png-dpi-reader-writer/lib/writer.js

Reader/Writer for png chunk pHYs on browsers

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.writePngDpi = writePngDpi;

var _crc = require("./crc32");

var _share = require("./share");

function _toConsumableArray(arr) { return _arrayWithoutHoles(arr) || _iterableToArray(arr) || _nonIterableSpread(); }

function _nonIterableSpread() { throw new TypeError("Invalid attempt to spread non-iterable instance"); }

function _iterableToArray(iter) { if (Symbol.iterator in Object(iter) || Object.prototype.toString.call(iter) === "[object Arguments]") return Array.from(iter); }

function _arrayWithoutHoles(arr) { if (Array.isArray(arr)) { for (var i = 0, arr2 = new Array(arr.length); i < arr.length; i++) { arr2[i] = arr[i]; } return arr2; } }

function bytes(num, byteLength) {
  var binStr = num.toString(2).padStart(byteLength * 8, '0');
  var binArr = binStr.match(/\d{8}/g);
  return binArr.map(function (v) {
    return parseInt(v, 2);
  });
}

function insertChunkPhys(byteArray, ptr) {
  var dpi = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : 72;
  var type = 'pHYs'.split('').map(function (c) {
    return c.charCodeAt(0);
  }); // Number of pixels per unit when DPI is 72
  // Number of pixels per unit when devicePixelRatio is 1

  var PX_PER_METER = 2835;
  var dpr = dpi / 72;
  var pixelsPerMeter = Math.floor(PX_PER_METER * dpr);
  var data = [].concat(_toConsumableArray(bytes(pixelsPerMeter, 4)), _toConsumableArray(bytes(pixelsPerMeter, 4)), [1]);
  var pHYsChunk = [0, 0, 0, 9].concat(_toConsumableArray(type), _toConsumableArray(data), _toConsumableArray(bytes((0, _crc.crc)([].concat(_toConsumableArray(type), _toConsumableArray(data))), 4)));
  var pos = ptr.pos - 8;
  var newByteArray = new Uint8Array([].concat(_toConsumableArray(Array.from(byteArray.slice(0, pos))), _toConsumableArray(pHYsChunk), _toConsumableArray(Array.from(byteArray.slice(pos)))));
  ptr.pos += pHYsChunk.length;
  return newByteArray;
}

function writePngDpi(arrayBuffer) {
  var dpi = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 72;
  var ptr = {
    pos: 0
  };
  var byteArray = new Uint8Array(arrayBuffer);
  if (!(0, _share.isPng)(byteArray, ptr)) return byteArray;
  (0, _share.readIHDR)(byteArray, ptr);
  var hasChunkPhys = false;
  var newByteArray;

  while (true) {
    if (ptr.pos >= byteArray.length) break;
    var chunkLength = (0, _share.readBytes)(byteArray, ptr, 4).map(function (v) {
      return (0, _share.toBin)(v, 8);
    });
    chunkLength = parseInt(chunkLength.join(''), 2);
    var chunkType = (0, _share.readBytes)(byteArray, ptr, 4).join(' ');

    if (chunkType === (0, _share.getCharCodes)('IDAT')) {
      if (!hasChunkPhys) {
        newByteArray = insertChunkPhys(byteArray, ptr, dpi);
        hasChunkPhys = true;
      }

      break;
    }

    if (chunkType === (0, _share.getCharCodes)('IEND')) break;

    switch (chunkType) {
      case (0, _share.getCharCodes)('pHYs'):
        hasChunkPhys = true;
    }

    ptr.pos += chunkLength + 4; // CRC
  }

  return newByteArray || byteArray;
}