Comment by dahart

> What type of filter do you mean? […] the approach described doesn’t go into the details of how coverage is computed

This article does clip against a square pixel’s edges, and sums the area of what’s inside without weighting, which is equivalent to a box filter. (A box filter is also what you get if you super-sample the pixel with an infinite number of samples and then use the average value of all the samples.) The problem is that there are cases where this approach can result in visible aliasing, even though it’s an analytic method.

When you want high quality anti-aliasing, you need to model pixels as soft leaky overlapping blobs, not little squares. Instead of clipping at the pixel edges, you need to clip further away, and weight the middle of the region more than the outer edges. There’s no analytic method and no perfect filter, there are just tradeoffs that you have to balance. Often people use filters like Triangle, Lanczos, Mitchell, Gaussian, etc.. These all provide better anti-aliasing properties than clipping against a square.