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69 lines
1.9 KiB
Plaintext
69 lines
1.9 KiB
Plaintext
Heightmap module
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by Marc Lepage
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OVERVIEW
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The heightmap module uses the diamond-square algorithm to generate cloud or
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plasma fractal heightmaps which can be used for terrain.
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USAGE
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-- import module
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require "heightmap"
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-- create 32x32 heightmap
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map = heightmap.create(32, 32)
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-- examine each height value
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for x = 0, map.w do
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for y = 0, map.h do
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print(map[x][y])
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end
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end
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-- define a custom height function (reusing the default but scaling it)
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function f(map, x, y, d, h)
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return 2 * heightmap.defaultf(map, x, y, d, h)
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end
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-- use it to create a larger non-square heightmap
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map = heightmap.create(100, 200, f)
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HOW IT WORKS
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The heightmap must be a square the size of a power of two, plus one, so that
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it can be evenly divided. For example, 4x4 cells will require 5x5 vertices.
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If another size is specified, a sufficiently large power of two square will
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be used, and the result clipped to the desired size.
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First the four corners are seeded with a random value (C).
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Then each square is used to set the value of its center (S) based on the
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average of its four corners (plus some randomness).
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Then each diamond is used to set the value of its center (D) based on the
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average of its four points (plus some randomness).
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The square and diamond steps continue until all values have been set:
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4 S 2 D 2 S 1 D 1
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C...C c...c c.D.c c.d.c cDdDc
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..... ..... ..... .S.S. DsDsD
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..... ..S.. D.s.D d.s.d dDsDd
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..... ..... ..... .S.S. DsDsD
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C...C c...c c.D.c c.d.c cDdDc
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The default height function randomly displaces values by up to +/- 0.5 of the
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step size. So above, the corners will be from -2 to +2, the center will be
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the mean of the corners randomly displaced from -1 to +1, and so on.
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RESOURCES
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http://en.wikipedia.org/wiki/Diamond-square_algorithm
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http://en.wikipedia.org/wiki/Heightmap
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http://en.wikipedia.org/wiki/Fractal_landscape
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