commit 198532fd3b87d1210230e221be416b5d482d6547
Author: Jon Michael Aanes <jonjmaa@gmail.com>
Date:   Sun Jun 9 17:39:28 2019 +0200

    Initial commit of new palette swapping library. Uses `colors` library for certain functionality.

diff --git a/init.lua b/init.lua
new file mode 100644
index 0000000..7fe60d8
--- /dev/null
+++ b/init.lua
@@ -0,0 +1,134 @@
+
+local palette_swap = {}
+
+--------------------------------------------------------------------------------
+-- Main work functions
+
+local function get_palette_of_image_data (data)
+    assert(data)
+    --
+    local palette  = {}
+    local has_seen = {}
+    --
+    for x = 0, data:getWidth() - 1 do
+        for y = 0, data:getHeight() - 1 do
+            local r, g, b  =  data:getPixel(x, y)
+            if not has_seen[r]       then  has_seen[r]    = {}  end
+            if not has_seen[r][g]    then  has_seen[r][g] = {}  end
+            if not has_seen[r][g][b] then
+                local color = {r,g,b,a}
+                has_seen[r][g][b]    =  color
+                palette[#palette+1]  =  color
+            end
+        end
+    end
+    --
+    return palette
+end
+
+local function change_palette_to_dim_tree (change_palette)
+    assert(type(change_palette) == 'table')
+    --
+    local tree  =  {}
+    --
+    for color_from, color_to in pairs(change_palette) do
+        assert(type(color_from) == 'table')
+        assert(type(color_to)   == 'table')
+        --
+        local r, g, b  =  unpack(color_from)
+        if not tree[r]       then  tree[r]    = {}  end
+        if not tree[r][g]    then  tree[r][g] = {}  end
+        --
+        assert(not tree[r][g][b])
+        tree[r][g][b]    =  color_to
+    end
+    --
+    return tree
+end
+
+local function apply_change_palette (data, change_palette)
+    assert(data)
+    assert(change_palette)
+    --
+    local change_tree  =  change_palette_to_dim_tree(change_palette)
+    local function map (x, y, r, g, b, a)
+        local c  =  change_tree[r][g][b]
+        return c[1], c[2], c[3], a
+    end
+    --
+    local new_data = data:clone()
+          new_data:mapPixel(map)
+    --
+    return new_data
+end
+
+local function change_palette_from_map (map_func, palette)
+    local change_palette = {}
+    for i = 1, #palette do
+        local from  =  palette[i]
+        local to    =  {[4] = 1, map_func(unpack(from))}
+        change_palette[from] = to
+    end
+    return change_palette
+end
+
+--------------------------------------------------------------------------------
+-- API
+
+palette_swap.get_palette_from_image_data  = get_palette_of_image_data
+
+function palette_swap.apply_color_map_to_image_data (img_data, map_fn)
+    assert(img_data)
+    assert(type(map_fn) == 'function')
+    --
+    return apply_change_palette(img_data, change_palette_from_map(map_fn, get_palette_of_image_data(img_data)))
+end
+
+--------------------------------------------------------------------------------
+-- Example color maps
+
+palette_swap.color_map = {}
+
+function palette_swap.color_map.invert (r,g,b)
+    return 1 - r, 1 - g, 1 - b
+end
+
+function palette_swap.color_map.switch_channel (mode)
+    local channels = {'r', 'g', 'b'}
+    local channel_order = {}
+    for i = 1, #channels do
+        local index = (mode % #channels) + 1
+        mode = mode / #channels
+        channel_order[#channel_order+1] = table.remove(channels,index)
+    end
+
+    local func_s = ("return function (r, g, b)  return %s, %s, %s  end"):format(unpack(channel_order))
+    return loadstring (func_s)()
+end
+
+function palette_swap.color_map.rotate_hue (rad)
+
+    -- Only need to import colors when needed
+    local colors = require 'colors'
+    assert(type(colors) == 'table')
+    assert(type(colors.rgb1_to_rgb255) == 'function')
+    assert(type(colors.rgb_to_hsl) == 'function')
+    assert(type(colors.hsl_to_rgb1) == 'function')
+
+    -- Create function
+    return function (r, g, b)
+        local hsl = colors.rgb_to_hsl(colors.rgb1_to_rgb255(r, g, b))
+        --
+        hsl[1] = (hsl[1] + rad) % 1
+        --
+        local rgb1   = colors.hsl_to_rgb1(hsl)
+        return unpack(rgb1)
+    end
+end
+
+
+--------------------------------------------------------------------------------
+-- Return
+
+return palette_swap
+