Usually with analytic AA you just use Porter-Duff blending, because rendering all the objects simultaneously doesn't buy you much except for performance (which

Usually with analytic AA you just use Porter-Duff blending, because rendering all the objects simultaneously doesn't buy you much except for performance (which is why piet-metal does it that way). For supersampling AA you can render all the objects at once, like Flash did, and this does improve rendering quality around coincident edges. Oddly (in my opinion), some rasterizers such as Skia's use supersampling for individual paths and Porter-Duff blending when overlaying different paths on top of one another. This means that you don't have seams between subpaths of the same path, but different paths can have seams on coincident edges. I don't like this tradeoff personally, because it has a lot of the downsides of analytic AA without the benefit of antialiasing quality, but for better or worse this approach is widely used.