I did a little more experimentation. If you have an antialiased line on integer coordinates that's exactly 45 degrees, the center line is alpha 1.0. Depending on how you interpret "coverage", this is slightly off, because the pixel corners lie slightly outside of the line, so you don't have 100% coverage. I'm not sure if I've done the math right, but it looks like in that case, the pixel should have 83% coverage. However, as the line tends toward vertical or horizontal, the given antialias algorithm tends toward expected results, as far as I can judge.
Also, coverage isn't the only way to compute antialiasing, although I'm not sure how much leeway the OpenGL spec gives. If that's really a problem, we can compute an attenuation factor based on slope. But I don't think it'll be a problem. _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
