Problems
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Chapter 4. Problems

The whole Composite extension is quite new. It may cause several problems and even crash X, so it is strongly suggested to not even enable the Composite extension in Xorg.conf on mission critical production systems. If you however can risk a slightly more unstable system, it's certainly nice to have some eye candy around.

In this case you may notice some glitches. Here are some common problems - and workarounds:

4.1. I have X.org 6.8.x, but kompmgr fails to start
4.2. Ok, kompmgr works, but it's horribly slow
4.3. After enabling the Composite extension, I cannot run any GLX applications anymore. I've got an NVIDIA card.
4.4. I wanted to play a game using SDL (but not GL), say scummvm, but when the compmgr is active, all I can see is a shadow!
4.5. Application XXX refuses to start after enabling the Composite extension.
4.6. I try to watch a video, but only see artefacts in the Video Window.
4.1.

I have X.org 6.8.x, but kompmgr fails to start

You need to explicitly enable the Composite extension, add a new Section to /etc/X11/XorgConfig:

Section "Extensions"
   Option "Composite" "Enable"
EndSection
4.2.

Ok, kompmgr works, but it's horribly slow

If supported by your GPU (mainly NVIDIA™, and somewhat by ATI cards), first make sure you activated the Render acceleration

Section "Device"
....
....
Option     "RenderAccel" "true"
....
....
EndSection

If it's still slow, you can try to adjust your memory usage. Either decrease you screen depth (e.g. from 24 to 16) or lower your resolution (e.g. from 1280x1024 to 1024x768).

Please notice that the currently limiting factor for the Composite extension seems to be the CPU cache size.

4.3.

After enabling the Composite extension, I cannot run any GLX applications anymore. I've got an NVIDIA™ card.

To prevent some problems, NVIDIA™ deactivated the GLX support when Coposite is active. Reactivating is possible, but may cause problems on some kernel/driver/GPU combinations.

Section "Device"
....
....
Option  "AllowGLXWithComposite" "true"
....
....
EndSection
4.4.

I wanted to play a game using SDL (but not GL), say scummvm, but when the compmgr is active, all I can see is a shadow!

This is a problem with the PictType reported by SDL.

Workaround:

Instead of calling scummvm directly, call
SDL_VIDEO_X11_VISUALID=0x24 scummvm This will tell SDL to
use a supported format and you can play as ever. 
4.5.

Application XXX refuses to start after enabling the Composite extension.

Application YYY breaks X after enabling the Composite extension.

Application ZZZ looks weird after activating the composite manager.

The Composite extension is still experimental.

Workaround:

Instead of calling appName directly, call XLIB_SKIP_ARGB_VISUALS=1 appName

Applications that are known to cause problems:

  • All gtk1 applications (e.g. gmplayer, xmms, gaim) - failing startup or look unusable weird or crash X

  • KuickShow - displays only a black frame

  • QtDesigner - crashes X

  • Kopete - crashes X

  • Kolf - crashes X

4.6.

I try to watch a video, but only see artefacts in the Video Window.

You're using “xv” as video backend. This is the overlay mode, where the video content is written directly into the video card memory, bypassing X. Therefore the window seems to be static (colored background) and is not updated by the damage extension.

There will hopefully be a fix for this in the future. Currently I had the best results using Xine but displaying translucent videos isn't fast anyway.

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