lua-pngencoder

Extremely simple PNG encoder for Lua. Inspired (read: directly transpiled) from https://www.nayuki.io/page/tiny-png-output

Usage

Import into your project, change usage of bit library to whatever suits your platform (by default it uses LuaJIT compatible bit library), use like this:

local encode = require "pngencoder"

local png = encode(64, 64) -- width, height
png:write { 0xFF, 0, 0 } -- RGB(255, 0, 0) pixel at 0x0
png:write { 0, 0xFF, 0 } -- RGB(0, 255, 0) pixel at 1x0
-- TODO: write rest of the pixels to fill rest of the 64x64 canvas

assert(png.done) -- just a failsafe to make sure we've filled the whole allocated PNG space

local data = png.output -- table containing raw PNG data

Note that the output table is populated in streaming fashion as you call write. You must write all the width * height * 3 bytes before doing anything with the output to make sure the footer is properly written and the PNG file is complete. You can use the done flag to make sure you're done writing.

It's also possible to write RGBA data:

local encode = require "pngencoder"

local png = encode(64, 64, "rgba") -- width, height, colorMode
png:write { 0xFF, 0, 0, 0x80 } -- RGB(255, 0, 0, 128) pixel at 0x0 (half transparent)
png:write { 0, 0xFF, 0, 0 }    -- RGB(0, 255, 0, 0)   pixel at 1x0 (fully transparent)
-- TODO: write rest of the pixels to fill rest of the 64x64 canvas

assert(png.done) -- just a failsafe to make sure we've filled the whole allocated PNG space

local data = png.output -- table containing raw PNG data