Finding outline of connected rectangles

totebo

To get a seamless texture behind a Box2D world I need to find the outline of a number of arbitrarily placed rectangles. Tricky! Please see illustration below. After a lot of tinkering and Googling this problem is beating me. Any math geniuses out there who could help?

totebo

I've now managed to get all the points of the outline, but they're in random order. Next step would be to order them in clockwise order to draw the shape. Still listening for other solutions!

SinisterSoft

With that kind of complex shape, it might be faster for box2d to process collision with them as the 4 boxes rather than the new shape?

antix

Will their edges overlap at any stage or will they just touch edges?

totebo

@sinistersoft: The boxes are individual objects in Box2D already, I'm just looking to fill the "cookie cutter" holes (actually a road) with a background that tiles nicely.

@antix: The edges should never overlap, but I find that the conversion from Rube sometimes isn't as exact as I'd like, so there are small overlaps sometimes.

In other news, I miraculously managed to find Lua code to sort the points clockwise. Initial tests appear to indicate it works! Code here: http://stackoverflow.com/Questions/6989100/sort-points-in-clockwise-order

totebo

Short lived happiness: The sorting doesn't seem to handle concave cases. Time for bed.

totebo

Wow. I got it to work, but it makes no sense. I fill each individual rectangle with a shape with a tiled pattern. For some reason it tiles perfectly, even though the rectangles (and therefore shapes) are in arbitrary places. I shall accept this magic and move on.

antix

@totebo, dang

Generally most systems breakdown concave shapes into multiple convex ones for processing (or so it seems).

antix

Wow. I got it to work, but it makes no sense. I fill each individual rectangle with a shape with a tiled pattern. For some reason it tiles perfectly, even though the rectangles (and therefore shapes) are in arbitrary places. I shall accept this magic and move on.

Thats how shapes work. If you set your tiling pattern it automatically does that

totebo

Incredible. I'll stop this rebuilding the wheel nonsense, then.