On Wednesday 09 February 2005 07:30, Lourens Veen wrote: > On Wednesday 09 February 2005 02:24, Daniel Phillips wrote: > > 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 :-) > > However, the smaller the triangles the less accurate perspective > correction we need. Essentially, the T&L engine in software will take > care of it by moving the vertices appropriately. Quake 1 did one > reciprocal every 16 pixels. > > Maybe we could figure out some way of decreasing perspective > correction quality in exchange for performance as triangles get > smaller?
It sounds like a good idea, but a little messy. Perhaps it's a good candidate for an update. After all, updating is one of the really cool things about the fpga approach. 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)
