lukcho

GLSL compiler bug

Discussion created by lukcho on Nov 17, 2011
Latest reply on Mar 4, 2012 by pillum

 

I dont know if this is the right forum for bug reports, but i could not find better one. Anyway here is the bug i found:

this fragment shader

#version 330
out vec4 color0;
void main() {
     const float a = 1;
     float b = clamp(a, 0, 1);
     color0 = vec4(b);
}

outputs vec4(0,0,0,0) instead of vec4(1,1,1,1).

if either the const qualifier for "a" or the clamp operation is removed, the shader will work correctly.

neither the shader version nor the shader type are important - happens with all versions and all shader types

 

Edit:

also tested it with the GPU Shader Analyser tool (very nice tool by the way) and it shows this assembly code:

; -------- Disassembly --------------------
00 ALU: ADDR(32) CNT(1)
0 x: MOV R0.x, 0.0f
01 EXP_DONE: PIX0, R0.xxxx
END_OF_PROGRAM

appears to be a bug with the compiler const-folding

 



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