[bartread]

Yeah, exactly that, although sadly Firefox represents a minority of traffic for me so OffscreenCanvas isn't a realistic option.

To your point about direct manipulation, I think you may be right. I'm talking about drawing rather than image processing, and no way I want to effectively re-implement a bunch of Canvas2D primitives, but what I could do is draw the image once on the foreground thread, extract the raw bytes, and then rotate those using image processing into a bunch of target arrays in the background. I'd then pass those arrays back to the foreground and create a set of corresponding images.

The only issue here, and I'd need to benchmark this, is that it's not clear to me how much of the time is spent drawing versus actually creating the images. If creating images is expensive this might not yield much of a gain.

The upshot is that this starts to sound like quite a bit of work when, what I could do, and which would be much simpler, is reduce the fidelity slightly: e.g., by rendering only 180 or 120 images, and tweaking the minimum angular velocity appropriately to avoid jerky animation.

And then I suppose I'm back to the point that somebody else made, which is that Web Workers may not be that useful in the real world. :/