[help] Texture mapping

Optimally, yes, you'll break rendering into groups of polys that share the same texture, or textures. In reality, as long as you're using less textures and available texture stages, you could get away with blending the other textures in with a weight of 0. Our heightmap system uses 4 textures, and requires hardware with 4 available textures, so we just choose a percentage of each texture encoded as color on each vertex. It works. It's cheap and easy to code. I'm pretty sure we could get better performance if we actually split up the map instead of using 4 large, tri-linear filtered textures (well, 5 actually, a first pass does just lightmap and fill in Z) over everything.