I am interested in the actual source code. Could you send me a copy?
The implementation I’m working with never fills rows where y==ymax, since thosse edges get removed from the active list before filling. so horizontal upper edges never get filled. But modifying the logic to only remove edges when y==ymax+1 messes up the next row, since then there are extra intersections on the scanline, and filling between edge pairs doesn’t work properly anymore.