- speedup sprite display by a factor of 4 - 7 by keeping them partially sorted
Note:
- sprite shadow draw is even more improved
- the n^2 dependency is substituted by a worst case n^(3/2) algorithm
- wolf among 186 sheep is playable on a 2.6 GHz Pentium with 25 - 60 fps
(we started with 1 - 2 fps)
- this patch is not yet cleaned up - the sprites are drawn in a unstable order,
jumping marbles may switch from frame to frame in stack sequence
