What I don't understand - why is there this "cover table" with precomputed per-cell-row coverage? I.e. why is the cover table computed per-cell-row when the segments are specialized per-cell? There is the paper "ravg.pdf" that gets by with basically one "cover" integer per tile, plus some artificial fixup segments that I believe are needed even in the presence of such a cover table. I'm probably missing something, someone who is deeper in the topic please enlighten me?