On 11/09/2015 01:15 PM, Dave Airlie wrote:
On 10 November 2015 at 00:30, Roland Scheidegger <srol...@vmware.com> wrote:
Am 09.11.2015 um 04:44 schrieb 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.
I don't really understand all this interface stuff, however it feels
wrong to me that we have to care in the driver for something which you
say is totally bogus. Couldn't that be handled outside? Albeit I don't
really understand what exactly happens in the first place.
Well the bug is piglit runs tests without mapping the window. On DRI2
this works as we have the fake front buffer, so reading the front doesn't
require content on the screen. However it's really undefined behaviour for GL.
Now with drisw you use GetImage/PutImage to get things from the real front
buffer. However if the window is never mapped, these will return BadMatch,
and things fall over. However we have real apps wanting proper front buffer
interactions, and we have piglit wanting the undefined behaviour.
The old xlib/swrast code has an X error handler to catch failing
XGetImage calls. We probably need something like that. See
xm_buffer.c's xmesa_MapRenderbuffer().
It also sounds like the piglit tests in question need to be fixed somehow.
-Brian
I think I'll decide in favour of the former, but it might be a bit of a shock to
people who run piglit runs and things start regressing.
Dave.
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