Merge pull request #194 from geotiffjs/web-images

Add support for WebP decompression via the browser

Author: constantinius

src/compression/index.js

@@ -26,3 +26,4 @@ addDecoder(7, () => import('./jpeg.js').then((m) => m.default));
 addDecoder([8, 32946], () => import('./deflate.js').then((m) => m.default));
 addDecoder(32773, () => import('./packbits.js').then((m) => m.default));
 addDecoder(34887, () => import('./lerc.js').then((m) => m.default));
+addDecoder(50001, () => import('./webimage.js').then((m) => m.default));

src/compression/webimage.js

@@ -0,0 +1,40 @@
+import BaseDecoder from './basedecoder.js';
+
+/**
+ * class WebImageDecoder
+ *
+ * This decoder uses the browsers image decoding facilities to read image
+ * formats like WebP when supported.
+ */
+export default class WebImageDecoder extends BaseDecoder {
+  constructor() {
+    super();
+    if (typeof createImageBitmap === 'undefined') {
+      throw new Error('Cannot decode WebImage as `createImageBitmap` is not available');
+    } else if (typeof document === 'undefined' && typeof OffscreenCanvas === 'undefined') {
+      throw new Error('Cannot decode WebImage as neither `document` nor `OffscreenCanvas` is not available');
+    }
+  }
+
+  async decode(fileDirectory, buffer) {
+    const blob = new Blob([buffer]);
+    const imageBitmap = await createImageBitmap(blob);
+
+    let canvas;
+    if (typeof document !== 'undefined') {
+      canvas = document.createElement('canvas');
+      canvas.width = imageBitmap.width;
+      canvas.height = imageBitmap.height;
+    } else {
+      canvas = new OffscreenCanvas(imageBitmap.width, imageBitmap.height);
+    }
+
+    const ctx = canvas.getContext('2d');
+    ctx.drawImage(imageBitmap, 0, 0);
+
+    // TODO: check how many samples per pixel we have, and return RGB/RGBA accordingly
+    // it seems like GDAL always encodes via RGBA which does not require a translation
+
+    return ctx.getImageData(0, 0, imageBitmap.width, imageBitmap.height).data.buffer;
+  }
+}