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 (either the ASCII format, P3, or the raw/binary format, P6) to store the image in a file. A PPM image is basically just a list of RGB values with a simple file header at the start. No compression or other complicated features of more established image formats.
For example, my PPM loading function is only at like ~240 lines of code, but you could easily write a PPM loading function in ~30 lines of code. That's why PPM is a pretty popular image format in the graphics programming scene.

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 keep in mind that 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. Although, the PPM loading function I wrote can handle comments.

You can find my own PPM loading function in the ./demos/lib/ppm.lua file.
This function is adapted from the actual Netpbm source code and can therefore handle most, if not all, PPM files (P3 and P6).
Feel free to copy the file into your project and modify it to your needs!
It is also used by the image demo.

Here is a function to draw the loaded data returned from my PPM loading function:

local function draw_image(window, x, y, image_pixels, image_width, image_height)
	for iy = 1, image_height do
		local dy = y + (iy - 1)
		for ix = 1, image_width do
			window:set(x + (ix - 1), dy, image_pixels[iy][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.