[Bug 28771] Vsync always on

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=28771

--- Comment #11 from Alex Deucher <agd5f at yahoo.com> 2010-07-18 01:10:40 PDT ---
(In reply to comment #10)
> 
> What is the real solution and why is this patch needed in DDX?

The real solution to what?  The various GLX vsync/vblank extensions basically
just expose frame counters and vertical retrace events to applications so they
can use them for synchronization.  They have nothing to do with tearing
prevention directly.  The code in the ddx you are asking about has nothing to
do with the GLX vsync/vblank extensions; it is there to prevent tearing on GL
buffer swaps.  The variable should probably have been called vline_wait rather
than vsync.  What the code does is forces the GPU to wait until the current
scanline is past the area that will be updated by the swap before doing the
swap blit.  It's the same method used by Xv to prevent tearing when rendering
to the front buffer.

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