Keith Whitwell pisze: > On Mon, 2009-11-23 at 17:28 -0800, Brian Paul wrote: > >> For OpenGL, the front-facing attribute is either 0 (back) or 1 (front) >> rather than +/-1. >> >> I think we'll need to do some additional work (insert a MAD instr?) in the >> Mesa->TGSI translation to account for this difference. I could dig into >> that someday... >> > > I'm assuming DX or some other API uses +/-1? > > If we define tgsi to use +/-1, then the GL 0/1 version can be reached by > just saturating. Getting from 0/1 to +/-1 looks like it would be a MAD > as you say. Probably +/-1 is easy to calculate as the sign of the > determinant, which would be an intermediate step to calculate GL's > version. > > If it's OK, let's define TGSI's face reg as +/-1, and have Mesa insert > the saturate if necessary. > > OK, I have documented that as negative/positive since it gives us more freedom in the future. If it is a problem, we can explicitly say it's either -1 or +1 later.
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