dom-to-data-url.ts

import { changeJpegDpi } from '../change-jpeg-dpi'
import { changePngDpi, detectPhysChunkFromDataUrl } from '../change-png-dpi'
import { orCreateContext } from '../create-context'
import { SUPPORT_ATOB, SUPPORT_BTOA } from '../utils'
import { domToCanvas } from './dom-to-canvas'
import type { Context } from '../context'
import type { Options } from '../options'

export async function domToDataUrl<T extends Node>(node: T, options?: Options): Promise<string>
export async function domToDataUrl<T extends Node>(context: Context<T>): Promise<string>
export async function domToDataUrl(node: any, options?: any) {
  const context = await orCreateContext(node, options)
  const { log, quality, type, dpi } = context
  const canvas = await domToCanvas(context)
  log.time('canvas to data url')
  let dataUrl = canvas.toDataURL(type, quality)
  if (
    ['image/png', 'image/jpeg'].includes(type)
    && dpi
    && SUPPORT_ATOB
    && SUPPORT_BTOA
  ) {
    const [format, body] = dataUrl.split(',')
    let headerLength = 0
    let overwritepHYs = false
    if (type === 'image/png') {
      const b64Index = detectPhysChunkFromDataUrl(body)
      // 28 bytes in dataUrl are 21bytes, length of phys chunk with everything inside.
      if (b64Index >= 0) {
        headerLength = Math.ceil((b64Index + 28) / 3) * 4
        overwritepHYs = true
      } else {
        headerLength = 33 / 3 * 4
      }
    } else if (type === 'image/jpeg') {
      headerLength = 18 / 3 * 4
    }
    // 33 bytes are ok for pngs and jpegs
    // to contain the information.
    const stringHeader = body.substring(0, headerLength)
    const restOfData = body.substring(headerLength)
    const headerBytes = window.atob(stringHeader)
    const uint8Array = new Uint8Array(headerBytes.length)
    for (let i = 0; i < uint8Array.length; i++) {
      uint8Array[i] = headerBytes.charCodeAt(i)
    }
    const finalArray = type === 'image/png'
      ? changePngDpi(uint8Array, dpi, overwritepHYs)
      : changeJpegDpi(uint8Array, dpi)
    const base64Header = window.btoa(String.fromCharCode(...finalArray))
    dataUrl = [format, ',', base64Header, restOfData].join('')
  }
  log.timeEnd('canvas to data url')
  return dataUrl
}