left and right eyes and allows the application to render a different image into each buffer. How the stereo images are subsequently displayed depends on the particulars of the 3D hardware and the user’s environment. VirtualGL can support stereographic applications in one of two ways: (1) by sending the stereo image pairs to the client to be displayed in stereo by the client’s 3D graphics card, or (2) by combining each stereo image pair into a single anaglyph that can be viewed with traditional red/cyan 3D glasses.

16.1.1 Quad-Buffered Stereo

The name “quad-buffered” stereo derives from the fact that OpenGL uses four buffers (left front, right front, left back, and right back) to support stereographic rendering with double buffering. 3D graphics cards with quad-buffered stereo capabilities generally provide some sort of synchronization signal that can be used to control various types of active stereo 3D glasses. Some also support “passive stereo”, which displays the left and right eye buffers to different monitor outputs. VirtualGL supports true quad-buffered stereo by rendering the stereo images on the server and sending the image pairs across the network to be displayed by a 3D graphics card on the client.

In most cases, the VirtualGL and TurboVNC clients use only 2D drawing commands, thus eliminating the need for a 3D graphics card on the client machine. But drawing stereo images requires a 3D graphics card, so such a card must be present in any client machine that will use VirtualGL’s quad-buffered stereo mode. Since the 3D graphics card is only being used to draw images, it need not necessarily be a high-end card. Generally, the least expensive 3D graphics card that has stereo capabilities will work fine in a VirtualGL client.

The server must also have a 3D graphics card that supports stereo, since this is the only way that VirtualGL can obtain a stereo Pbuffer. When an application tries to render something in stereo, VirtualGL will (by default) use quad-buffered stereo rendering if:

• The client supports OpenGL (Exceed 3D is required for Windows clients)
• The client has stereo rendering capabilities
• The server has stereo rendering capabilities

If one or more of these is not true, then VirtualGL will fall back to using anaglyphic stereo (see below.) It is usually necessary to explicitly enable stereo in the graphics driver configuration for both the client and server machines. The Troubleshooting section below lists a way to verify that both client and server have stereo visuals available.

In quad-buffered mode, VirtualGL reads back both eye buffers on the server and sends the contents as a pair of compressed images (one for each eye) to the VirtualGL Client. The VirtualGL Client then decompresses both images and draws them as a single stereo frame to the client machine’s X display using glDrawPixels(). It should thus be no surprise that enabling quad-buffered stereo in VirtualGL decreases performance by 50% or more and uses twice the network bandwidth to maintain the same frame rate.

Quad-buffered stereo requires the VGL Image Transport. If any other image transport is used, then VGL will fall back to anaglyphic stereo mode.

16.1.2 Anaglyphic Stereo

Anaglyphic stereo is the type of stereographic display used by old 3D movies. It generally relies on a set of 3D glasses consisting of red transparency film over the left eye and cyan transparency film over the right eye. To generate a 3D anaglyph, the red color data from the left eye buffer is combined with the green and blue color data from the right eye buffer, thus allowing a single monographic image to contain stereo data. From the point of view of VirtualGL, an anaglyphic image is the same as a monographic image, so anaglyphic stereo images can be sent using any image transport to any type of client, regardless of the client’s capabilities.

VirtualGL uses anaglyphic stereo if it detects that an application has rendered something in stereo but quad-buffered stereo is not available, either because the client doesn’t support it or because a transport other than the VGL Image Transport is being used. Anaglyphic stereo provides a cheap and easy way to view stereographic applications in X proxies and on clients that do not support quad-buffered stereo. Additionally, anaglyphic stereo performs much faster than quad-buffered stereo, since it does not require sending twice the data to the client.

As with quad-buffered stereo, anaglyphic stereo requires that the server have stereo rendering capabilities. However, anaglyphic stereo does not require any 3D rendering capabilities (stereo or otherwise) on the client.

16.1.3 Selecting a Stereo Mode

A particular stereo mode can be selected by setting the VGL_STEREO environment variable or by using the -st argument to vglrun. See Section 19.1 for more details.

16.2 Transparent Overlays

Transparent overlays have similar requirements and restrictions as quad-buffered stereo. In this case, VirtualGL completely bypasses its own GLX faker and uses indirect OpenGL rendering to render the transparent overlay on the client machine’s 3D graphics card. The underlay is still rendered on the server, as always. Using indirect rendering to render the overlay is unfortunately necessary, because there is no reliable way to draw to an overlay using 2D (X11) functions, there are severe performance issues (on some cards) with using glDrawPixels() to draw to the overlay, and there is no reasonable way to composite the overlay and underlay on the VirtualGL server.

The use of overlays is becoming more and more infrequent, and when they are used, it is generally only for drawing small, simple, static shapes and text. We have found that it is often faster to send the overlay geometry over to the client rather than to render it as an image and send the image. So even if it were possible to implement overlays without using indirect rendering, it’s likely that indirect rendering of overlays would still be the fastest approach for most applications.

As with stereo, overlays must sometimes be explicitly enabled in the graphics card’s configuration. In the case of overlays, however, they need only be supported and enabled on the client machine.

Indexed color (8-bit) overlays have been tested and are known to work with VirtualGL. True color (24-bit) overlays work, in theory, but have not been tested. Use glxinfo (see Troubleshooting below) to verify whether your client’s X display supports overlays and whether they are enabled. In Exceed 3D, make sure that the “Overlay Support” option is checked in the “Exceed 3D and GLX” applet:

16.3 Indexed (PseudoColor) Rendering

In a PseudoColor visual, each pixel is represented by an index which refers to a location in a color table. The color table stores the actual color values (256 of them in the case of 8-bit PseudoColor) which correspond to each index. An application merely tells the X server which color index to use when drawing, and the X server takes care of mapping that index to an actual color from the color table. OpenGL allows for rendering to Pseudocolor visuals, and it does so by being intentionally ignorant of the relationship between indices and actual colors. As far as OpenGL is concerned, each color index value is just a meaningless number, and it is only when the final image is drawn by the X server that these numbers take on meaning. As a result, many pieces of OpenGL’s core functionality either have undefined behavior or do not work at all with PseudoColor rendering. PseudoColor rendering used to be a common technique to visualize scientific data, because such data often only contained 8 bits per sample to begin with. Applications could manipulate the color table to allow the user to dynamically control the relationship between sample values and colors. As more and more graphics cards drop support for PseudoColor rendering, however, the applications which use it are becoming a vanishing breed.

VirtualGL supports PseudoColor rendering if a PseudoColor visual is available on the client’s display. A PseudoColor visual need not be present on the server. On the server, VirtualGL uses the red channel of a standard RGB Pbuffer to store the color index. Upon receiving an end of frame trigger, VirtualGL reads back the red channel of the Pbuffer and uses XPutImage() to draw the color indices into the appropriate X window. To put this another way, PseudoColor rendering in VirtualGL always uses the X11 Image Transport. However, since there is only 1 byte per pixel in a PseudoColor “image”, the images can still be sent to the client reasonably quickly even though they are uncompressed.

VirtualGL’s PseudoColor rendering support works with VNC, provided that the VNC server is configured with an 8-bit color depth. TurboVNC does not support 8-bit color depths, but RealVNC and other VNC flavors do. Note, however, that VNC cannot provide both PseudoColor and TrueColor visuals at the same time.

16.4 Troubleshooting

VirtualGL includes a modified version of glxinfo that can be used to determine whether or not the client and server have stereo, overlay, or Pseudocolor visuals enabled.

Run one of the following command sequences on the VirtualGL server to determine whether the server has a suitable visual for stereographic rendering:

Solaris servers (using GLP)

/opt/VirtualGL/bin/glxinfo -d {glp_device} -v

Linux and Solaris servers (not using GLP)

xauth merge /etc/opt/VirtualGL/vgl_xauth_key
/opt/VirtualGL/bin/glxinfo -display :0 -c -v

One or more of the visuals should say “stereo=1” and should list “Pbuffer” as one of the “Drawable Types.”

Run the following command sequence on the VirtualGL server to determine whether the X display on the client has a suitable visual for stereographic rendering, transparent overlays, or Pseudocolor.

/opt/VirtualGL/bin/glxinfo -v

In order to use stereo, one or more of the visuals should say “stereo=1”. In order to use transparent overlays, one or more of the visuals should say “level=1”, should list a “Transparent Index” (non-transparent visuals will say “Opaque” instead), and should have a class of “PseudoColor.” In order to use PseudoColor (indexed) rendering, one of the visuals should have a class of “PseudoColor.”

17 Performance Measurement

17.1 VirtualGL’s Built-In Profiling System

The easiest way to uncover bottlenecks in VirtualGL’s image pipelines is to set the VGL_PROFILE environment variable to 1 on both server and client (passing an argument of +pr to vglrun on the server has the same effect.) This will cause VirtualGL to measure and report the throughput of the various stages in the pipeline. For example, here are some measurements from a dual Pentium 4 server communicating with a Pentium III client on a 100 Megabit LAN:

Server

Readback   - 43.27 Mpixels/sec - 34.60 fps
Compress 0 - 33.56 Mpixels/sec - 26.84 fps
Total      -  8.02 Mpixels/sec -  6.41 fps - 10.19 Mbits/sec (18.9:1)

Client

Decompress - 10.35 Mpixels/sec -  8.28 fps
Blit       - 35.75 Mpixels/sec - 28.59 fps
Total      -  8.00 Mpixels/sec -  6.40 fps - 10.18 Mbits/sec (18.9:1)

The total throughput of the pipeline is 8.0 Megapixels/sec, or 6.4 frames/sec, indicating that our frame is 8.0 / 6.4 = 1.25 Megapixels in size (a little less than 1280 x 1024 pixels.) The readback and compress stages, which occur in parallel on the server, are obviously not slowing things down. And we’re only using 1/10 of our available network bandwidth. So we look to the client and discover that its slow decompression speed (10.35 Megapixels/second) is the primary bottleneck. Decompression and blitting on the client cannot be done in parallel, so the aggregate performance is the harmonic mean of the decompression and blitting rates: [1/ (1/10.35 + 1/35.75)] = 8.0 Mpixels/sec.

17.2 Frame Spoiling

By default, VirtualGL will only send a frame to the client if the client is ready to receive it. If a rendered frame arrives at the server’s queue and there are frames waiting in the queue to be processed, then those unprocessed frames are dropped (“spoiled”) and the new frame is promoted to the head of the queue. This prevents a backlog of frames on the server, which would cause a perceptible delay in the responsiveness of interactive applications. However, when running non-interactive applications, particularly benchmarks, frame spoiling should always be disabled. With frame spoiling disabled, the server will render frames only as quickly as VirtualGL can send those frames to the client, which will conserve server resources as well as allow OpenGL benchmarks to accurately measure the frame rate of the VirtualGL system. With frame spoiling enabled, OpenGL benchmarks will report meaningless data, since the rate at which the server can render frames is decoupled from the rate at which VirtualGL can send those frames to the client.

In a VNC environment, there is another layer of frame spoiling, since the server only sends updates to the client when the client requests them. So even if frame spoiling is disabled in VirtualGL, OpenGL benchmarks will still report meaningless data if they are run in a VNC session. TCBench, described below, provides a limited solution to this problem.

To disable frame spoiling, set the VGL_SPOIL environment variable to 0 on the server or pass an argument of -sp to vglrun. See Section 19.1 for more details.

17.3 VirtualGL Diagnostic Tools

VirtualGL includes several tools which can be useful in diagnosing performance problems with the system.

NetTest

NetTest is a network benchmark that uses the same network I/O classes as VirtualGL. It can be used to test the latency and throughput of any TCP/IP connection, with or without SSL encryption. nettest can be found in /opt/VirtualGL/bin on Linux/Mac/Solaris VirtualGL installations or in c:\program files\VirtualGL-{version}-{build} on Windows installations.

To use NetTest, first start up the nettest server on one end of the connection:

nettest -server [-ssl]

(use -ssl if you want to test the performance of SSL encryption over this particular connection.)

Next, start the client on the other end of the connection:

nettest -client {server} [-ssl]

Replace {server} with the hostname or IP address of the machine where the NetTest server is running. Use -ssl if the NetTest server is running in SSL mode.)

The nettest client will produce output similar to the following:

TCP transfer performance between localhost and {server}:

Transfer size  1/2 Round-Trip      Throughput      Throughput
(bytes)                (msec)        (MB/sec)     (Mbits/sec)
1                    0.093402        0.010210        0.085651
2                    0.087308        0.021846        0.183259
4                    0.087504        0.043594        0.365697
8                    0.088105        0.086595        0.726409
16                   0.090090        0.169373        1.420804
32                   0.093893        0.325026        2.726514
64                   0.102289        0.596693        5.005424
128                  0.118493        1.030190        8.641863
256                  0.146603        1.665318       13.969704
512                  0.205092        2.380790       19.971514
1024                 0.325896        2.996542       25.136815
2048                 0.476611        4.097946       34.376065
4096                 0.639502        6.108265       51.239840
8192                 1.033596        7.558565       63.405839
16384                1.706110        9.158259       76.825049
32768                3.089896       10.113608       84.839091
65536                5.909509       10.576174       88.719379
131072              11.453894       10.913319       91.547558
262144              22.616389       11.053931       92.727094
524288              44.882406       11.140223       93.450962
1048576             89.440702       11.180592       93.789603
2097152            178.536997       11.202160       93.970529
4194304            356.754396       11.212195       94.054712

We can see that the throughput peaks at about 94 megabits/sec, which is pretty good for a 100 Megabit connection. We can also see that, for small transfer sizes, the round-trip time is dominated by latency. The “latency” is the same thing as the 1/2 round-trip time for a zero-byte packet, which is about 93 microseconds in this case.

CPUstat

CPUstat is available only in the VirtualGL Linux packages and is located in the same place as NetTest (/opt/VirtualGL/bin.) It measures the average, minimum, and peak CPU usage for all processors combined and for each processor individually. On Windows, this same functionality is provided in the Windows Performance Monitor, which is part of the operating system. On Solaris, the same data can be obtained through vmstat.

CPUstat measures the CPU usage over a given sample period (a few seconds) and continuously reports how much the CPU was utilized since the last sample period. Output for a particular sample looks something like this:

ALL :  51.0 (Usr= 47.5 Nice=  0.0 Sys=  3.5) / Min= 47.4 Max= 52.8 Avg= 50.8
cpu0:  20.5 (Usr= 19.5 Nice=  0.0 Sys=  1.0) / Min= 19.4 Max= 88.6 Avg= 45.7
cpu1:  81.5 (Usr= 75.5 Nice=  0.0 Sys=  6.0) / Min= 16.6 Max= 83.5 Avg= 56.3

The first column indicates what percentage of time the CPU was active since the last sample period (this is then broken down into what percentage of time the CPU spent running user, nice, and system/kernel code.) “ALL” indicates the average utilization across all CPUs since the last sample period. “Min”, “Max”, and “Avg” indicate a running minimum, maximum, and average of all samples since cpustat was started.

Generally, if an application’s CPU usage is fairly steady, you can run CPUstat for a bit and wait for the Max. and Avg. for the “ALL” category to stabilize, then that will tell you what the application’s peak and average % CPU utilization is.

TCBench

TCBench was born out of the need to compare VirtualGL’s performance to that of other thin client packages, some of which had frame spoiling features that couldn’t be disabled. TCBench measures the frame rate of a thin client system as seen from the client’s point of view. It does this by attaching to one of the client windows and continuously reading back a small area at the center of the window. While this may seem to be a somewhat non-rigorous test, experiments have shown that if care is taken to ensure that the application is updating the center of the window on every frame (such as in a spin animation), TCBench can produce quite accurate results. It has been sanity checked with VirtualGL’s internal profiling mechanism and with a variety of system-specific techniques, such as monitoring redraw events on the client’s windowing system.

TCBench can be found in /opt/VirtualGL/bin on Linux/Mac/Solaris or in c:\program files\VirtualGL-{version}-{build} on Windows. Run tcbench from the command line, and it will prompt you to click in the window you want to measure. That window should already have an automated animation of some sort running before you launch TCBench. Note that GLXSpheres (see below) is an ideal benchmark to use with TCBench, since GLXSpheres draws a new sphere to the center of its window on every frame.

TCBench can also be used to measure the frame rate of applications that are running on the local display, although for extremely fast applications (those that exceed 40 fps on the local display), you may need to increase the sampling rate of TCBench to get accurate results. The default sampling rate of 50 samples/sec should be fine for measuring the throughput of VirtualGL and other thin client systems.

tcbench -?

gives the relevant command line switches that can be used to adjust the benchmark time, the sampling rate, and the x and y offset of the sampling area within the window.

GLXSpheres

GLXSpheres is a benchmark which produces very similar images to NVidia’s (long discontinued) SphereMark benchmark. Back in the early days of VirtualGL’s existence, it was discovered (quite by accident) that SphereMark was a pretty good test of VirtualGL’s end-to-end performance, because that benchmark generated images with about the same amount of solid color and frequency components as the images generated by volume visualization applications.

Thus, the goal of GLXSpheres was to create an open source Unix version of SphereMark (the original SphereMark was for Windows only) completely from scratch. GLXSpheres does not use any code from the original benchmark, but it does attempt to mimic the image output of the original as closely as possible. GLXSpheres lacks some of the advanced rendering features of the original, such as the ability to use vertex arrays, but since it was primarily designed as a benchmark for VirtualGL, display lists are more than fast enough for that purpose.

GLXSpheres has some additional modes which its predecessor lacked, modes which are designed specifically to test the performance of various VirtualGL features:

Stereographic rendering (glxspheres -s)

Color index rendering (glxspheres -c)

In color index mode, GLXSpheres will draw the spheres using an 8-bit color map and will change the color map periodically.

Overlay rendering (glxspheres -o)

This is similar to color index mode, except that it renders the entire scene to a transparent overlay. This is a somewhat unrealistic test, since overlays are normally not used for rendering complex 3D scenes, but comparing this mode with color index mode demonstrates the differences in how VirtualGL handles overlays and normal PseudoColor rendering.

Immediate mode rendering (glxspheres -m)

Want to really see the benefit of VirtualGL? Run glxspheres -m over a remote X connection, then run vglrun -sp glxspheres -m over the same connection and compare. Immediate mode does not use display lists, so when immediate mode OpenGL is rendered indirectly (over a remote X connection), this causes every OpenGL command to be sent as a separate network request to the X server … on every frame. Many applications cannot use display lists, because the geometry they are rendering is dynamic, so this models how such applications might perform when displayed remotely without VirtualGL.

Interactive mode (glxspheres -i)

In interactive mode, GLXSpheres will wait to draw a frame until it receives a mouse event. Continuously dragging the mouse in the window should produce a steady frame rate, and this frame rate is a reasonable model of the frame rate that you can achieve when running interactive applications in VirtualGL. Comparing this interactive frame rate (vglrun glxspheres -i) with the non-interactive frame rate (vglrun -sp glxspheres) allows you to quantify the effect of X latency on the performance of interactive applications in a VirtualGL environment.

GLXSpheres is installed in /opt/VirtualGL/bin on Linux and Solaris VirtualGL servers. 64-bit VirtualGL packages contain both a 32-bit version (glxpheres) and a 64-bit version (glxspheres64.)

18 The VirtualGL Configuration Dialog

Several of VirtualGL’s configuration parameters can be changed on the fly once a 3D application has been started. This is accomplished by using the VirtualGL Configuration dialog, which can be popped up by holding down the CTRL and SHIFT keys and pressing the F9 key while any one of the 3D application’s windows is active. This displays the following dialog box:

You can use this dialog to adjust various image compression and display parameters in VirtualGL. Changes are reflected immediately in the application.

Image Compression (Transport)

This is a drop-down gadget with the following options:

None (X11 Transport) : equivalent to setting VGL_COMPRESS=proxy. This option can be activated at any time, regardless of which transport was active when VirtualGL started.

JPEG (VGL Transport) : equivalent to setting VGL_COMPRESS=jpeg. This option is only available if the VGL Image Transport was active when the application started.

RGB (VGL Transport) : equivalent to setting VGL_COMPRESS=rgb. This option is only available if the VGL Image Transport was active when the application started.

DPCM (Sun Ray Transport) : equivalent to setting VGL_COMPRESS=sr. This option is only available if the Sun Ray Image Transport was active when the application started.

RGB (Sun Ray Transport) : equivalent to setting VGL_COMPRESS=srrgb. This option is only available if the Sun Ray Image Transport was active when the application started.

See Section 19.1 for more information about the VGL_COMPRESS configuration option and its various parameters.

Chrominance Subsampling

This drop-down gadget is active only when using JPEG or Sun Ray DPCM compression. It has the following options:

Grayscale : equivalent to setting VGL_SUBSAMP=gray. Available only with JPEG compression.

1X : equivalent to setting VGL_SUBSAMP=1x

2X : equivalent to setting VGL_SUBSAMP=2x

4X : equivalent to setting VGL_SUBSAMP=4x

8X : equivalent to setting VGL_SUBSAMP=8x. Available only with Sun Ray DPCM compression.

16X : equivalent to setting VGL_SUBSAMP=16x. Available only with Sun Ray DPCM compression.

See Section 19.1 for more information about the VGL_SUBSAMP configuration option and its various parameters.

JPEG Image Quality

This slider gadget is active only when using JPEG compression. It is the equivalent of setting VGL_QUAL. See Section 19.1 for more information about the VGL_QUAL configuration option.

Send Lossless Frame During Periods of Inactivity

This toggle button is the equivalent of setting VGL_PROGRESSIVE. It is active only when using Sun Ray DPCM compression. See Section 19.1 for more information about the VGL_PROGRESSIVE configuration option.

Connection Profile

This drop-down gadget is active only if the VGL Image Transport was active when the application started. It has the following options:

Low Qual (Wide-Area Network) : Sets the image compression type to JPEG (VGL Transport), sets the Chrominance Subsampling to 4X, and sets the JPEG Image Quality to 30.

Medium Qual : Sets the image compression type to JPEG (VGL Transport), sets the Chrominance Subsampling to 2X, and sets the JPEG Image Quality to 80.

High Qual (High-Speed Network) : Sets the image compression type to JPEG (VGL Transport), sets the Chrominance Subsampling to 1X, and sets the JPEG Image Quality to 95.

Gamma Correction Factor

This floating point input gadget is the equivalent of setting VGL_GAMMA. If using a gamma-corrected visual (Sparc clients only), then this gadget has no effect. Otherwise, it enables VirtualGL’s internal gamma correction system with the specified gamma correction factor. See Section 19.1 for more information about the VGL_GAMMA configuration option.

Frame Spoiling

This toggle button is the equivalent of setting VGL_SPOIL. See Section 17.2 and Section 19.1 for more information about the VGL_SPOIL configuration option.

Interframe Comparison

This toggle button is the equivalent of setting VGL_INTERFRAME. See Section 19.1 for more information about the VGL_INTERFRAME configuration option.

Stereographic Rendering Method

This drop-down gadget has the following options:

Send Left Eye Only : equivalent to setting VGL_STEREO=left.

Send Right Eye Only : equivalent to setting VGL_STEREO=right

Quad-Buffered (if available) : equivalent to setting VGL_STEREO=quad

Anaglyphic (Red/Cyan) : equivalent to setting VGL_STEREO=rc

See Section 19.1 for more information about the VGL_STEREO configuration option and its various parameters.

Limit Frames/second

This floating point input gadget is the equivalent of setting VGL_FPS. See Section 19.1 for more information about the VGL_FPS configuration option.

You can set the VGL_GUI environment variable to change the key sequence used to pop up the VirtualGL Configuration dialog. If the default of CTRL-SHIFT-F9 is not suitable, then set VGL_GUI to any combination of ctrl, shift, alt, and one of f1, f2,..., f12 (these are not case sensitive.) For example:

export VGL_GUI=CTRL-F9

will cause the dialog box to pop up whenever CTRL-F9 is pressed.

To disable the VirtualGL dialog altogether, set VGL_GUI to none.

19 Advanced Configuration

19.1 Server Settings

You can control the operation of the VirtualGL faker in four different ways. Each method of configuration takes precedence over the previous method:

1. Setting a configuration environment variable globally (for instance, in /etc/profile)
2. Setting a configuration environment variable on a per-user basis (for instance, in ~/.bashrc)
3. Setting a configuration environment variable only for the current shell session (for instance, export VGL_XXX={whatever})
4. Passing a configuration option as an argument to vglrun. This effectively overrides any previous environment variable setting corresponding to that configuration option.

Description

When using the VGL Image Transport, VGL_CLIENT should be set to the hostname or IP address of the machine on which vglclient is running. When using the Sun Ray Image Transport, VGL_CLIENT should be set to the hostname or IP address of the Sun Ray server. Normally, VGL_CLIENT is set automatically by the vglconnect or vglrun script, so don’t override it unless you know what you’re doing.

Description

proxy = Send images uncompressed using the X11 Image Transport. This is useful when displaying to a local X server or X proxy (see Section 9.1.)

jpeg = Compress images using JPEG and send using the VGL Image Transport. This is useful when displaying to a remote X server (see Chapter 8.)

rgb = Encode images as uncompressed RGB and send using the VGL Image Transport. This is useful when displaying to a remote X server or X proxy across a very fast network (see Section 9.2.)

sr = Compress images using the Sun Ray default compression method (DPCM) and send using the Sun Ray Image Transport. This requires that the proprietary Sun Ray plugin be installed on the VirtualGL server. (see Chapter 11.)

srrgb = Encode images as uncompressed RGB and send using the Sun Ray Image Transport. This requires that the proprietary Sun Ray plugin be installed on the VirtualGL server (see Chapter 11.)

If this option is not specified, then the default is set as follows:

If the X server is a Sun Ray server and the Sun Ray plugin is installed on the VirtualGL server, then VGL will default to using sr compression. VGL will fall back to using proxy compression if, for any given frame, it is unable to send the frame using the Sun Ray Image Transport. This could occur if, for example, the Sun Ray client is on a network that is not visible to the VirtualGL server.

If the X server is not a Sun Ray server but the DISPLAY environment variable begins with : or unix:, then VirtualGL assumes that the X display connection is local and it defaults to using proxy compression. Otherwise, it defaults to jpeg compression.

Description

If the VirtualGL server has multiple 3D graphics cards and you want the OpenGL rendering to be redirected to a display other than :0, then you can set VGL_DISPLAY=:1.0 or whatever. This could be used, for instance, to support many application instances on a beefy multi-pipe graphics server.

GLP mode (Solaris/Sparc only):

Setting this option to glp will enable GLP mode and use the first framebuffer device listed in /etc/dt/config/GraphicsDevices to perform 3D rendering. You can also set this option to the pathname of a specific GLP device (example: /dev/fbs/jfb0.) See Section 6.1 for more details.

Description

This option prevents VirtualGL from sending frames at a rate faster than the specified limit. It can be used, for instance, as a crude way to control network bandwidth or CPU usage in multi-user environments where those resources are constrained.

If frame spoiling is disabled, then this effectively limits the server’s 3D rendering frame rate as well.

Description

“Gamma” refers to the relationship between the intensity of light which your computer’s monitor is instructed to display and the intensity which it actually displays. The curve is an exponential curve of the form Y = X^G, where X is between 0 and 1. G is called the “gamma” of the monitor. PC monitors and TV’s usually have a gamma of around 2.2.

Some of the math involved in 3D rendering assumes a linear gamma (G = 1.0), so technically speaking, 3D applications will not display with mathematical correctness unless the pixels are “gamma corrected” to counterbalance the non-linear response curve of the monitor. But some systems do not have any form of built-in gamma correction, and thus the applications developed for such systems have usually been designed to display properly without gamma correction. Gamma correction involves passing pixels through a function of the form X = W^1/G, where G is the “gamma correction factor” and should be equal to the gamma of the monitor. So the final output is Y = X^G = (W^1/G)^G = W, which describes a linear relationship between the intensity of the pixels drawn by the application and the intensity of the pixels displayed by the monitor.

VGL_GAMMA=1 or vglrun +g : Enable gamma correction with default settings

This option tells VirtualGL to enable gamma correction using the best available method. If VirtualGL is remotely displaying to a Solaris/Sparc X server which has gamma-corrected X visuals, then VGL will attempt to assign one of these visuals to the application. This causes the 3D output of the application to be gamma corrected by the factor specified in fbconfig on the client machine (default: 2.22.) Otherwise, if the X server does not have gamma-corrected X visuals or if the gamma-corrected visuals it has do not match the application’s needs, then VirtualGL performs gamma correction internally and uses a default gamma correction factor of 2.22. This option emulates the default behavior of OpenGL applications running locally on Sparc machines.

VGL_GAMMA=0 or vglrun -g : Disable gamma correction

This option tells VGL not to use gamma-corrected visuals, even if they are available on the X server, and disables VGL’s internal gamma correction system as well. This emulates the default behavior of OpenGL applications running locally on Linux or Solaris/x86 machines.

VGL_GAMMA={g} or vglrun -gamma {g} : Enable VGL’s internal gamma correction system with a gamma correction factor of {g}

If VGL_GAMMA is set to an arbitrary floating point value, then VirtualGL performs gamma correction internally using the specified value as the gamma correction factor. You can also specify a negative value to apply a “de-gamma” function. Specifying a gamma correction factor of G (where G < 0) is equivalent to specifying a gamma correction factor of -1/G.

Description

Normally, VirtualGL loads the first OpenGL dynamic library that it finds in the dynamic linker path (usually /usr/lib/libGL.so.1, /usr/lib64/libGL.so.1, or /usr/lib/64/libGL.so.1.) You can use this setting to explicitly specify another OpenGL dynamic library to load.

You shouldn’t need to muck with this unless something doesn’t work. However, this setting is necessary when using VirtualGL with Chromium.

Description

VirtualGL will normally monitor an application’s X event queue and pop up the VirtualGL Configuration dialog whenever CTRL-SHIFT-F9 is pressed. In the event that this interferes with a key sequence that the application is already using, then you can redefine the key sequence used to pop up the VirtualGL Configuration dialog by setting VGL_GUI to some combination of shift, ctrl, alt, and one of f1, f2, ..., f12. You can also set VGL_GUI to none to disable the configuration dialog altogether. See Chapter 18 for more details.

Description

The VGL and Sun Ray Image Transports will normally compare each frame with the previous frame and send only the portions of the image which have changed. Setting VGL_INTERFRAME to 0 disables this behavior.

You shouldn’t need to disable interframe comparison except in rare situations. This setting was introduced in order to work around a specific interaction issue between VirtualGL and Pro/ENGINEER v3. See Section 15 for more information.

When using the VGL Image Transport, interframe comparison is affected by the VGL_TILESIZE option

Description

Setting this environment variable to the pathname of a log file on the VirtualGL server will cause VirtualGL to redirect all of its messages (including profiling and trace output) to the specified log file rather than to stderr.

Description

The VGL Image Transport can divide the task of compressing each frame among multiple server CPUs. This might speed up the overall throughput in rare circumstances where the server CPUs are significantly slower than the client CPUs.

VirtualGL will not allow more than 4 processors total to be used for compression, nor will it allow you to set this parameter to a value greater than the number of processors in the system.

Multi-threaded compression is affected by the VGL_TILESIZE option

Description

The connection port for the VGL Image Transport is normally determined by reading an X property that vglclient stores on the X server, so don’t override this unless you know what you’re doing.

Description

If profiling output is enabled, then VirtualGL will continuously benchmark itself and periodically print out the throughput of various stages in its image pipelines.

See Chapter 17 for more details.

Description

When Sun Ray DPCM compression is being used, enabling this option causes the Sun Ray Image Transport to send a lossless (RGB) frame during periods of inactivity. This is useful in environments where both image quality and performance are critical. With progressive mode enabled, the image quality for the Sun Ray compressor can be set to a fairly low value to speed up rotate/pan/zoom operations, then when the rotate/pan/zoom is completed, VirtualGL will send a lossless frame that can be analyzed by the user in more detail.

Description

In digital images, “frequency” refers to how quickly the color changes between light and dark as you move either horizontally or vertically in the image. Images with very sharp, bright features on a dark background, for instance, consist of both low- and high-frequency components, whereas images with smooth transitions between neighboring pixels contain only low-frequency components. JPEG compression works by breaking down the image into its constituent frequencies and then throwing out the highest of these frequencies. The JPEG image “quality” determines which frequencies are thrown out. A JPEG quality of 1 throws out all but the lowest frequencies and thus produces a very impressionistic, but generally not very useful, compressed image. A JPEG quality of 100 retains all frequencies in the original image (but, due to roundoff errors, is still not completely lossless.)

Because the human eye usually can’t detect the highest frequencies in the image, and often because the image lacks those high-frequency elements to begin with, a sufficiently high JPEG quality setting can produce a “perceptually lossless” image. A “perceptually lossless” image contains a small amount of mathematical error vs. the original image, but this error is so small that the human visual system cannot distinguish it (under normal circumstances.) The threshold quality level at which JPEG compression becomes perceptually lossless is different for each image, but experiments with various visual difference benchmarks (such as HDR-VDP) suggest that a JPEG quality of 95 is sufficient to guarantee perceptual losslessness in the types of applications (volume visualization apps, in particular) where image quality is critical. As with any benchmarks, Your Mileage May Vary. If quality is of paramount concern, consider setting the JPEG quality to 100 or using RGB encoding.

Description

On rare occasions, it might be desirable to have VirtualGL redirect OpenGL rendering from an application into a Pbuffer but not automatically read back and send the rendered pixels. Some applications have their own mechanisms for reading back the buffer, so setting VGL_READBACK=0 disables VirtualGL’s readback mechanism and prevents duplication of effort.

This feature was developed initially to support running ParaView in parallel using MPI. ParaView/MPI normally uses MPI processes 1 through N as rendering servers, each drawing a portion of the geometry into a separate window on a separate X display. ParaView reads back these server windows and composites the pixels into the main application window, which is controlled by MPI process 0. By creating a script which passes a different value of VGL_DISPLAY and VGL_READBACK to each MPI process, it is possible to make all of the ParaView server processes render to off-screen buffers on different graphics cards while preventing VirtualGL from displaying any pixels except those generated by process 0.

Description

By default, VirtualGL will drop frames so as not to slow down the rendering rate of the server’s graphics engine. This should produce the best results with interactive applications, but frame spoiling should be turned off when running benchmarks or other non-interactive applications. Turning off frame spoiling will force one frame to be sent to the client on every end-of-frame event, and thus the frame rate reported by OpenGL benchmarks will accurately reflect the frame rate of VirtualGL’s image pipeline (though, in X proxy environments, this may still not accurately reflect the frame rate seen by the user. See Section 17.2.) Disabling frame spoiling also prevents non-interactive applications from wasting graphics resources by rendering frames that will never be seen. With frame spoiling turned off, the 3D rendering pipeline behaves as if it is fill-rate limited to about 30 or 40 Megapixels/second, the maximum throughput of the VirtualGL system on current CPUs.

Description

Enabling this option causes the VGL Image Transport to be tunneled through a secure socket layer (SSL) (see Section 8.3.)

Description

left = When an application renders a stereo frame, send only the left eye buffer

right = When an application renders a stereo frame, send only the right eye buffer

quad = Attempt to use quad-buffered stereo, which will result in a pair of images being sent to the VirtualGL Client on every frame. If quad-buffered stereo is not available, either because the client or the image transport does not support it, then fall back to using anaglyphic stereo. Quad-buffered stereo requires the VGL Image Transport, and it also requires that client support OpenGL and have a 3D accelerator that supports stereo rendering.

rc = Use Red/Cyan (anaglyphic) stereo, even if quad-buffered is available

See Chapter 16 for more details.

Description

When an image is compressed using JPEG or using Sun Ray DPCM compression, each pixel in the image is first converted from RGB (Red/Green/Blue) to YUV. An RGB pixel has three values that specify the amounts of red, green, and blue that make up the pixel’s color. A YUV pixel has three values that specify the overall brightness of the pixel (Y, or “luminance”) and the overall color of the pixel (U and V, or “chrominance”.)

Since the human eye is less sensitive to changes in color than it is to changes in brightness, the chrominance components for some of the pixels can be discarded without much noticeable loss in image quality. This technique, called “chrominance subsampling”, significantly reduces the size of the compressed image.

1x = no chrominance subsampling

2x = discard the chrominance components for every other pixel along the image’s X direction (this is also known as “4:2:2” or “2:1” subsampling.) All else being equal, 2x subsampling generally reduces the image size by about 20-25% when compared to no subsampling.

4x = discard the chrominance components for every other pixel along both the X and Y directions of the image (this is also known as “4:2:0” or “2:2” subsampling.) All else being equal, 4x subsampling generally reduces the image size by about 35-40% when compared to no subsampling.

8x = discard the chrominance components for 3 out of every 4 pixels along the image’s X direction and half the pixels along the image’s Y direction (this is also known as “4:1:0” or “4:2” subsampling.) This option is available only with Sun Ray DPCM compression.

16x = discard the chrominance components for 3 out of every 4 pixels along both the X and Y directions of the image (this is also known as “4:4” subsampling.) This option is available only with Sun Ray DPCM compression.

gray = discard all chrominance components. This is useful when running applications (such as medical visualization applications) that are already generating grayscale images. This option is available only with JPEG compression.

Subsampling artifacts are less noticeable with volume data, since it usually only contains 256 colors to begin with. But narrow, aliased lines and other sharp features on a black background will tend to produce very noticeable artifacts when subsampling is enabled.

The Axis Indicator from a Popular Visualization App displayed with 1x, 2x, and 4x subsampling (respectively):

Description

Normally, VirtualGL’s operation is asynchronous from the point of view of the application. The application swaps the buffers or calls glFinish() or glFlush() or glXWaitGL(), and VirtualGL reads back the framebuffer and sends the pixels to the client’s display … eventually. This will work fine for the vast majority of applications, but it does not strictly conform to the GLX spec. Technically speaking, when an application calls glXWaitGL() or glFinish(), it is well within its rights to expect the 3D image to be immediately available in the X window. Fortunately, very few applications actually do expect this, but on rare occasions, an application may try to use XGetImage() or other X11 functions to obtain a bitmap of the pixels that were rendered by OpenGL. Enabling VGL_SYNC is a somewhat extreme measure that may be needed to make such applications work properly. It was developed initially as a way to pass the GLX conformance suite (conformx, specifically), but at least one commercial application is known to require it as well (see Application Recipes.)

When VGL_SYNC is enabled, every call to glFinish(), glXWaitGL(), and glXSwapBuffers() will cause the contents of the server’s framebuffer to be read back and synchronously drawn into the application’s window using the X11 Image Transport and no frame spoiling. The call to glFinish(), glXWaitGL(), or glXSwapBuffers() will not return until VirtualGL has verified that the pixels have been delivered into the application’s window. As such, this mode can have potentially dire effects on performance when used with a remote X server. It is thus strongly recommended that VGL_SYNC be used only in conjunction with an X proxy (such as TurboVNC) running on the same server as VirtualGL.

Description

Normally, the VGL Image Transport will divide an OpenGL window into equal-sized square tiles, compare each tile vs. the same tile in the previous frame, and compress & send only the tiles which have changed (assuming interframe comparison is enabled.) The VGL Image Transport will also divide up the task of compressing these tiles among the available CPUs in a round robin fashion, if multi-threaded compression is enabled (see VGL_NPROCS.)

There are several tradeoffs that must be considered when choosing a tile size:

Smaller tile sizes:

• Better parallel scalability
• Worse compression efficiency
• Better inter-frame optimization
• Worse network efficiency

Larger tile sizes:

• Worse parallel scalability
• Better compression efficiency
• Worse inter-frame optimization
• Better network efficiency

Smaller tiles can more easily be divided up among multiple CPUs, but they compress less efficiently (and less quickly) on an individual basis. Using larger tiles can reduce traffic to the client by allowing the server to send only one frame update instead of many. But on the flip side, using larger tiles decreases the chance that a tile will be unchanged from the previous frame.

256x256 was chosen as the default because, in experiments, it provided the best balance between scalability and efficiency on the platforms that VirtualGL supports.

Description

When tracing is enabled, VirtualGL will log all calls to the GLX and X11 functions it is intercepting, as well as the arguments, return values, and execution times for those functions. This is useful when diagnosing interaction problems between VirtualGL and a particular OpenGL application.

Description

When in verbose mode, VirtualGL will reveal some of the decisions it makes behind the scenes, such as which code path it is using to compress images, which type of X11 drawing it is using, etc. This can be helpful when diagnosing performance problems.

Description

Normally, VirtualGL loads the first X11 dynamic library that it finds in the dynamic linker path (usually /usr/lib/libX11.so.?, /usr/lib/64/libX11.so.?, /usr/X11R6/lib/libX11.so.?, or /usr/X11R6/lib64/libX11.so.?.) You can use this setting to explicitly specify another X11 dynamic library to load.

You shouldn’t need to muck with this unless something doesn’t work.

Description

Some applications expect XServerVendor() to return a particular value, which the application (sometimes erroneously) uses to figure out whether it’s running locally or remotely. This setting allows you to fool such applications into thinking they’re running on a “local” X server rather than a remote connection.

Description

Setting VGL_ZOOM_X=2 causes the Sun Ray Image Transport to discard every other pixel along the X direction of the image. Setting VGL_ZOOM_Y=2 does the same thing for the Y direction of the image. This differs from VGL_SUBSAMP in that VGL_SUBSAMP discards only luminance components from the pixels it subsamples. VGL_ZOOM_*, on the other hand, discards the entire pixels. The result is extremely grainy, so this option is generally only useful in conjunction with VGL_PROGRESSIVE.

19.2 Client Settings

These settings control the VirtualGL Client, which is used only with the VGL Image Transport. vglclient is normally launched automatically from vglconnect and should not require any further configuration except in exotic circumstances. These settings are meant only for advanced users or those wishing to build additional infrastructure around VirtualGL.

Description

If the client machine has a 3D accelerator, then it may be faster to draw pixels using OpenGL than using 2D (X11) commands. This is particularly true of many 3D accelerators available for the Sparc platform, since they are able to draw images using 24-bit pixels instead of the 32-bit pixels required by the X server.

Description

The default behavior for vglclient is to first try listening on port 4242, to maintain backward compatibility with VirtualGL v2.0.x. If port 4242 is not available, then vglclient will try to find a free port in the range of 4200-4299. If none of those ports is available, then vglclient will request a free port from the operating system.

Passing this argument to vglclient circumvents the automatic behavior described above and causes vglclient to listen only on the specified TCP port. Don’t do this unless you know what you’re doing.

Description

If profiling output is enabled, then VirtualGL will continuously benchmark itself and periodically print out the throughput of various stages in its image pipelines.

See Chapter 17 for more details.

Description

The default behavior for vglclient is to first try listening on port 4243, to maintain backward compatibility with VirtualGL v2.0.x. If port 4243 is not available, then vglclient will try to find a free port in the range of 4200-4299. If none of those ports is available, then vglclient will request a free port from the operating system.

Passing this argument to vglclient circumvents the automatic behavior described above and causes vglclient to listen only on the specified TCP port. Don’t do this unless you know what you’re doing.

Description

When in verbose mode, VirtualGL will reveal some of the decisions it makes behind the scenes, such as which code path it is using to decompress images, which type of X11 drawing it is using, etc. This can be helpful when diagnosing performance problems.