[Bug 42435] Suspected loss of varyings between shaders

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=42435

--- Comment #4 from Alexander Sabourenkov <screwdriver at lxnt.info> 2011-11-01 15:27:29 PDT ---
The workaround did not help r600g. Same black screen. In addition, the non-llvm
swrast draws point sprites 60 pixels in size instead of requested 16 (my
original shaders get texture sub-image size via varyings too), plus it draws
solid-black-textured point sprites as single pixels. r600c (as of Oct 27 git,
just before being axed) works though.

Not knowing whether any given black screen is a bug, or legitimate undefined
behaviour that just happens to work on some other renderer is driving me mad.

I managed to cut down the test case to bare minimum.

Usage:

./testbed <shaderset> <mesadriver>

shaderset is either "working" or "failing" - loads similarly named shaders.

"working" shader set does texture sampling in fragment shader
"failing" shader set does texture sampling in vertex shader and passes
the color as a varying vec4.

mesadriver is:
hw - default, LIBGL_ALWAYS_SOFTWARE and LIBGL_DRIVERS_PATH unset.
hw-alt - use .so from dri-alternates (x64-86 hardcoded, sorry).
sw - LIBGL_ALWAYS_SOFTWARE=y
sw-alt - as above, but use .so from dri-alternates.

For the Oct 27 git these map to r600g, r600c, swrast, llvmpipe on my box.

Of those:

"failing" llvmpipe - works as intended, vertical colored bars (composed of
16x16 point sprites), one sprite is dark green - left unpainted intentionally.
"working" llvmpipe - same (ok)
"failing" DRI - ok
"working" DRI - ok
"failing" r600g - all sprites black 
"working" r600g - all sprites black 
"failing" old-swrast  - single pixels instead of 16x16, but looks like color is
right
"working" old-swrast  - same as "failing"

The hardware is rv770 9440.

I'd say there's a problem with r600g and a different one with old swrast.

There's also intermittent display corruption mainly on areas in xterm redrawn
(but not those that get scrolled up) immediately after launching the testcase.

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