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/options.tsx

@@ -0,0 +1,39 @@
+import { h, Component } from 'preact';
+import { bind, inputFieldValueAsNumber } from '../../lib/util';
+import { EncodeOptions } from './encoder';
+
+type Props = {
+  options: EncodeOptions;
+  onChange(newOptions: EncodeOptions): void;
+};
+
+export default class OptiPNGEncoderOptions extends Component<Props, {}> {
+  @bind
+  onChange(event: Event) {
+    const form = (event.currentTarget as HTMLInputElement).closest('form') as HTMLFormElement;
+
+    const options: EncodeOptions = {
+      level: inputFieldValueAsNumber(form.level),
+    };
+    this.props.onChange(options);
+  }
+
+  render({ options }: Props) {
+    return (
+      <form>
+        <label>
+          Effort:
+          <input
+            name="level"
+            type="range"
+            min="0"
+            max="7"
+            step="1"
+            value={'' + options.level}
+            onChange={this.onChange}
+          />
+        </label>
+      </form>
+    );
+  }
+}