https://bugs.freedesktop.org/show_bug.cgi?id=87407
Bug ID: 87407
Summary: glReadPixels not working when the RGBA component is of
the type dFdy(abs())
Product: Mesa
Version: unspecified
Hardware: Other
OS: All
Status: NEW
Severity: normal
Priority: medium
Component: Mesa core
Assignee: mesa-dev@lists.freedesktop.org
Reporter: ago...@igalia.com
Created attachment 110945
--> https://bugs.freedesktop.org/attachment.cgi?id=110945&action=edit
Patch to correct the GCC warnings and introduce the 2 latest use cases
At bug 82991 we extended the piglit test glsl-deriv-varyings with 3 new cases:
http://lists.freedesktop.org/archives/piglit/2014-December/013648.html
However, a couple of GCC warnings were introduced in piglit and the last 2
extended cases using dFdx(abs()) and dFdy(abs()) were not being tested.
After fixing the warnings (see attached patch) and getting the 2 last cases to
work, a new bug has been identified in mesa.
For example, in this piglit test, using the following fragment shader:
uniform sampler2D tex2d;
varying vec2 texCoords;
void main()
{
gl_FragColor = vec4(dFdx(abs(texCoords.x)) * 40.0,
dFdy(abs(texCoords.y)) * 40.0,
0.0, 1.0);
}
The piglit result is:
Probe color at
Expected: 0.800000 0.400000 0.000000
Observed: 0.800000 0.000000 0.000000
PIGLIT: {"result": "fail" }
However, running manually the test with:
$ PIGLIT_SOURCE_DIR="<path_to>/piglit.git" PIGLIT_PLATFORM="mixed_glx_egl"
<path_to>/piglit.git/bin/glsl-deriv-varyings
We can see that the pixels painted in the display are, actually, the expected
ones.
Hence, the problem happens when checking the colors of the pixels through
glReadPixels.
I've also checked that the problem is reproducible, at least, with swrast, i965
(gen6) and nouveau.
While I'm investigating this problem, I've sent a patch proposal to remove
these test cases and fix also the introduced warnings at:
http://lists.freedesktop.org/archives/piglit/2014-December/013764.html
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