create-bitmap-font

Create a bitmap sprite font in node

npm install @nrkn/create-bitmap-font

In the example we create a bitmap font and then use it to draw some text:

import { promises } from 'fs'
import { createBitmapFont, drawText } from '@nrkn/create-bitmap-font'

const { readFile, writeFile } = promises

// colors - 4 bytes in rgba order
const fill = [0xff, 0xc2, 0x0e, 0xff]
const bg = [ 0, 0, 0, 0 ]

const start = async () => {
  // let's just use the printable chars from 7-bit ascii
  // eg [ 33, 34, ...etc ]
  const codes = createSeq(95, i => i + 33)

  // otf or ttf buffer
  const font = await readFile('some-font.otf')

  const bitmapFont = createBitmapFont(font, 32, { fill, bg, codes })

  const { offsets, pngBuffer } = bitmapFont

  // save the bitmap font and the text metrics
  await writeFile( 'some-font.png', pngBuffer )
  await writeFile( 'some-font.json', JSON.stringify( offsets, null, 2 ), 'utf8' )

  // create text drawing function
  const draw = drawText( bitmapFont.canvas, bitmapFont.offsets )

  // first we will create a round trip and see if it matches the font bitmap

  const text = codes.map( c => String.fromCharCode( c ) ).join( '' )

  // returns a canvas
  const roundTrip = draw( text )

  // turn it into a PNG
  const roundPng = roundTrip.toBuffer('image/png')

  // should be the same as the pngBuffer created by createBitmapFont
  await writeFile( 'test-round.png', roundPng )

  // now write some arbitrary text

  const testText = 'Hello, world'

  const testDraw = draw( testText )

  const testPng = testDraw.toBuffer( 'image/png' )

  await writeFile( 'test-out.png', testPng )
}

const createSeq = (length, cb) =>
  Array.from({ length }, (_v, k) => cb(k))

start().catch(console.error)

todo

Should be able to use in browser too, especially as we are using a canvas compatible module in node - add a factory function that takes deps like canvas etc and returns a create bitmap font function

Using measureText to get the metrics is lazy - we have plenty of code lying around that can get better metrics by parsing the font file, eg proper x advance, kerning etc - but this gets job done for now

license

MIT License

Copyright (c) 2022 Nik Coughlin

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.