On Tuesday 08 February 2005 16:43, Timothy Miller wrote: > On Tue, 8 Feb 2005 16:06:05 -0500, Daniel Phillips wrote: > > Vertical rasterization: > > > > - one multiply per interpolant to correct for pixel alignment > > Well, here's what I think may have to happen (and it's going to kinda > suck): Since there's an alignment correction for each interpolant, > plus we have to do the vertical interpolation, I suggest we use 2 or > maybe up to 4 multpliers and have the vertical logic iterate over the > interpolants. For 17 interpolants and 3 multipliers, that's 6 cycles > to compute all interpolants so that the horizontal units can work on > them. But that's only 3 fp adders and 3 fp multipliers (gotta design > one of those!).
So the texture pipe will stall for every span less than 12 pixels wide, which will be easily noticeable I think. If we get rid of one interpolant we get back two multipliers and can do the job in 4 cycles, with one multiplier left over. Saving 1/3 of the span setup in return for losing 1/17th of the interpolants sounds like a pretty good deal to me :-) Supposing that we can manage 3 million triangles/second, that is 100,000 per frame at 30 FPS. Assuming an overdraw factor of 3 and screen size of 1280x1024, that is about 39 pixels/triangle. So most triangles are going to spend a lot of time stalling if the span setup is too slow. Of course, 3 million triangles/second might be just too ambitious. > > With 17 interpolants, most of which need perspective correction (in > > my opinion; some may think this justifiable only for textures) > > we've already exceeded our multiplier budget and haven't even begun > > to think about filtering, blending, mipmapping, fog and probably > > other things. > > That's 17 multiplies, but we can do some looping if we have to. 17 for vertical and 34 for horizontal, isn't it? 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)
