heightmap/heightmap.lua
2011-10-22 22:46:16 -04:00

107 lines
3.2 KiB
Lua

-- Heightmap module
-- Copyright (C) 2011 Marc Lepage
local max, random = math.max, math.random
module(...)
-- Find power of two sufficient for size
local function pot(size)
local pot = 2
while true do
if size <= pot then return pot end
pot = 2*pot
end
end
-- Create a table with 0 to n zero values
local function tcreate(n)
local t = {}
for i = 0, n do t[i] = 0 end
return t
end
-- Square step
-- Sets map[x][y] from square of radius d using height function f
local function square(map, x, y, d, f)
local sum, num = 0, 0
if 0 <= x-d then
if 0 <= y-d then sum, num = sum + map[x-d][y-d], num + 1 end
if y+d <= map.h then sum, num = sum + map[x-d][y+d], num + 1 end
end
if x+d <= map.w then
if 0 <= y-d then sum, num = sum + map[x+d][y-d], num + 1 end
if y+d <= map.h then sum, num = sum + map[x+d][y+d], num + 1 end
end
map[x][y] = f(map, x, y, d, sum/num)
end
-- Diamond step
-- Sets map[x][y] from diamond of radius d using height function f
local function diamond(map, x, y, d, f)
local sum, num = 0, 0
if 0 <= x-d then sum, num = sum + map[x-d][y], num + 1 end
if x+d <= map.w then sum, num = sum + map[x+d][y], num + 1 end
if 0 <= y-d then sum, num = sum + map[x][y-d], num + 1 end
if y+d <= map.h then sum, num = sum + map[x][y+d], num + 1 end
map[x][y] = f(map, x, y, d, sum/num)
end
-- Diamond square algorithm generates cloud/plasma fractal heightmap
-- http://en.wikipedia.org/wiki/Diamond-square_algorithm
-- Size must be power of two
-- Height function f must look like f(map, x, y, d, h) and return h'
local function diamondsquare(size, f)
-- create map
local map = { w = size, h = size }
for c = 0, size do map[c] = tcreate(size) end
-- seed four corners
local d = size
map[0][0] = f(map, 0, 0, d, 0)
map[0][d] = f(map, 0, d, d, 0)
map[d][0] = f(map, d, 0, d, 0)
map[d][d] = f(map, d, d, d, 0)
d = d/2
-- perform square and diamond steps
while 1 <= d do
for x = d, map.w-1, 2*d do
for y = d, map.h-1, 2*d do
square(map, x, y, d, f)
end
end
for x = d, map.w-1, 2*d do
for y = 0, map.h, 2*d do
diamond(map, x, y, d, f)
end
end
for x = 0, map.w, 2*d do
for y = d, map.h-1, 2*d do
diamond(map, x, y, d, f)
end
end
d = d/2
end
return map
end
-- Default height function
-- d is depth (from size to 1 by powers of two)
-- h is mean height at map[x][y] (from square/diamond of radius d)
-- returns h' which is used to set map[x][y]
function defaultf(map, x, y, d, h)
return h + (random()-0.5)*d
end
-- Create a heightmap using the specified height function (or default)
-- map[x][y] where x from 0 to map.w and y from 0 to map.h
function create(width, height, f)
f = f and f or defaultf
-- make heightmap
local map = diamondsquare(pot(max(width, height)), f)
-- clip heightmap to desired size
for x = 0, map.w do for y = height+1, map.h do map[x][y] = nil end end
for x = width+1, map.w do map[x] = nil end
map.w, map.h = width, height
return map
end