* Cells loaded from walk-data are half-transparent.
* The player symbol is half-transparent when showing different floors.
* Clear the texture before drawing a small map so that no garbage is
left when the drawing is clipped.
Major differences from DrawDungeon.hll are:
- DGN, DTX, TES are loaded from individual files, not from a DLF archive
- 2D map functions are not used
- (unimplemented) Spinning motion of event markers
- (unimplemented) Additional 3D object types (polygon models and roofs)