[r7]
- abstract texture mapping.
.
[r7]
.
.
[r7]
- prepare to add my own texture mapping algorithm.
[r7]
- clean up.
[r7]
- temp.
[r7]
- support rendering 'white' triangle.
.
.
[r7]
.
[r7]
- fix wrong 'ensure_min_max' bug.
- update implementation.