kettek / ico-endec-js

WIP ICO encoder and decoder

ICO encoder & decoder

This JavaScript library provides an encoder and decoder for ICO and CUR files. Although this library can encode and decode both BMP and PNG images, BMP endec does not provide bitmasking support, and as such, will not work with some icons. However, PNG support is widespread and has become a more defacto standard for application icons, so this problem is largely moot -- but it still would be nice to have.

Encoding

icoEndec.encode([Buffer||ArrayBuffer])

The encode function takes an array of ArrayBuffers or Buffers that contain BMP or PNG data. It returns a Buffer containing the binary data of the ICO file.

Example

const icoEndec   = require('ico-endec')
const fsPromises = require('fs').promises

;(async () => {
  let icoBuffer = icoEndec.encode([
    await fsPromises.readFile('myIcon-16x16.png'),
    await fsPromises.readFile('myIcon-32x32.png'),
    await fsPromises.readFile('myIcon-64x64.png')
  ])
  
  await fsPromises.writeFile('myIcon.ico', icoBuffer)
})()

Decoding

icoEndec.decode(Buffer)

The decode function takes a Buffer or an ArrayBuffer that holds the binary data of an ICO file. It returns an array of IconEntries.

Example

const icoEndec   = require('ico-endec')
const fsPromises = require('fs').promises

;(async () => {
  let icons = icoEndec.decode(await fsPromises.readFile('myIcon.ico'))
  
  icons.forEach((icon, index) => {
    fsPromises.writeFile(`myIcon-${icon.width}x${icon.height}.${icon.imageType}`, icon.imageData)
  })
})()

IconEntry

The IconEntry class stores various information about the given icon entry.

Accessor	Type	Description
width	Number	width of the image, maximum of 256
height	Number	height of the image, maximum of 256
colors	Number	number of colors
colorPlanes	Number	color planes of an ICO image
bitsPerPixel	Number	bits per pixel of an ICO image
horizontalHotspot	Number	horizontal hotspot of a CUR image
verticalHotspot	Number	vertical hotspot of a CUR image
imageSize	Number	(interal) size of imageData's buffer
imageOffset	Number	(interal) offset start of the image data
imageType	String	'png' or 'bmp'
imageData	Buffer	image data of the icon

ico-endec-js's Issues

Palette chunk check starts at wrong index

ico-endec-js/src/encoder.js

Line 76 in e8e0ff3

if (imageData[29] !== 'P' && imageData[30] !== 'L' && imageData[31] !== 'T' && imageData[32] !== 'E') {

The indexes for the PLTE-chunk check are wrong. They should be further, depending on the length of the IHDR-chunk + the 4 byte CRC of that chunk (see specification).

In this case, it should skip 4 bytes (CRC of the IHDR-chunk) and another 4 bytes (the size indicator of the PLTE-chunk).

Check out my visual helper for PNG.