[Bug 1280665] Re: libsdl1.2 always uses backingstore which causes tearing in modern X servers

[Timo Jyrinki]

** Description changed:

+ [Impact]
+ Tearing in SDL applications regardless of vsync setting.
+ 
+ [Test Case]
+ Use eg. XBMC to play any video, or a particular video that more easily shows up the tearing of the images.
+ 
+ [Regression Potential]
+ This is a regression fix in itself, and restores old behavior.
+ 
+ ---
+ 
+ Fedora 21 has a similar patch applied
+ https://bugzilla.redhat.com/show_bug.cgi?id=1073057
+ 
  libsdl1.2 always enables backingstore when it is present in the X
  server. For modern X servers, backingstore is implemented by redirecting
  through the composite extension. This causes tearing on SDL applications
  such as xbmc because the redirected rendering is not guaranteed to be
  synchronized.
  
  A discussion of the problem by Nvidia is here:
  https://devtalk.nvidia.com/default/topic/679688/linux/tearing-in-sdl-1-2
  -apps-unless-composite-extension-is-completely-
  disabled-/post/4111287/#4111287
  
  The upstream bug is here:
  https://bugzilla.libsdl.org/show_bug.cgi?id=2383
  
  I have a patch that restores a check for the SDL_VIDEO_X11_BACKINGSTORE
  environment variable before trying to enable backingstore.

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https://bugs.launchpad.net/bugs/1280665

Title:
  libsdl1.2 always uses backingstore which causes tearing in modern X
  servers

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