- Rendering: two pass: 1st pass renders the scaled down background (possibly not
  rendering floor, can be just pure green for "grass") to prevent overflows,
  second pass renders the tracks (or the nearest part of it).
- Track format: just a list of (x,y,z,transform,block_type) elements.
- Start and finish blocks will be just the first/last checkpoint blocks (no need
  for special start, finish and CP).