On Tuesday 01 February 2005 13:55, Timothy Miller wrote: > Correct me if I'm wrong, but "normalized device coordinates" have > been projected but not scaled, right?
Rotated and projected so that all view planes are orthogonal, and scaled to [-1, +1] in all dimensions I think. > >>Therein lies a problem. Since the reciprocal isn't precise (we use > >>only 10 mantissa bits when computing it) > > > > Hmm, I thought we had 18 bits of precision readily available. Is > > this a consequence of using linear interpolation for the divide? > > It's a consequence of using a lookup table with only 10 address bits > for the reciprocal. But the linear interpolation then adds some more bits, I thought. > > My guess is that in a perfect world we should round down, but > > saving a few gates is enough excuse for rounding up. Fortunately > > it's a FPGA, so there's hardly any penalty for guessing wrong the > > first time. > > Your GUESS? Is there anything which states it definitively? I'm waiting for an OpenGL lawyer out there to speak up. I know they're lurking ;-) > Another thing that I'm going to change is that the X values are going > to be fixed-point. It won't hurt anything (on the contrary!), and > it'll make the logic lots simpler. Additionally, it makes it easier > to round 0.5 down. It's still more logic but not horribly bad. That is for sure the right thing to do. Y should be fixed point too, IMHO. Regards, Daniel _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
