[Mesa-dev] [Bug 98846] triangle clipping causes wrong vertex's attribute to be broadcasted for flat interpolation

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98846

Zebediah Figura <z.figura12 at gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |z.figura12 at gmail.com

--- Comment #2 from Zebediah Figura <z.figura12 at gmail.com> ---
This also affects softpipe and llvmpipe. I'm not familiar with mesa, but I
think there are multiple places that do the wrong thing. For example,
do_clip_tri() in src/gallium/auxiliary/draw/draw_pipe_clip.c gets passed the
vertices in winding order, but it doesn't take that into account when
determining provoking vertex.

If this should be split off to a separate bug, then I'll do so.

This causes failures in Wine's conformance test suite, since we use
GL_FIRST_VERTEX_CONVENTION universally, and test flat shading with
GL_TRIANGLESTRIP and some vertices slightly clipped outside of the viewport.
Since our test suite is run in a virtual machine, it uses llvmpipe, and so is
affected by this bug.

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