Terrain TODO
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o shadows
o allow multi-resolution textures (4x normals)
o collision detection
o object placement
o fix-up between detail levels
o edge handling (clean border, wrapping/spherical mapping, etc)
o texture blending
o higher resolution normals
o convert MOLA data to tiles
o procedural generation
o port atmospheric scattering shader to new planet object

✔ load deepzoom images from xml files directly
✔ upsample tiles when loading new ones
✔ fix tile alignment
✔ support for moving area-of-focus
✔ area-of-focus follows camera
✔ hide higher-detail rings when zoomed out
✔ support for 16-bit heightmaps (MOLA/BMNG)
✔ convert BMNG data to tiles


space.meshes.terrain:
  - type: (simple|deepzoom)
  - mapping: (flat|sphere)
  - rings

  - setPosition(pos)
  - setLevel(level)
  - addRing(level)

space.meshes.terrain_ring:
  - level
  - centertile
  - centeroffset
  - textures

  - createTile(offset)


space.meshes.terrain_tile:
  - material

  - setTextures(textures)