Initial commit.

README

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+Heightmap module
+by Marc Lepage
+
+
+OVERVIEW
+
+The heightmap module uses the diamond-square algorithm to generate cloud or
+plasma fractal heightmaps which can be used for terrain.
+
+
+USAGE
+
+-- import module
+require "heightmap"
+
+-- create 256x256 heightmap
+map = heightmap.create(256, 256)
+
+-- examine each height value
+for x = 0, map.w do
+    for y = 0, map.y do
+        print(map[x][y])
+    end
+end
+
+-- define a custom height function (reusing the default but scaling it)
+function f(map, x, y, d, h)
+    return 2 * heightmap.defaultf(map, x, y, d, h)
+end
+
+-- use it to create a new heightmap
+map = heightmap.create(256, 256, f)
+
+
+HOW IT WORKS
+
+The heightmap must be a square the size of a power of two, plus one, so that
+it can be evenly divided. For example, 4x4 cells will require 5x5 vertices.
+
+First the four corners are seeded with a random value (C).
+
+Then each square is used to set the value of its center (S) based on the
+average of its four corners (plus some randomness).
+
+Then each diamond is used to set the value of its center (D) based on the
+average of its four points (plus some randomness).
+
+The square and diamond steps continue until all values have been set:
+
+      4     S 2    D 2    S 1    D 1
+    C...C  c...c  c.D.c  c.d.c  cDdDc
+    .....  .....  .....  .S.S.  DsDsD
+    .....  ..S..  D.s.D  d.S.d  dDsDd
+    .....  .....  .....  .S.S.  DsDsD
+    C...C  c...c  c.D.c  c.d.c  cDdDc
+
+The default height function randomly displaces values by up to +/- 0.5 of the
+step size. So above, the corners will be from -2 to +2, the center will be
+the mean of the corners randomly displaced from -1 to +1, and so on.
+
+
+RESOURCES
+
+http://en.wikipedia.org/wiki/Diamond-square_algorithm
+http://en.wikipedia.org/wiki/Heightmap
+http://en.wikipedia.org/wiki/Fractal_landscape