fast-png
Version:
PNG image decoder and encoder written entirely in JavaScript
148 lines • 4.89 kB
JavaScript
import { IOBuffer } from 'iobuffer';
import { deflate } from 'pako';
import { writeCrc } from './helpers/crc';
import { writeSignature } from './helpers/signature';
import { encodetEXt } from './helpers/text';
import { ColorType, CompressionMethod, FilterMethod, InterlaceMethod, } from './internalTypes';
const defaultZlibOptions = {
level: 3,
};
export default class PngEncoder extends IOBuffer {
_png;
_zlibOptions;
_colorType;
constructor(data, options = {}) {
super();
this._colorType = ColorType.UNKNOWN;
this._zlibOptions = { ...defaultZlibOptions, ...options.zlib };
this._png = this._checkData(data);
this.setBigEndian();
}
encode() {
writeSignature(this);
this.encodeIHDR();
this.encodeData();
if (this._png.text) {
for (const [keyword, text] of Object.entries(this._png.text)) {
encodetEXt(this, keyword, text);
}
}
this.encodeIEND();
return this.toArray();
}
// https://www.w3.org/TR/PNG/#11IHDR
encodeIHDR() {
this.writeUint32(13);
this.writeChars('IHDR');
this.writeUint32(this._png.width);
this.writeUint32(this._png.height);
this.writeByte(this._png.depth);
this.writeByte(this._colorType);
this.writeByte(CompressionMethod.DEFLATE);
this.writeByte(FilterMethod.ADAPTIVE);
this.writeByte(InterlaceMethod.NO_INTERLACE);
writeCrc(this, 17);
}
// https://www.w3.org/TR/PNG/#11IEND
encodeIEND() {
this.writeUint32(0);
this.writeChars('IEND');
writeCrc(this, 4);
}
// https://www.w3.org/TR/PNG/#11IDAT
encodeIDAT(data) {
this.writeUint32(data.length);
this.writeChars('IDAT');
this.writeBytes(data);
writeCrc(this, data.length + 4);
}
encodeData() {
const { width, height, channels, depth, data } = this._png;
const slotsPerLine = channels * width;
const newData = new IOBuffer().setBigEndian();
let offset = 0;
for (let i = 0; i < height; i++) {
newData.writeByte(0); // no filter
/* istanbul ignore else */
if (depth === 8) {
offset = writeDataBytes(data, newData, slotsPerLine, offset);
}
else if (depth === 16) {
offset = writeDataUint16(data, newData, slotsPerLine, offset);
}
else {
throw new Error('unreachable');
}
}
const buffer = newData.toArray();
const compressed = deflate(buffer, this._zlibOptions);
this.encodeIDAT(compressed);
}
_checkData(data) {
const { colorType, channels, depth } = getColorType(data);
const png = {
width: checkInteger(data.width, 'width'),
height: checkInteger(data.height, 'height'),
channels,
data: data.data,
depth,
text: data.text,
};
this._colorType = colorType;
const expectedSize = png.width * png.height * channels;
if (png.data.length !== expectedSize) {
throw new RangeError(`wrong data size. Found ${png.data.length}, expected ${expectedSize}`);
}
return png;
}
}
function checkInteger(value, name) {
if (Number.isInteger(value) && value > 0) {
return value;
}
throw new TypeError(`${name} must be a positive integer`);
}
function getColorType(data) {
const { channels = 4, depth = 8 } = data;
if (channels !== 4 && channels !== 3 && channels !== 2 && channels !== 1) {
throw new RangeError(`unsupported number of channels: ${channels}`);
}
if (depth !== 8 && depth !== 16) {
throw new RangeError(`unsupported bit depth: ${depth}`);
}
const returnValue = {
channels,
depth,
colorType: ColorType.UNKNOWN,
};
switch (channels) {
case 4:
returnValue.colorType = ColorType.TRUECOLOUR_ALPHA;
break;
case 3:
returnValue.colorType = ColorType.TRUECOLOUR;
break;
case 1:
returnValue.colorType = ColorType.GREYSCALE;
break;
case 2:
returnValue.colorType = ColorType.GREYSCALE_ALPHA;
break;
default:
throw new Error('unsupported number of channels');
}
return returnValue;
}
function writeDataBytes(data, newData, slotsPerLine, offset) {
for (let j = 0; j < slotsPerLine; j++) {
newData.writeByte(data[offset++]);
}
return offset;
}
function writeDataUint16(data, newData, slotsPerLine, offset) {
for (let j = 0; j < slotsPerLine; j++) {
newData.writeUint16(data[offset++]);
}
return offset;
}
//# sourceMappingURL=PngEncoder.js.map