[pygame] Dirty rect overlapping optimizations

[René Dudfield <renesd@xxxxxxxxx>]

Because rectangles can overlap, it's possible to reduce the amount drawing done when using them for dirty rect updating. If there's two rectangles overlapping, then we don't need to over draw the overlapping area twice. Normally the dirty rect update algorithm used just makes a bigger rectangle which contains two of the smaller rectangles. But that's not optimal.

But, as with all over draw algorithms, can it be done fast enough to be worth it?

Here's an article on the topic:
    http://gandraxa.com/detect_overlapping_subrectangles.xml

jmm0 made some code here:
    https://bitbucket.org/jmm0/optimize_dirty_rects/src/c2affd5450b57fc142c919de10e530e367306222/optimize_dirty_rects.py?at=default&fileviewer=file-view-default

DR0ID, also did some with tests and faster code...
https://bitbucket.org/dr0id/pyweek-games/src/1a9943ebadc6e2102db0457d17ca3e6025f6ca60/pyweek19-2014-10/practice/dirtyrects/?at=default


So far DR0ID says it's not really fast enough to be worth it. However, there are opportunities to improve it. Perhaps a more optimal algorithm, or one which uses C or Cython.

"worst case szenario with 2000 rects it takes ~0.31299996376 seconds"
If it's 20x faster in C, then that gets down to 0.016666. Still too slow perhaps.

It's not an embarrassingly parallel problem... I think. But I haven't thought on it much at all. Maybe there is a use for multi core here.

Anyone done any other work like this? Or know of some good algos for this?

cheers,