[Piglit] New test for partial blits after a buffer swap

[Paul Berry]

On 29 October 2013 14:46, Eric Anholt <eric at anholt.net> wrote:

> Federico Mena Quintero <federico.mena.lists at gmail.com> writes:
>
> > Hello, everyone,
> >
> > Attached is a new test for piglit which exposes a bug in Mesa's
> > software rendering (and another bug in hardware rendering, but that's
> > not its main purpose).
> >
> > The bug is as follows.  With software rendering, after doing a buffer
> > swap, glBlitFrameBufferEXT() appears to to copy the whole framebuffer
> > instead of just the specified region.  This breaks clutter and cogl,
> > since they keep track of a dirty region themselves, and they use blits
> > instead of full buffer swaps to avoid updating the whole display on
> > every frame unnecessarily.
> >
> > What is happening is actually a bit more complicated.
> > glBlitFrameBufferEXT()'s basic machinery works correctly, but if there
> > has been a buffer swap before it, the following happens:
>
> Hah.  Apparently the problem is you're hitting this line of
> platform_x11.c in EGL:
>
>    /* FIXME: Does EGL support front buffer rendering at all? */
>

FYI, we discussed this issue back in May but didn't really come to a clear
consensus of what we wanted to do about it:
http://lists.freedesktop.org/archives/mesa-dev/2013-May/040059.html.  (Note
that the replies happened in July so the mesa-dev archives don't thread
them well.  See
http://lists.freedesktop.org/archives/mesa-dev/2013-June/subject.html#40129for
the replies.)
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