A list of helpful libraries and code

Riiiiight, that makes sense! I thought the self was probably not referring to anything; but I’d tried just passing in nil and, as you say, it’s not designed for that!

BUT I would like to say that this has been SO helpful. I used it to set up dialogue event triggers based on different state changes, and am seeing other places to use it immediately. I remain so grateful to you for sharing your experiments and knowledge, @dustin! :smiley:

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@nic trying your first round function math.round(number, precision) and negative numbers are printing inprecise, eg. -1 as -1.0000000001

results from nic (new) math.round(number, bracket) version are good though!

Found this helpful when constructing patterns for drawing with.

function utils.printPattern(rows_of_bits)
  local pattern = {}
  for k, row in ipairs(rows_of_bits) do
    local bit_position = #row
    local row_value = 0x00
    for i, bit in ipairs(row) do
      if bit == 1 then
        row_value = row_value + (math.pow(2, bit_position)//2)
      bit_position -= 1
    pattern[#pattern + 1] = row_value
  local print_string = "{ "
  for i, v in pairs(pattern) do
    print_string = print_string .. string.format("0x%02X", v)
    if i < #pattern then
      print_string = print_string .. ", "
  print_string = print_string .. " }"

Which allows me to prototype a pattern in code quick and output a value that I can pass into, say, playdate.graphics.setPattern(...).

		{1, 1, 1, 1, 1, 1, 1, 1},
		{1, 1, 1, 1, 1, 1, 1, 1},
		{0, 0, 0, 0, 0, 0, 0, 0},
		{0, 0, 0, 0, 0, 0, 0, 0},
		{1, 1, 1, 1, 1, 1, 1, 1},
		{1, 1, 1, 1, 1, 1, 1, 1},
		{0, 0, 0, 0, 0, 0, 0, 0},
		{0, 0, 0, 0, 0, 0, 0, 0}


{ 0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00 }

If there is an easier way to do this, I will not be surprised. :wink:

@dustin I just don’t bother with the hex at all: https://devforum.play.date/t/matts-prototypes/826/4?u=matt


HAHA tonumber has a optional base param :playdate_shocked:

Thanks! I’ll just delete all of this now.

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To work with patterns in the Playdate, I recommend using this small tool: https://www.ivansergeev.com/gfxp/
I hope it will be useful to you.


This little snippet saved my sanity. It means you don’t have to manage the dimensions and initialisation when using tables as multi-dimensional arrays in Lua.

from: https://stackoverflow.com/a/21287623/28290

function newAutotable(dim)
    local MT = {};
    for i=1, dim do
        MT[i] = {__index = function(t, k)
            if i < dim then
                t[k] = setmetatable({}, MT[i+1])
                return t[k];

    return setmetatable({}, MT[1]);

-- Usage
local at = newAutotable(3);
print(at[0]) -- returns table
print(at[0][1]) -- returns table
print(at[0][1][2]) -- returns nil
at[0][1][2] = 2;
print(at[0][1][2]) -- returns value
print(at[0][1][3][3]) -- error, because only 3 dimensions set

I just discovered the strict mode script in lua that check if the variables you use have been properly initialized. It is useful to prevent making typos in your variable that can go easily unnoticed and create bugs.


In my code I just added a check so that it would be used only in the simulator

-- strict.lua
-- checks uses of undeclared global variables
-- All global variables must be 'declared' through a regular assignment
-- (even assigning nil will do) in a main chunk before being used
-- anywhere or assigned to inside a function.
-- distributed under the Lua license: http://www.lua.org/license.html

if not playdate.isSimulator then

local getinfo, error, rawset, rawget = debug.getinfo, error, rawset, rawget

local mt = getmetatable(_G)
if mt == nil then
  mt = {}
  setmetatable(_G, mt)

mt.__declared = {}

local function what ()
  local d = getinfo(3, "S")
  return d and d.what or "C"

mt.__newindex = function (t, n, v)
  if not mt.__declared[n] then
    local w = what()
    if w ~= "main" and w ~= "C" then
      error("assign to undeclared variable '"..n.."'", 2)
    mt.__declared[n] = true
  rawset(t, n, v)
mt.__index = function (t, n)
  if not mt.__declared[n] and what() ~= "C" then
    error("variable '"..n.."' is not declared", 2)
  return rawget(t, n)

Update: It seems this piece of code is actually already in the SDK you just have to import 'CoreLibs/strict'


This is random but I just wrote this function to generate an array of midi notes. Maybe someone some day will find it useful besides me.

function generateMidiNotes(octave, offset, note_count, reverse_order)
	local base <const> = {24, 26, 28, 29, 31, 33, 35}
	local notes = table.create(note_count)
	local index_start <const> = reverse_order and (note_count-1) or 0
	local index_end <const> = reverse_order and 0 or (note_count-1)
	local index_inc <const> = reverse_order and -1 or 1
	local note_i = 0
	for i = index_start, index_end, index_inc do
		notes[note_i + 1] = base[((offset + i) % #base) + 1] + (12 * (math.floor((offset + i) / #base) + octave))
		note_i += 1
	return notes

I’ll happily be your first customer on this one, Dustin : D
I’m having a hard time understanding how to generate good random musical scales for my game, it’s all very new to me.

1 Like

Here a very simple parser to get paths from a svg file.

It returns a table of paths which are tables or coordinate { x1, y1, x2, y2, x3, y3, … }

function getSvgPaths( svg_filepath )
	local file, file_error = playdate.file.open( svg_filepath, playdate.file.kFileRead )
	assert(file, "getSvgPaths(), Cannot open file", svg_filepath," (",file_error,")")

	local push = table.insert
	local commandArgCount = { M=2, L=2, T=2, H=1, V=1, C=6, S=6, A=7, Z=0}

	-- read the whole file
	local fileContent = ""
		local line = file:readline()
		if line then
			fileContent = fileContent..line
	until not line

	local result = table.create( 8 )
	for path in fileContent:gmatch("<path.-/>") do
		local previousX, previousY = 0, 0
		local newPath = table.create( 8 )

		local name = path:match("id=\"(.-)\"")
		if not name then name = #result + 1 end
		result[name] = newPath

		local d_content = path:match(" d=\"(.-)\"")
		for command in d_content:gmatch("%a[%-%d%., ]*") do
			local first_character = command:sub(1,1)
			local command_letter = first_character:upper()
			local absolute_coordinates = command_letter==first_character

			local args = table.create( 6 )
			for number in command:gmatch("[-%d%.]+") do
				push(args, tonumber(number))
			local argCount = commandArgCount[ command_letter ]

			local argIndex = 0
			while argIndex+argCount<=#args do
				local relativeX, relativeY = 0, 0
				if not absolute_coordinates then
					relativeX, relativeY = previousX, previousY

				if command_letter=="M" or command_letter=="L" or command_letter=="T" then
					push( newPath, args[argIndex+1] + relativeX)
					push( newPath, args[argIndex+2] + relativeY)
				elseif command_letter=="H" then
					push( newPath, args[argIndex+1] + relativeX)
					push( newPath, previousY)
				elseif command_letter=="V" then
					push( newPath, previousX)
					push( newPath, args[argIndex+1] + relativeY)
				elseif command_letter=="C" then
					push( newPath, args[argIndex+5] + relativeX)
					push( newPath, args[argIndex+6] + relativeY)
				elseif command_letter=="S" then
					push( newPath, args[argIndex+3] + relativeX)
					push( newPath, args[argIndex+4] + relativeY)
				elseif command_letter=="A" then
					push( newPath, args[argIndex+6] + relativeX)
					push( newPath, args[argIndex+7] + relativeY)
				elseif command_letter=="Z" then
					push( newPath, newPath[1])
					push( newPath, newPath[2])

				previousX = newPath[#newPath-1]
				previousY = newPath[#newPath]

				argIndex = argIndex + math.max(argCount, 1)

	for rect in fileContent:gmatch("<rect.-/>") do
		local width = tonumber( rect:match("width=\"([-%d%.]+)\"") )
		local height = tonumber( rect:match("height=\"([-%d%.]+)\"") )
		local x = tonumber( rect:match("x=\"([-%d%.]+)\"") )
		local y = tonumber( rect:match("y=\"([-%d%.]+)\"") )

		local name = rect:match("id=\"(.-)\"")
		if not name then name = #result + 1 end
		result[name] = {
			x, y,
			x+width, y,
			x+width, y+height,
			x, y+height,
			x, y,

	return result


  • Fix various bugs
  • return a hashmap with the names of the path
  • Increase compatibility
  • added support for rectangle primitive

So when I was working on the LDtk level loader, something that was bothering me was that parsing a level was not fast enough. To solve this issue, after reading a level, I was exporting the result in a lua file that can be used instead of the json file.

I wanted to share a simpler version of this that could be used more generally. But the general idea:

  1. When running in the simulator, after parsing a file we write the result as a lua file in the save folder (In the SDK folder)
  2. The lua file is copied in the project folder
  3. When running on the console if the lua file is present, load it instead of parsing the file
  4. Save the frame!

The first piece of the puzzle is the following function that export a table as a lua file

function writeLua( filepath, table_to_export )
	assert( filepath, "writeLua, filepath required")
	assert( table_to_export, "writeLua, table_to_export required")

	local file, file_error = playdate.file.open( filepath, playdate.file.kFileWrite)
	if not file then
		print("writeLua, Cannot open file ", filepath," (", file_error, ")")

	local _isArray = function( t )
		if type(t[1])=="nil" then return false end

		local pairs_count = 0
		for key in pairs(t) do
			pairs_count = pairs_count + 1
			if type(key)~="number" then
				return false

		return pairs_count==#t

	local _write_entry
	_write_entry = function( entry, name )
		local entry_type = type(entry)

		if entry_type=="table" then
			if _isArray( entry ) then
				for key, value in ipairs(entry) do
					_write_entry(value, key)
				for key, value in pairs(entry) do
					_write_entry(value, key)
		elseif entry_type=="string" then
		elseif entry_type=="boolean" or entry_type=="number" then

	file:write("return ")
	_write_entry( table_to_export )


To actually parse or load the lua file directly I have the following code

-- set _enable to false to always load the original file
local _enable = true

-- folder in the project folder where the pre parsed file will be
local _folder = "preParsed/"

function parseFile( parser_fn, filename, ...)
	local pdzFilename = _folder..filename..".pdz"

	if _enable then
		if playdate.file.exists( pdzFilename ) then
			return playdate.file.run( pdzFilename )
			print( "parseFile(): The following file is not pre-parsed", filename)

	return parser_fn( filename, ...)

if playdate.isSimulator then
	parseFile = function( parser_fn, filename, ...)
		local result = parser_fn( filename, ...)

		-- save result in lua file
		local luaFilename = _folder..filename..".lua"
		playdate.file.mkdir( luaFilename:match("^(.-)[^/]*$") )
		writeLua( luaFilename, result)

		return result

To use it I simply replace a call to a parsing function with it

So for example instead of
level = json.decodeFile( "level_1-1.json" )

I would call it this way
level = parseFile( json.decodeFile, "level_1-1.json" )

Using “level_1-1.json” from the SDK example as a comparaison, loading the pre-parsed lua file is 5 times faster on the playdate than parsing the json file normally. For the svg parser I posted earlier the advantage is even more pronounced since this is 10 times faster.

Big caveats
The biggest drawback of this technique is that you need to be aware of the cached files otherwise you might have edit the original file and the game will still load the previous pre-parsed version. It get even trickier since at the moment files are not deleted when uploading a game to the playdate (so you might delete all the pre-parsed in your project but on playdate it will still load some file you don’t even know are still there)

I created a symbolic link in my save folder to the “preParsed/” folder in my project so that I don’t have to manually copy the files.
I also wrote a function in my project to pre-parsed all files in one go. Right now I call it when the game start since there is not that much files but later I might simply call it from the simulator console when I need to create a build.

Really useful, Nic. Thanks!

In my build process I manage something similar by copying the timestamp from the original file to the processed file. Then I compare file timestamps to see if I need to reprocess the file.

But I don’t think it’s currently possible to do this on the device using standard SDK/Lua functions. SDK can at least get modified timestamp but can’t set it.

Might make a good feature request.

This is something I experimented with. The best solution I came up with was to have a symbolic link to the whole project folder in the save folder to be able to check the file modification time for the original file, not the one in the pdx.
But requiring proper setup of the save folder for the feature to work, I thought is was getting over-complicated so I preferred a simpler solution.

I would actually prefer to have full read/write access to my project folder to be honest, that would work way better (similar to playdate.simulator.writeToFile(image, path)). But when I thought about it, would I want all game running in the simulator to have full access to my files? mmmh not really.

Put together a tiny Playdate utility to experiment with the built-in easing functions. It’s a single lua file, easy to build and run on device. Not a bad way to tune animations and experiment with additional ease settings like softness for back and amplitude/period for elastic. Also nice to get a sense of how an animation may feel on device.

main.lua.zip (2.6 KB)

up/down change selected setting.
right/left change selected value.
hold A while pressing left/right to change selected value by smaller increments.
press A to run animation again.



Just used this for the first time and it worked great! I had an issue trying to unsubscribe when I was using an anonymous function.

A simple solution I found while looking at similar libs is to return the function that was passed to the subscribed function and then use that for unsubscribing.

function Signal:subscribe(key, bind, fn)
	local t = self.listeners[key]
	local v = {fn = fn, bind = bind}
	if not t then
		self.listeners[key] = {v}
		t[#t + 1] = v
	return fn

And then

function Init()
	self.fn = signal:subscribe(
		"eye-colected", self, function(ref, event, x, y, eyesQuota, index)

function Remove()
	signal:unsubscribe("eye-colected", self.fn)
1 Like

Thanks for this. I’ll think about this a bit!

Here is a set of helpers I found useful while working in C, you need to initialize asap and not use until you have initialized or you will get crashes. Doing it first thing in the event handler should be fine.



#include "pd_api.h"

void initializeMemoryTools(PlaydateAPI *playdate);

static void* pd_malloc(size_t size);
static void* pd_calloc(size_t count, size_t size);
static void* pd_realloc(void* ptr, size_t size);
static void  pd_free(void* ptr);



#include "pd_memory_tools.h"

static void* pd_realloc(void* ptr, size_t size) {
    return pd->system->realloc(ptr, size);

static void* pd_malloc(size_t size) {
    return pd_realloc(NULL, size);

static void* pd_calloc(size_t count, size_t size) {
    return memset(pd_malloc(count * size), 0, count * size);

static void pd_free(void* ptr) {
    pd_realloc(ptr, 0);

static PlaydateAPI *pd = NULL;
void initializeMemoryTools(PlaydateAPI *playdate) {
    pd = playdate;

Online Json to lua table converter: JSON Lua table converter - MAGEDDO

I use this for static level data. I put the lua files in my source folder and load the resulting pdz that pdc automatically creates with file.run


Here's a lightweight drop-in replacement for playdate.graphics.image that adds support for animated images: Lightweight AnimatedImage Library