Yeah. On the GC, games can reset some "bounding box" registers, draw some 3d geometry, and then read out the 2D coordinates of the bounding box of the things dr

Yeah. On the GC, games can reset some "bounding box" registers, draw some 3d geometry, and then read out the 2D coordinates of the bounding box of the things drawn. Games like Paper Mario uses it to make a copy of that region and apply various effects to it, and if the region is wrong weird things happen. There are no such bounding box registers on PC GPUs, so you have to either software transform the coordinates and ignore that your results won't be perfect (some pixels might have been thrown away due to z tests etc and wouldn't be counted in the bbox), or you use some modern shader tricks to simulate it in hardware, which is what the current Dolphin authors have now implemented.