- front and back labels where inverted:
+z is the front of the cube and -z is its back
when looking at the cube from the outside
with a camera pointing towards -z (and the cube
in front of it). This is the GL definition.
- make the synthetic uvXXX debug environment
colors match those of the debug environment
(except for -Z/back which is magenta instead
of black).
- add some documentation about skybox and cube map.