Two workers & worker termination (#198)

* Refactoring codecs

* Plugging in new processor

* Fixing decorator

* MozJPEG free issue

* Better worker aborting, and terminate workers that aren't used for 10 seconds

* Better comment

* Ooops, half-typed comment

* Uncommenting problematic line

* Surma fixed it!

* Abstracting WASM initialisation

* Better comment

* Don't need this.

* Adding ticket

* noInitalRun

* Reverting MozJPEG issue demo

* Making a const for worker timeout

* Inline docs

* Bail early rather than nesting

* Addressing nits

src/codecs/resize/processor.ts

@@ -0,0 +1,49 @@
+import { nativeResize, NativeResizeMethod, drawableToImageData } from '../../lib/util';
+import { BitmapResizeOptions, VectorResizeOptions } from './processor-meta';
+
+function getCoverOffsets(sw: number, sh: number, dw: number, dh: number) {
+  const currentAspect = sw / sh;
+  const endAspect = dw / dh;
+
+  if (endAspect > currentAspect) {
+    const newSh = sw / endAspect;
+    const newSy = (sh - newSh) / 2;
+    return { sw, sh: newSh, sx: 0, sy: newSy };
+  }
+
+  const newSw = sh * endAspect;
+  const newSx = (sw - newSw) / 2;
+  return { sh, sw: newSw, sx: newSx, sy: 0 };
+}
+
+export function resize(data: ImageData, opts: BitmapResizeOptions): ImageData {
+  let sx = 0;
+  let sy = 0;
+  let sw = data.width;
+  let sh = data.height;
+
+  if (opts.fitMethod === 'cover') {
+    ({ sx, sy, sw, sh } = getCoverOffsets(sw, sh, opts.width, opts.height));
+  }
+
+  return nativeResize(
+    data, sx, sy, sw, sh, opts.width, opts.height,
+    opts.method.slice('browser-'.length) as NativeResizeMethod,
+  );
+}
+
+export function vectorResize(data: HTMLImageElement, opts: VectorResizeOptions): ImageData {
+  let sx = 0;
+  let sy = 0;
+  let sw = data.width;
+  let sh = data.height;
+
+  if (opts.fitMethod === 'cover') {
+    ({ sx, sy, sw, sh } = getCoverOffsets(sw, sh, opts.width, opts.height));
+  }
+
+  return drawableToImageData(data, {
+    sx, sy, sw, sh,
+    width: opts.width, height: opts.height,
+  });
+}