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For an analytic derivation of antialiasing for lines or polygons
given radially-symmetric point-spread function (PSF), look at:

	Anti-Aliasing through the use of Coordinate Transformations
	Turkowski, Kenneth
	ACM Transactions on Graphics
	Vol. 1, No. 3, July 1982, pp. 214-234

This outlines the transformation of the radially symmetric point-spread
function into another function which is the result of convolving the
line or polygon edge with the PSF.  One simply calculates the distance
of a pixel center from the edge, and uses that as an index into a table
which contains the proper value to put into the frame store.

The distance of successive pixels near an edge can be computed incrementally
through a linear coordinate transformation:
	du = a dx + b dy
where (b, -a) is a unit vector pointing from one vertex to the other.
If dx is 0, then a unit change in y (dy=1) produces a change in distance
of a (du=a).  This is just a normalized Bresenham algorithm.
-- 
Ken Turkowski @ Apple Computer, Cupertino, CA
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