OffscreenCanvas support?

[mmocny]

Is there any plan to support OffscrenCanvas with these new apis?

My read is that the element being placed has to be a "direct child of the canvas element". I think this does limit the api to the main thread, since you cannot pass a reference to an element across to workers, and the OffscreenCanvas, although transferable, is not an element that would have access to the actual <canvas> children.

Is that correct?

---

I think it would be interesting to support some sort of (even limited) use case for Web workers, such as just supplying dynamic data for an html template / Web Component / DOM Parts, etc.

One of the uses cases I have could be summarized as:

• I have a web component that supplies UI. It could be instantiated on the main thread and attached to the canvas as a child.
• This component is completely isolated from the rest of the page, can be in a shadow root.
• Component adjusts itself visually based on custom props passed to it.
• The values of these props are dynamically computed and updated by a web worker.
• All the features the component needs are already supported by web workers-- except for the ability to render a DOM element.

Besides just moving the cost of the compute for props off the main thread, a requirement is to asynchronously display visual updates decoupled from the main thread animation frame rate. So just a convenience wrapper around postMessage is not sufficient for this use case.

Is it viable to consider something like this in the future? Or does it fundamentally require main thread?

Cheers.

---

(Apologies, I know I asked this question elsewhere but am failing to find the source now...)

[schenney-chromium]

I think you asked the question on the original proposal doc that was circulating.

Anyways, the issue is running style/layout/paint on the worker to determine the display list for the element. I suppose you could somehow pass that display list to the worker, but for the worker to do anything other than just draw it you would need a whole new parameterized display list concept (I think).