[Piglit] [PATCH 4/5] Test interaction between fast color clears and glXSwapBuffers.

[Paul Berry]

On 22 May 2013 16:20, Eric Anholt <eric at anholt.net> wrote:

> Paul Berry <stereotype441 at gmail.com> writes:
> > +/**
> > + * \file glx-fast-color-clear.c
> > + *
> > + * On implementations that support fast color clear (e.g. i965/gen7+),
> > + * verify that memory writes that were deferred as the result of a
> > + * fast clear are properly resolved at the time of glXSwapBuffers.
> > + *
> > + * We can't use glReadPixels() to do this, since glReadPixels() also
> > + * does a resolve, so instead we read the contents of the front buffer
> > + * directly from X after the swap.
> > + *
> > + * Since glXSwapBuffers doesn't actually perform the swap (it simply
> > + * queues it to happen later), the test needs to wait for the swap to
> > + * occur before reading the front buffer.  If the implementation
> > + * supports it, we do so using the GLX_INTEL_swap_event extension.
> > + * Otherwise we sleep for 1 second to give time for the swap to occur.
> > + */
>
> It seems to me like the test shouldn't have to do this. Particularly
> this text:
>
> "glXSwapBuffers is in the OpenGL stream if and only if the display and
> drawable are those belonging to the calling thread’s current context;
> otherwise it is in the X stream."
>
> and
>
> "Subsequent OpenGL commands can be issued immediately, but will not be
> executed until the buffer swapping has completed, typically during
> vertical retrace of the display monitor."
>
> Our display and drawable are the calling thread's current context, so
> the subsequent ReadPixels should be serialized against the result of the
> swap.  I think this is a bug in the X Server, and maybe this is what's
> affecting those other frontbuffer-reading tests.
>

But this test doesn't use ReadPixels (see the documentation above); it uses
xcb_image_get().  Does that change your opinion about whether this is an X
server bug?


>
> Patch 1-3 and 5 are:
>
> Reviewed-by: Eric Anholt <eric at anholt.net>
>
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