The jumpy polygons are because the PSX's GPU only accepts vertex positions in screen coordinates, meaning that vertices always snap to hard integer values. Ther

The jumpy polygons are because the PSX's GPU only accepts vertex positions in screen coordinates, meaning that vertices always snap to hard integer values. There is no sub-pixel accuracy. That's not a limitation caused by the PSX's lack of an FPU though. A large part of the render pipeline and standard libraries are built around the use of fixed point math, i.e. using integers to simulate decimal values. The GTE co-processor which handles 3D math makes use of standardized fixed-point types. So the PSX would have been capable of calculating sub-pixel coordinate values, it's just that the communication between CPU and GPU was designed to use only integer screen coordinate values.