[Gzz] 17th-20th (jvk)

[Janne Kujala]

17th-20th: irregular shape work

Thought about implementing irregular shapes using standard
OpenGL 1.1 with or without the dot3 texenv extension.

Constant edge width on different scales can be achieved by 
computing each mipmap level separately with the proper width 
for the scale. This should interpolate perfectly because 
the texture stores displacement values.

Problems:
- Projective color interpolation and dot3 input mapping 
  limitations force the displacement texture values to be
  between 0.75 and 1. Is 64 levels enough?

- Distortion amplitude/period ratio must be constant for
  the edge line to have the proper pre-computed width. 
  The corners of a piece cannot simply be interpolated to 
  zero amplitude for switching in/out displacement direction.

- Outer edge displacement values do not interpolate very
  well between the pre-computed angles when there is a big 
  displacement gradient nearby ( d width / d angle is large
  when angle is normal to the big gradient ).

        jvk