EXTernal PALette transFORM .LUA - Aseprite script prototype, version 1

ext_pal_xform.lua

-- EXTernal PALette transFORM .LUA - Aseprite script prototype, version 1
--   load sg2-format palette image
--   load sg2 sprite
--   validate
--   move between palette states by applying palette transformations

local dlg = Dialog { title = "External Palette Transformation  " }
local pal_img = nil
local pal_height_px = 0
local expected_palette_img_width = 256 -- TODO: this is hardcoded for now
local mode = "to_color" -- { "to_color", "to_greyscale" }
local palette_reverse_lookup = nil

-- TODO: support other sg2-format palette structures
-- dlg:radio {
-- 	id = "palette_structure_radio",
-- 	label = "Palette Structure",
-- 	text = "row-major 256-column left-to-right greyscale",
-- 	selected = true,
-- 	-- onclick = 
-- }

dlg:file {
	id = "palette_filename_input",
	label = "Palette File",
	title = "Open...",
	open = true,
	save = false,
	filename = "",
	filetypes = { "png" },
	onchange = function()
		-- load palette image
		pal_img = Image{ fromFile = dlg.data.palette_filename_input }
		pal_height_px = pal_img.height
		-- create lookup tables for each row
		palette_reverse_lookup = {}
		for y = 0, (pal_height_px - 1) do
			local pal_table = {}
			for pal_px in pal_img:pixels( Rectangle{ 0,y, expected_palette_img_width,1 }) do
				local pal_pixel_value = pal_px()
				pal_table[ pal_pixel_value ] = Color{ r = pal_px.x, g = pal_px.x, b = pal_px.x, a = 255 }
			end
			palette_reverse_lookup[ y ] = pal_table -- save
		end
		-- update gui
		dlg:modify {
			id = "palette_row_slider",
			max = (pal_height_px - 1),
			value = 1, -- also sort of shows user how many palette rows there are
			enabled = true,
		}
		dlg:modify {
			id = "go_button",
			enabled = true, -- ?
		}
	end,
}

dlg:slider {
	id = "palette_row_slider",
	label = "Palette Row",
	min = 0,
	max = pal_height_px,
	value = 0,
	visible = true,
	enabled = false,
}

dlg:radio {
	id = "transformation_mode_radio_to_color",
	label = "Mode",
	text = "Color",
	selected = true,
	onclick = function()
		mode = "to_color"
		dlg:modify {
			id = "transformation_mode_radio_to_color",
			selected = true
		}
		dlg:modify {
			id = "transformation_mode_radio_to_greyscale",
			selected = false
		}
	end,
}
dlg:radio {
	id = "transformation_mode_radio_to_greyscale",
	-- label = "Mode",
	text = "Greyscale",
	selected = false,
	onclick = function()
		mode = "to_greyscale"
		dlg:modify {
			id = "transformation_mode_radio_to_color",
			selected = false
		}
		dlg:modify {
			id = "transformation_mode_radio_to_greyscale",
			selected = true
		}
	end,
	-- enabled = false -- TODO: enable this when it is working properly
}

dlg:separator{}

function transform( px_color, mode, pal_img, selected_palette_row )
	if mode == "to_color" then
		-- TODO: validate px_color is a grey color (R==G==B)
		if px_color.red == px_color.blue and px_color.blue == px_color.green then
			-- is grey
			-- return the color of the pixel at palette_image location ( greyscale_value, palette_row )
			return Color( pal_img:getPixel( px_color.red, selected_palette_row ))
		else
			return px_color -- transformation unsuccessful; given color is not grey
		end
	elseif mode == "to_greyscale" then
		-- check lookup table
		local lookup_color = palette_reverse_lookup[ selected_palette_row ][ px_color.rgbaPixel ]
		if lookup_color then
			return lookup_color
		else
			return px_color -- transformation unsuccessful; given color not present in palette
		end
	end
end

dlg:button {
	id = "go_button",
	--label = ""
	text = "Apply",
	enabled = false,
	onclick = function()
		-- change to RGB (required for script to work, for now)
		app.command.ChangePixelFormat{ format="rgb" }
		local img = app.activeCel.image
		if not img then
			return print('No active image')
		end
		local img_new = Image( img ) -- clone active image
		-- execute transformation
		for px in img_new:pixels() do
			local px_color = Color( px() )
			local new_color = transform( px_color, mode, pal_img, dlg.data.palette_row_slider )
			px( app.pixelColor.rgba( new_color.red, new_color.green, new_color.blue, px_color.alpha ))
		end
		-- apply changes all at once
		img:drawImage( img_new )
		app.refresh()
	end,
}

dlg:show { wait = false }