<html> <head> <base href="https://bugs.freedesktop.org/" /> </head> <body> <div> <a class="bz_bug_link bz_status_NEW " title="NEW --- - [llvmpipe] piglit glsl-fs-frontfacing regression" href="https://bugs.freedesktop.org/show_bug.cgi?id=67692#c1">Comment # 1</a> on <a class="bz_bug_link bz_status_NEW " title="NEW --- - [llvmpipe] piglit glsl-fs-frontfacing regression" href="https://bugs.freedesktop.org/show_bug.cgi?id=67692">bug 67692</a> from <a class="email" href="mailto:sroland@vmware.com" title="Roland Scheidegger <sroland@vmware.com>"> Roland Scheidegger</a> <pre>Looks like the gallium docs and the "old" tgsi_semantic_face value don't quite agree with what glsl actually wants: The shader does this: void main() { gl_FragColor = vec4(0.0, float(gl_FrontFacing), 1.0 - float(gl_FrontFacing), 0.0); } And it gets translated to: FRAG PROPERTY FS_COLOR0_WRITES_ALL_CBUFS 1 DCL IN[0], FACE, CONSTANT DCL OUT[0], COLOR DCL TEMP[0] DCL TEMP[1..2], LOCAL IMM[0] FLT32 { 0.0000, 1.0000, 0.0000, 0.0000} 0: MOV_SAT TEMP[0], IN[0] 1: MOV TEMP[1].xw, IMM[0].xxxx 2: AND TEMP[2].x, TEMP[0].xxxx, IMM[0].yyyy 3: MOV TEMP[1].y, TEMP[2].xxxx 4: AND TEMP[2].x, TEMP[0].xxxx, IMM[0].yyyy 5: ADD TEMP[2].x, IMM[0].yyyy, -TEMP[2].xxxx 6: MOV TEMP[1].z, TEMP[2].xxxx 7: MOV OUT[0], TEMP[1] 8: END OUT[0].x = 0.000000 OUT[0].w = 0.000000 That is pretty strange but it looks like it would work (thanks to the mov_sat) if - backside value is 0.0 or smaller - frontside value is 1.0 or larger Might be best to go back and just generate 1.0 for front again to avoid trouble - -1.0 instead of 0.0 for back should be just fine. glsl translation is really relying on undocumented behavior here though, and the lax definition in gallium (saying it must be positive or negative) was intentional (matching old specs). Not sure though if things would work as well if that face would be used differently (i.e. as a bool/int).</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the assignee for the bug.</li> </ul> </body> </html>