skia2/modules/canvaskit/future_apis/ImageDecoder.md

ImageDecoder API

Date Updated: June 16, 2020

Summary and Links

The ImageDecoder API handles decoding of both still and animated images. Similar to the larger web codecs proposal which is focused more on video and audio. The ImageDecoder API could be used with CanvasKit.MakeImageFromCanvasImageSource for creating CanvasKit compatible SkImages. For still images, the createImageBitmap(blob) API achieves the same result.

• Explainer
• Prototype
• Discourse

Currently available as a prototype behind the --enable-blink-features=WebCodecs flag in Chrome Canary, works in version 85.0.4175.0.

Running the prototype

1. Download and install Chrome Canary. Verify that you have version 85.0.4175.0 or later.
2. Close ALL open instances of chromium browsers, including chrome.
3. Run Chrome Canary with the --enable-blink-features=WebCodecs flag.

MacOS: Run /applications/Google\ Chrome\ Canary.app/Contents/MacOS/Google\ Chrome\ Canary --enable-blink-features=WebCodecs

Windows, Linux: https://www.chromium.org/developers/how-tos/run-chromium-with-flags

3. Navigate to: http://storage.googleapis.com/dalecurtis/test-gif.html?src=giphy.gif
4. You should see a cute animated cat illustration.

Example API Usage with CanvasKit

With a still image:

const response = await fetch(stillImageUrl); // e.g. png or jpeg
const data = await response.arrayBuffer();

const imageDecoder = new ImageDecoder({ data });
const imageBitmap = await imageDecoder.decode();

const skImage = CanvasKit.MakeImageFromCanvasImageSource(imageBitmap);
// do something with skImage, such as drawing it

With an animated image:

const response = await fetch(animatedImageUrl); // e.g. gif or mjpeg
const data = await response.arrayBuffer();

const imageDecoder = new ImageDecoder({ data });

for (let frame = 0; frame < imageDecoder.frameCount; frame++) {
    const imageBitmap = await imageDecoder.decode(frame);
    const skImage = CanvasKit.MakeImageFromCanvasImageSource(imageBitmap);
    // do something with skImage, such as drawing it
}