On Tue, 15 Feb 2005 21:02:13 -0500, Daniel Phillips <[EMAIL PROTECTED]> wrote: > On Tuesday 15 February 2005 18:44, Lourens Veen wrote: > > On Tuesday 15 February 2005 23:47, I wrote: > > > At this point I'm fretting more about DDA precision than the > > > perspective divide. I seriously doubt we'll get stable results > > > stepping across the whole screen with 16 bit precision. I'm > > > mulling over a couple of suggestions, short of adding more bits. > > > > ...At any rate, could we assume a maximum of 2048x1536 for the > > resolution? That means 11 bits for integer screen coordinates, so > > we'd have an 11.5 split if we did fixed point (and floating point > > just doesn't make sense to me here really, comments?). > > Floating point makes a whole lot of sense here because we don't have > much control over the input parameters, which can vary over wide > ranges. The W divide introduces a further, large degree of variation > for new and far objects. A typical nasty case is a viewpoint near a > huge vertical plane running far into the distance, i.e., looking along > the side of a building.
Without anisotropic filtering, you're never going to get good results out of this anyhow. > > > That means > > that if the span is larger than 32 pixels, we get in trouble. In > > fact, we'd need 11.11 probably to get it perfectly right. Which means > > 22 bits adders :-(. > > You can get in trouble way before hitting a full pixel error in the > geometry. For example, the jaggies may start doing wild things in > animation instead of crawling along the edges nicely like they are > supposed to. > An 11.11 adder isn't as bad as an 18-bit float adder. Not even close. :) > > > Just some thoughts. > > Three options that seem viable to me are: > > 1) Correct each interpolant on the fly using a single multiplier in a > round robin. > > 2) Chop up big geometry in the driver vertically and horizontally into > bite size chunks. > > 3) More bits, just for the interpolants. > > The second of these seems the most pragmatic since it can be offloaded > to the host, saving gates and Timothy cycles. The extra work would > level out nicely because larger triangles incur most of the penalty, > and there should be fewer of them. For best visual stability, the > clipping planes would form a rectangular mesh in screen space. Note > that this means small triangles do not necessarily escape intact, > however they are more likely to. I like this option too. :) _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
