[Mesa-dev] soft/llvmpipe front buffer access and piglit regressions

[Dave Airlie]

So it appears my patch to enable front buffer access on soft/llvmpipe
causes some piglit regressions. However these are due to piglit having
undefined behaviour where it doesn't create a window but has tests
requiring a front buffer. The new code does an XGetImage on the front
buffer and when it fails all sorts of bad things tend to happen. I
don't think there is a way to check if we have a window mapped inside
Mesa to avoid this path.

swrast suffers from the same failure pattern in a number of tests when
run with -auto.

I'm not sure what to do here, the patch is making the driver
conformant and is fixing a missing
feature being used by OpenGL apps (gtk).

I can probably make it fail more gracefully (llvmpipe deadlocks on the
Xlib error path inside it's rasteriser threads), but I'm not sure I
want to go back to the old behaviour just to satisfy piglit's
requirement to do undefined things.

Dave.