Useful Snippets

[jonasgeiler]

In this discussion I will collect many useful snippets for the lua-fenster library that I have come across. These snippets should be relatively short and general. Feel free to post your own snippets!

[jonasgeiler]

Basic window loop

A very basic window loop that exits when the Escape key is pressed:

while window:loop() and not window.keys[27] do
	-- Do stuff here
end 

[jonasgeiler]

Key code map

Here is a very basic key code map:

local keys = {
	backspace = 8,
	tab = 9,
	enter = 10,
	arrow_up = 17,
	arrow_down = 18,
	arrow_right = 19,
	arrow_left = 20,
	escape = 27,
	space = 32,
	["'"] = 39,
	[','] = 44,
	['-'] = 45,
	['.'] = 46,
	['/'] = 47,
	['0'] = 48,
	['1'] = 49,
	['2'] = 50,
	['3'] = 51,
	['4'] = 52,
	['5'] = 53,
	['6'] = 54,
	['7'] = 55,
	['8'] = 56,
	['9'] = 57,
	a = 65,
	b = 66,
	c = 67,
	d = 68,
	e = 69,
	f = 70,
	g = 71,
	h = 72,
	i = 73,
	j = 74,
	k = 75,
	l = 76,
	m = 77,
	n = 78,
	o = 79,
	p = 80,
	q = 81,
	r = 82,
	s = 83,
	t = 84,
	u = 85,
	v = 86,
	w = 87,
	x = 88,
	y = 89,
	z = 90,
	['['] = 91,
	['\\'] = 92,
	[']'] = 93,
	['`'] = 96,
	delete = 127,
}

-- Usage
if window.keys[keys.enter] then
	-- Enter key is pressed
end

There might be some keys missing. Let me know if you find one!

Tip

Some key codes can also be retrieved using the string.byte() function:

local f_key = string.byte('F') -- returns 70

[jonasgeiler]

Calculate FPS

Calculating the FPS to measure performance is super easy with the window delta:

local fps = 1 / window.delta

[jonasgeiler]

Drawing rectangles

Here is a simple function to draw rectangles:

local function draw_rectangle(window, x, y, width, height, color)
	local dx_end = x + width - 1
	for dy = y, y + height - 1 do
		for dx = x, dx_end do
			window:set(dx, dy, color)
		end
	end
end

[jonasgeiler]

Drawing circles

Here is a simple function to draw circles:

local function draw_circle(window, x, y, radius, color)
	local radius_neg = -radius
	local radius_pow2 = radius * radius
	for dy = radius_neg, radius do
		local dy_pow2 = dy * dy
		local sy = y + dy
		for dx = radius_neg, radius do
			if dx * dx + dy_pow2 < radius_pow2 then
				window:set(x + dx, sy, color)
			end
		end
	end
end

[jonasgeiler]

Drawing lines

Here is a simple function to draw lines:

local function draw_line(window, x0, y0, x1, y1, color)
	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
	while true do
		window:set(x0, y0, color)

		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

[jonasgeiler]

Loading and drawing images

Images are a bit more complex to load and draw. I recommend using a very simple image format like Netpbm PPM (P3 or P6) to store the image in a file. A PPM image is basically just a raw list of RGB values with the file header at the start.

Here's the command for ImageMagick to convert a PNG to PPM:

magick image.png -depth 8 image.ppm

You could use GIMP as well, but unfortunately GIMP adds a comment to the header of the PPM file, which makes it a bit more complicated to parse compared to the ImageMagick output.

Here is a very simple code to load such a PPM (P6) image:

local function load_image(path)
	local image = assert(io.open(path, 'rb'))

	local image_type = image:read(2)
	assert(image_type == 'P6', 'Invalid image type: ' .. tostring(image_type))
	assert(image:read(1), 'Invalid image header') -- Whitespace
	local image_width = image:read('*number')
	assert(image_width, 'Invalid image width: ' .. tostring(image_width))
	assert(image:read(1), 'Invalid image header') -- Whitespace
	local image_height = image:read('*number')
	assert(image_height, 'Invalid image height: ' .. tostring(image_height))
	assert(image:read(1), 'Invalid image header') -- Whitespace
	local image_max_color = image:read('*number')
	assert(
		image_max_color == 255,
		'Invalid image maximum color: ' .. tostring(image_max_color)
	)
	assert(image:read(1), 'Invalid image header') -- Whitespace

	local image_buffer = {}
	while true do
		local r_raw = image:read(1)
		local g_raw = image:read(1)
		local b_raw = image:read(1)
		if not r_raw or not g_raw or not b_raw then
			break
		end

		local r = string.byte(r_raw)
		local g = string.byte(g_raw)
		local b = string.byte(b_raw)
		table.insert(image_buffer, fenster.rgb(r, g, b))
	end

	image:close()
	return image_buffer, image_width, image_height
end

And here is a function to draw the loaded image:

local function draw_image(window, x, y, image_buffer, image_width, image_height)
	local ix_end = image_width - 1
	for iy = 0, image_height - 1 do
		local dy = y + iy
		local iy_index = iy * image_width + 1
		for ix = 0, ix_end do
			window:set(x + ix, dy, image_buffer[iy_index + ix])
		end
	end
end

[jonasgeiler]

Drawing text

Since most text drawing functions require large tables of font data I will not include one here for now. Check out the text-editor demo for an example on drawing text. It includes the microknight font and a function to draw text.