kicad/pcbnew/autorouter/rect_placement/RectanglePlacement.txt

A class that fits subrectangles into a power-of-2 rectangle

(C) Copyright 2000-2002 by Javier Arevalo
This code is free to use and modify for all purposes

You have a bunch of rectangular pieces. You need to arrange them in a
rectangular surface so that they don't overlap, keeping the total area of the
rectangle as small as possible. This is fairly common when arranging characters
in a bitmapped font, lightmaps for a 3D engine, and I guess other situations as
well.

The idea of this algorithm is that, as we add rectangles, we can pre-select
"interesting" places where we can try to add the next rectangles. For optimal
results, the rectangles should be added in order. I initially tried using area
as a sorting criteria, but it didn't work well with very tall or very flat
rectangles. I then tried using the longest dimension as a selector, and it
worked much better. So much for intuition...

These "interesting" places are just to the right and just below the currently
added rectangle. The first rectangle, obviously, goes at the top left, the next
one would go either to the right or below this one, and so on. It is a weird way
to do it, but it seems to work very nicely.

The way we search here is fairly brute-force, the fact being that for most off-
line purposes the performance seems more than adequate. I have generated a
japanese font with around 8500 characters and all the time was spent generating
the bitmaps.

Also, for all we care, we could grow the parent rectangle in a different way
than power of two. It just happens that power of 2 is very convenient for
graphics hardware textures.

I'd be interested in hearing of other approaches to this problem. Make sure
to post them on http://www.flipcode.com

See also
http://www.flipcode.com/archives/Rectangle_Placement.shtml
http://kossovsky.net/index.php/2009/07/cshar-rectangle-packing