From ccc1d936df191bb43465e3828362f31f8d387b26 Mon Sep 17 00:00:00 2001
From: Alexander Gavrilov <angavrilov@gmail.com>
Date: Wed, 2 Oct 2013 20:00:03 +0400
Subject: [PATCH] Add a Perlin noise test script.

---
 scripts/devel/test-perlin.lua | 132 ++++++++++++++++++++++++++++++++++
 1 file changed, 132 insertions(+)
 create mode 100644 scripts/devel/test-perlin.lua

diff --git a/scripts/devel/test-perlin.lua b/scripts/devel/test-perlin.lua
new file mode 100644
index 000000000..a6642e125
--- /dev/null
+++ b/scripts/devel/test-perlin.lua
@@ -0,0 +1,132 @@
+-- Generates an image using multiple octaves of perlin noise.
+
+local args = {...}
+local rng = dfhack.random.new(3)
+
+if #args < 3 then
+    qerror('Usage: devel/test-perlin <fname.pgm> <density> <coeff|expr...x[...y[...z]]>...')
+end
+
+local fname = table.remove(args,1)
+local goal = tonumber(table.remove(args,1)) or qerror('Invalid density')
+
+local zscale = 6
+
+local coeffs = {}
+local fns = {}
+
+local env = copyall(math)
+env.apow = function(x,y) return math.pow(math.abs(x),y) end
+
+for i = 1,#args do
+    local fn = rng:perlin(3);
+    local fn2 = rng:perlin(3);
+    local fn3 = rng:perlin(3);
+    local fn4 = rng:perlin(3);
+
+    fns[i] = fn;
+
+    local val = string.match(args[i],'^([+-]?[%d.]+)$')
+    if val then
+        coeffs[i] = function(x) return x * val end
+    else
+        local argstr = 'x'
+        if string.match(args[i], '%f[%w]w%f[^%w]') then
+            argstr = 'x,y,z,w'
+            fns[i] = function(x,y,z)
+                return fn(x,y,z), fn2(x,y,z), fn3(x+0.5,y+0.5,z+0.5), fn4(x+0.5,y+0.5,z+0.5)
+            end
+        elseif string.match(args[i], '%f[%w]z%f[^%w]') then
+            argstr = 'x,y,z'
+            fns[i] = function(x,y,z)
+                return fn(x,y,z), fn2(x,y,z), fn3(x+0.5,y+0.5,z+0.5)
+            end
+        elseif string.match(args[i], '%f[%w]y%f[^%w]') then
+            argstr = 'x,y'
+            fns[i] = function(x,y,z)
+                return fn(x,y,z), fn2(x,y,z)
+            end
+        end
+
+        local f,err = load(
+            'return function('..argstr..') return ('..args[i]..') end',
+            '=(expr)', 't', env
+        )
+        if not f then
+            qerror(err)
+        end
+        coeffs[i] = f()
+    end
+end
+
+function render(thresh,file)
+    local area = 0
+    local line, arr = '', {}
+
+    for zy = 0,1 do
+        for y = 0,48*4-1 do
+            line = ''
+            for zx = 0,1 do
+                for x = 0,48*4-1 do
+                    local tx = (0.5+x)/(48*2)
+                    local ty = (0.5+y)/(48*2)
+                    local tz = 0.5+(zx+zy*2)/(48*2/zscale)
+                    local v1 = 0
+                    for i = 1,#coeffs do
+                        v1 = v1 + coeffs[i](fns[i](tx,ty,tz))
+                        tx = tx*2
+                        ty = ty*2
+                        tz = tz*2
+                    end
+                    local v = -1
+                    if v1 > thresh then
+                        v = v1;
+                        area = area + 1
+                    end
+                    if file then
+                        local c = math.max(0, math.min(255, v * 127 + 128))
+                        arr[2*x+1] = c
+                        arr[2*x+2] = c
+                    end
+                end
+                if file then
+                    line = line..string.char(table.unpack(arr))
+                end
+            end
+            if file then
+                file:write(line,line)
+            end
+        end
+    end
+
+    return area/4/(48*4)/(48*4)
+end
+
+function search(fn,min,max,goal,eps)
+    while true do
+        local center = (max+min)/2
+        local cval = fn(center)
+        print('At '..center..': '..cval)
+        if math.abs(cval-goal) < eps then
+            return center
+        end
+        if cval > goal then
+            min = center
+        else
+            max = center
+        end
+    end
+end
+
+local thresh = search(render, -1, 1, goal, 0.001)
+
+local file,err = io.open(fname, 'wb')
+if not file then
+    print('error: ',err)
+    return
+end
+file:write('P5\n768 768\n255\n')
+local area = render(thresh, file)
+file:close()
+
+print('Area fraction: '..area)