https://bugs.freedesktop.org/show_bug.cgi?id=30152
--- Comment #7 from Fredrik Höglund fredrik@kde.org 2010-09-27 18:04:07 PDT --- I've pushed another piglit test that uses 7 varyings to:
http://cgit.freedesktop.org/~fredrik/piglit
While I was looking at the code for the vertex shader I also realized that it was setting gl_TexCoord[0] even though the fragment shader wasn't using it. I've fixed that in kwin and updated the code in the original piglit test to reflect that change.
The number of varyings used is always an odd number, so even with gl_texCoord[0] being set the available outputs shouldn't have been exceeded though.