WorkerCanvas

WebIDL

[Constructor(unsigned long width, unsigned long height)]
interface WorkerCanvas {
  attribute unsigned long width;
  attribute unsigned long height;
  RenderingContext? getContext(DOMString contextId, any... arguments); 
  void toBlob(FileCallback? _callback, optional DOMString type, any... arguments);
  ImageBitmap transferToImageBitmap();
};

WorkerCanvas implements Transferable;
ImageBitmap implements Transferable;

partial interface HTMLCanvasElement {
  WorkerCanvas transferControlToWorker();
};

partial interface ImageBitmap {
  void transferToImage(HTMLImageElement image);
};

Spec changes

Transferring of ImageBitmaps has to be defined. It should neuter the ImageBitmap in the sending thread. Neutering sets the ImageBitmap's width and height to 0.

HTMLCanvasElement.transferControlToWorker behaves like transferControlToProxy in the current WHATWG spec. WorkerCanvas is Transferable, but transfer fails if transferred other than from the main thread to a worker. All its methods throw if not called on a worker, or if it's neutered.

ImageBitmap.transferToImage removes the image element's "src" attribute and makes the image display the contents of the ImageBitmap (until the next transferToImage to that image, or until the image's "src" attribute is set). The ImageBitmap is neutered.