By VDP background layers, I mean things like the VF2 stage floors or Last Bronx's backgrounds: Many saturn games used skewed background layers for floors to save polygons. Sonic R, for example, does this. So that brings me to Sonic Jam World, one of the best examples of a 3D engine on the saturn -- how does it perform so well? My first thought would be that the floor is a VDP background layer, and thus it's sparse on polygons. But there is one part in particular that trips me up the river: I'm curious how this was achieved. Is it just a perspective projection of a polygon object that is composited over the VDP background layer, or is what I think is a VDP background layer actually a polygon mesh, and this is actual lower geometry? Any ideas?
The floor itself (and the sky) are rendered on the VDP RGB0 layer, while the waterfall/landscapes/3D "Polygon" (and I use quotes there wisely) are sprites: And the "Polygon" (sprites) rendering the waterfalls/mounts over the floor:
