Define ImageBitmapSource in terms of CanvasImageSource

[annevk]

It seems CanvasImageSource is a subset.

Anyone happen to know why CanvasImageSource does not take Blob or ImageData?

[domenic]

@junov do you know why CanvasImageSource does not include Blob or ImageData?

[junov]

I don't know, but my guess would be lack demand and the existence of reasonable workarounds. Also the workarounds perform well. I kinda like the idea of not allowing drawImage(Blob,...). It encourages devs to go through ImageBitmap, which has better performance characteristics due to it's asynchronous mode of operation. On browsers that do not have ImageBitmap, you would use an intermediate <img>, which still has the advantage of providing internal caching that stores the resource in a form that is pre-decoded, pre-multiplied by alpha, pre-colorcorrected, and possibly cached on the GPU.

Similarly, if you want to do the equivalent of drawImage(ImageData, ...) with today's APIs, you would have to use an intermediate canvas, use putImageData on it, and do a canvas-to-canvas draw. The intermediate canvas allows the image data to be stored in a native internal format (e.g. pre-multiplied by alpha, possibly on the GPU), which will yield higher performance for repetitive draws of the same image data.

[annevk]

Yeah that makes sense. ImageBitmapSource is only used by an asynchronous API so it can have asynchronous sources.

I take it you have no objections to defining it in terms of CanvasImageSource plus these two types?

[junov]

Sure, that makes sense.

[annevk]

Hmm I just noticed CanvasImageSource also takes CanvasRenderingContext2D. Is that a leftover bug from when the constructor of that interface was removed?

[junov]

Oh yeah, that should not be there.

[annevk]

I'll try to clean that up.

[junov]

Thanks.