paint.lua

local fenster = require('fenster')

---Draw a line between two points (window boundary version)
---@param window window*
---@param x0 integer
---@param y0 integer
---@param x1 integer
---@param y1 integer
---@param color integer
local function draw_line(window, x0, y0, x1, y1, color)
	local window_width = window.width
	local window_height = window.height
	local dx = math.abs(x1 - x0)
	local dy = math.abs(y1 - y0)
	local sx = x0 < x1 and 1 or -1
	local sy = y0 < y1 and 1 or -1
	local err = (dx > dy and dx or -dy) / 2
	local e2 ---@type number
	while true do
		-- NOTE: If you are copying this code, you may want to remove this boundary check
		if x0 >= 0 and x0 < window_width and y0 >= 0 and y0 < window_height then
			window:set(x0, y0, color)
		end

		if x0 == x1 and y0 == y1 then
			break
		end

		e2 = err
		if e2 > -dx then
			err = err - dy
			x0 = x0 + sx
		end
		if e2 < dy then
			err = err + dx
			y0 = y0 + sy
		end
	end
end

---Fill an area with a specific color
---@param window window*
---@param x integer
---@param y integer
---@param color integer
---@param old_color integer?
local function fill(window, x, y, color, old_color)
	old_color = old_color or window:get(x, y)
	if old_color == color then
		return
	end

	local window_width = window.width
	local window_height = window.height
	local stack = { (y * window_width) + x }
	while stack[1] do
		local pos = table.remove(stack)
		x = pos % window_width ---@type integer
		y = math.floor(pos / window_width)
		if window:get(x, y) == old_color then
			window:set(x, y, color)

			if x > 0 then
				stack[#stack + 1] = pos - 1
			end
			if x < window_width - 1 then
				stack[#stack + 1] = pos + 1
			end
			if y > 0 then
				stack[#stack + 1] = pos - window_width
			end
			if y < window_height - 1 then
				stack[#stack + 1] = pos + window_width
			end
		end
	end
end

-- Define the keyboard keys and their corresponding colors
local key_color_map = {
	[48] = 0x000000, -- 0 (black)
	[49] = 0xffffff, -- 1 (white)
	[50] = 0x0000ff, -- 2 (blue)
	[51] = 0x00ff00, -- 3 (green)
	[52] = 0x00ffff, -- 4 (cyan)
	[53] = 0xff0000, -- 5 (red)
	[54] = 0xff00ff, -- 6 (magenta)
	[55] = 0xffff00, -- 7 (yellow)
	[56] = 0x808080, -- 8 (gray)
	[57] = 0xFFA500, -- 9 (orange)
}

-- Define the key for the fill action
local fill_key = 70 -- F Key

-- Open a window
local window_width = 640
local window_height = 360
local window = fenster.open(
	window_width,
	window_height,
	'Paint Demo - Press ESC to exit, 0-9 to change color, F to fill'
)

-- Main loop
local paint_color = key_color_map[49]
local last_mouse_x ---@type integer?
local last_mouse_y ---@type integer?
while window:loop() and not window.keys[27] do
	local keys = window.keys

	-- Check if a color key is pressed
	for key, color in pairs(key_color_map) do
		if keys[key] then
			-- Set the color to the assigned key color
			paint_color = color
		end
	end

	local mouse_x = window.mousex
	local mouse_y = window.mousey
	local mouse_down = window.mousedown

	if mouse_down then
		-- Draw a line between the last mouse position and the current mouse position
		-- (Uses current mouse position if last mouse position is not set)
		draw_line(
			window,
			last_mouse_x or mouse_x,
			last_mouse_y or mouse_y,
			mouse_x,
			mouse_y,
			paint_color
		)

		-- Update the last mouse position
		last_mouse_x, last_mouse_y = mouse_x, mouse_y
	elseif last_mouse_x and last_mouse_y then
		-- Reset the last mouse position
		last_mouse_x, last_mouse_y = nil, nil
	elseif keys[fill_key] then
		-- Fill the area at the mouse position
		fill(window, mouse_x, mouse_y, paint_color)

		-- Wait until fill key released
		while window:loop() and window.keys[fill_key] do
			--
		end
	end
end