src/utils/png.js
/**
* @author Robert Eisele <robert@xarg.org>
* @copyright Copyright (c) 2010, Robert Eisele
* @link http://www.xarg.org/2010/03/generate-client-side-png-files-using-javascript/
* @license http://www.opensource.org/licenses/bsd-license.php BSD License
*/
export default class PNGEncoder {
constructor(width, height, depth) {
this.width = width;
this.height = height;
this.depth = depth;
// pixel data and row filter identifier size
this.pix_size = height * (width + 1);
// deflate header, pix_size, block headers, adler32 checksum
this.data_size = 2 + this.pix_size + 5 * Math.floor((0xfffe + this.pix_size) / 0xffff) + 4;
// offsets and sizes of Png chunks
this.ihdr_offs = 0; // IHDR offset and size
this.ihdr_size = 4 + 4 + 13 + 4;
this.plte_offs = this.ihdr_offs + this.ihdr_size; // PLTE offset and size
this.plte_size = 4 + 4 + 3 * depth + 4;
this.trns_offs = this.plte_offs + this.plte_size; // tRNS offset and size
this.trns_size = 4 + 4 + depth + 4;
this.idat_offs = this.trns_offs + this.trns_size; // IDAT offset and size
this.idat_size = 4 + 4 + this.data_size + 4;
this.iend_offs = this.idat_offs + this.idat_size; // IEND offset and size
this.iend_size = 4 + 4 + 4;
this.buffer_size = this.iend_offs + this.iend_size; // total PNG size
this.buffer = [];
this.palette = {};
this.pindex = 0;
var _crc32 = [];
var i;
// initialize buffer with zero bytes
for (i = 0; i < this.buffer_size; i++) {
this.buffer[i] = "\x00";
}
// initialize non-zero elements
PNGEncoder._write(this.buffer, this.ihdr_offs, PNGEncoder._byte4(this.ihdr_size - 12), 'IHDR', PNGEncoder._byte4(width), PNGEncoder._byte4(height), "\x08\x03");
PNGEncoder._write(this.buffer, this.plte_offs, PNGEncoder._byte4(this.plte_size - 12), 'PLTE');
PNGEncoder._write(this.buffer, this.trns_offs, PNGEncoder._byte4(this.trns_size - 12), 'tRNS');
PNGEncoder._write(this.buffer, this.idat_offs, PNGEncoder._byte4(this.idat_size - 12), 'IDAT');
PNGEncoder._write(this.buffer, this.iend_offs, PNGEncoder._byte4(this.iend_size - 12), 'IEND');
// initialize deflate header
var header = ((8 + (7 << 4)) << 8) | (3 << 6);
header+= 31 - (header % 31);
PNGEncoder._write(this.buffer, this.idat_offs + 8, PNGEncoder._byte2(header));
// initialize deflate block headers
for (i = 0; (i << 16) - 1 < this.pix_size; i++) {
var size, bits;
if (i + 0xffff < this.pix_size) {
size = 0xffff;
bits = "\x00";
} else {
size = this.pix_size - (i << 16) - i;
bits = "\x01";
}
PNGEncoder._write(this.buffer, this.idat_offs + 8 + 2 + (i << 16) + (i << 2), bits, PNGEncoder._byte2lsb(size), PNGEncoder._byte2lsb(~size));
}
/* Create crc32 lookup table */
for (i = 0; i < 256; i++) {
var c = i;
for (var j = 0; j < 8; j++) {
if (c & 1) {
c = -306674912 ^ ((c >> 1) & 0x7fffffff);
} else {
c = (c >> 1) & 0x7fffffff;
}
}
_crc32[i] = c;
}
this._crc32 = _crc32;
}
static _write(buffer, offs) {
for (var i = 2; i < arguments.length; i++) {
for (var j = 0; j < arguments[i].length; j++) {
buffer[offs++] = arguments[i].charAt(j);
}
}
}
static _byte2(w) {
return String.fromCharCode((w >> 8) & 255, w & 255);
}
static _byte4(w) {
return String.fromCharCode((w >> 24) & 255, (w >> 16) & 255, (w >> 8) & 255, w & 255);
}
static _byte2lsb(w) {
return String.fromCharCode(w & 255, (w >> 8) & 255);
}
// compute the index into a png for a given pixel
index(x,y) {
var i = y * (this.width + 1) + x + 1;
var j = this.idat_offs + 8 + 2 + 5 * Math.floor((i / 0xffff) + 1) + i;
return j;
}
// convert a color and build up the palette
color(red, green, blue, alpha) {
alpha = alpha >= 0 ? alpha : 255;
var color = (((((alpha << 8) | red) << 8) | green) << 8) | blue;
if (typeof this.palette[color] == "undefined") {
if (this.pindex == this.depth) return "\x00";
var ndx = this.plte_offs + 8 + 3 * this.pindex;
this.buffer[ndx + 0] = String.fromCharCode(red);
this.buffer[ndx + 1] = String.fromCharCode(green);
this.buffer[ndx + 2] = String.fromCharCode(blue);
this.buffer[this.trns_offs+8+this.pindex] = String.fromCharCode(alpha);
this.palette[color] = String.fromCharCode(this.pindex++);
// console.log("Added colour [" + red + "," + green + "," + blue +
// "], palette now has " + this.pindex + " colour(s)");
}
return this.palette[color];
}
// output a PNG string, Base64 encoded
getBase64() {
var s = this.getDump();
// If the current browser supports the Base64 encoding
// function, then offload the that to the browser as it
// will be done in native code.
if ((typeof window.btoa !== 'undefined') && (window.btoa !== null)) {
return window.btoa(s);
}
var ch = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
var c1, c2, c3, e1, e2, e3, e4;
var l = s.length;
var i = 0;
var r = "";
do {
c1 = s.charCodeAt(i);
e1 = c1 >> 2;
c2 = s.charCodeAt(i+1);
e2 = ((c1 & 3) << 4) | (c2 >> 4);
c3 = s.charCodeAt(i+2);
if (l < i+2) { e3 = 64; } else { e3 = ((c2 & 0xf) << 2) | (c3 >> 6); }
if (l < i+3) { e4 = 64; } else { e4 = c3 & 0x3f; }
r+= ch.charAt(e1) + ch.charAt(e2) + ch.charAt(e3) + ch.charAt(e4);
} while ((i+= 3) < l);
return r;
}
// output a PNG string
getDump() {
// compute adler32 of output pixels + row filter bytes
var BASE = 65521; /* largest prime smaller than 65536 */
var NMAX = 5552; /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
var s1 = 1;
var s2 = 0;
var n = NMAX;
for (var y = 0; y < this.height; y++) {
for (var x = -1; x < this.width; x++) {
s1+= this.buffer[this.index(x, y)].charCodeAt(0);
s2+= s1;
if ((n-= 1) === 0) {
s1%= BASE;
s2%= BASE;
n = NMAX;
}
}
}
s1%= BASE;
s2%= BASE;
PNGEncoder._write(this.buffer, this.idat_offs + this.idat_size - 8, PNGEncoder._byte4((s2 << 16) | s1));
// compute crc32 of the PNG chunks
function crc32(png, offs, size, crctable) {
var crc = -1;
for (var i = 4; i < size-4; i += 1) {
crc = crctable[(crc ^ png[offs+i].charCodeAt(0)) & 0xff] ^ ((crc >> 8) & 0x00ffffff);
}
PNGEncoder._write(png, offs+size-4, PNGEncoder._byte4(crc ^ -1));
}
crc32(this.buffer, this.ihdr_offs, this.ihdr_size, this._crc32);
crc32(this.buffer, this.plte_offs, this.plte_size, this._crc32);
crc32(this.buffer, this.trns_offs, this.trns_size, this._crc32);
crc32(this.buffer, this.idat_offs, this.idat_size, this._crc32);
crc32(this.buffer, this.iend_offs, this.iend_size, this._crc32);
// convert PNG to string
return "\x89PNG\r\n\x1a\n"+this.buffer.join('');
}
}
