Optipng (#156)

* omg it’s compiling

* example actually works

* Expose compression level options

* Disable crypto and path module emulation in webpack

* Update README

* Remove small image

* Use -O3 on optipng

* Free memory after copy

* Handle unexpected file reader return types

* Rename level label to effort

src/codecs/optipng/encoder.ts

@@ -0,0 +1,23 @@
+import { canvasEncode, blobToArrayBuffer } from '../../lib/util';
+import EncodeWorker from './Encoder.worker';
+
+export interface EncodeOptions {
+  level: number;
+}
+export interface EncoderState { type: typeof type; options: EncodeOptions; }
+
+export const type = 'png';
+export const label = 'OptiPNG';
+export const mimeType = 'image/png';
+export const extension = 'png';
+
+export const defaultOptions: EncodeOptions = {
+  level: 2,
+};
+
+export async function encode(data: ImageData, opts: EncodeOptions): Promise<ArrayBuffer> {
+  const pngBlob = await canvasEncode(data, mimeType);
+  const pngBuffer = await blobToArrayBuffer(pngBlob);
+  const encodeWorker = await new EncodeWorker();
+  return encodeWorker.compress(pngBuffer, opts);
+}