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

Reader/Writer for png chunk pHYs on browsers

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.isPng = isPng;
exports.readBytes = readBytes;
exports.readIHDR = readIHDR;
exports.getCharCodes = getCharCodes;
exports.convertToDataURI = convertToDataURI;
exports.convertToByteArray = convertToByteArray;
exports.toHex = exports.toBin = void 0;

var toBin = function toBin(value, digits) {
  return value.toString(2).padStart(digits, '0');
};

exports.toBin = toBin;

var toHex = function toHex(value, digits) {
  return value.toString(16).padStart(digits, '0');
};

exports.toHex = toHex;

function isPng(byteArray, ptr) {
  var pngSignature = '89 50 4E 47 0D 0A 1A 0A';
  var signature = readBytes(byteArray, ptr, 8).map(function (v) {
    return toHex(v, 2);
  });
  return signature.join(' ').toUpperCase() === pngSignature;
}

function readBytes(byteArray, ptr, byteLength) {
  var pos = ptr.pos;
  var res = byteArray.slice(pos, pos + byteLength);
  ptr.pos += byteLength;
  return Array.from(res);
}

function readIHDR(byteArray, ptr) {
  // https://tools.ietf.org/html/rfc2083#page-15
  // Length, ChunkType
  ptr.pos += 4 + 4;
  var width = readBytes(byteArray, ptr, 4).map(function (v) {
    return toBin(v, 8);
  });
  width = parseInt(width.join(''), 2);
  var height = readBytes(byteArray, ptr, 4).map(function (v) {
    return toBin(v, 8);
  });
  height = parseInt(height.join(''), 2); // Bit depth, Color type, Compression method, Filter method, nterlace method, CRC

  ptr.pos += 1 + 1 + 1 + 1 + 1 + 4;
  return {
    width: width,
    height: height
  };
}

function getCharCodes(str) {
  return str.split('').map(function (c) {
    return c.charCodeAt(0);
  }).join(' ');
}

var dataURIScheme = 'data:image/png;base64,';

function convertToDataURI(arrayBuffer) {
  var byteArray = new Uint8Array(arrayBuffer);
  return dataURIScheme + btoa(byteArray.reduce(function (data, byte) {
    return data + String.fromCharCode(byte);
  }, ''));
}

function convertToByteArray(dataURI) {
  if (!dataURI.startsWith(dataURIScheme)) return [];
  var rawStr = atob(dataURI.split(dataURIScheme)[1]);
  var array = new Uint8Array(new ArrayBuffer(rawStr.length));

  for (var i = 0; i < rawStr.length; i++) {
    array[i] = rawStr.charCodeAt(i);
  }

  return array;
}