On Thu, 05 Jun 2003 16:51:27 -0600 Brian Paul <[EMAIL PROTECTED]> wrote:
Felix Kühling wrote:
Hi,
even with LIBGL_SYNC_REFRESH I get bad tearing with quake2. I looked into the source a bit and now I'm scratching my head about this question: Does waiting for a vblank do anything useful if you havn't flushed the 3D hardware graphics pipeline before? I believe the driver should call something equivalent to glFinish before driWaitForVBlank if LIBGL_SYNC_REFRESH is set.
Further in case of a non-zero swap interval you will throttle the frame rate but there is no guarantee that the swap will occur during a retrace if the application or the driver havn't called glFinish. I guess applications explicitly using swap intervals are aware of that. But LIBGL_SYNC_REFRESH is supposed to work for applications that don't even know they are waiting for a vblank. So the driver should call glFinish for them.
I hope I'm not completely off with my theories ;-)
When glXSwapBuffers is called, the rendering context currently bound to the window (if any) is flushed (ala glFinish) automatically. Then, glXSwapBuffers should wait for the end of the screen refresh before swapping.
From the glXSwapBuffers manpage:
glXSwapBuffers performs an implicit glFlush before it returns. Subse- quent OpenGL commands may be issued immediately after calling glXSwap- Buffers, but are not executed until the buffer exchange is completed.
glFlush is not the same as glFinish.
I knew it was one or the other and just took a guess without looking it up.
The radeon and r200 drivers can have up to one frame in the hardware rendering pipeline when the pageflip or buffer copying commands are sent to the hardware (they are pipelined as well). The frame throttling code in radeonWaitForFrameCompletion makes sure that it doesn't get more than one frame as that would introduce too much latency in interactive applications.
That said, I don't know why you're seeing tearing.
I added this to radeon_ioctl.c in radeonPageFlip just before the call to driWaitForVBlank:
if ((rmesa->vblank_flags & VBLANK_FLAG_SYNC)) radeonFinish (rmesa->glCtx);
Now the tearing is gone.
Maybe Ian can double-check that and check it in?
-Brian
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