On Mon, Jul 16, 2012 at 08:43:17PM -0700, Paul Berry wrote: > Also, I'm not convinced that #3 is necessary. Is there something in the > spec that dictates this behaviour? My reading of the spec is that if the > vertex shader writes to gl_BackColor but not glFrontColor, then the > contents of gl_Color in the fragment shader is undefined. Oh, I remember why I did that in the first place. All the front/back piglit tests only write the appropriate color slot and not the other one. The language is annoying: The following built-in vertex output variables are available, but deprecated. A particular one should be written to if any functionality in a corresponding fragment shader or fixed pipeline uses it or state derived from it. Otherwise, behavior is undefined. out vec4 gl_FrontColor; out vec4 gl_BackColor; out vec4 gl_FrontSecondaryColor; out vec4 gl_BackSecondaryColor; [...] One could argue that you don't "use" gl_FrontColor if all your polygons are back-facing. Dunno. Do you consider all of the twoside piglit tests buggy? We can fix *that*. OG.
