[whatwg] Proposal: ImageData constructor or factory method with preexisting data

Ian Hickson ian at hixie.ch
Fri Aug 9 14:34:35 PDT 2013

On Fri, 9 Aug 2013, Rik Cabanier wrote:
> On Fri, Aug 9, 2013 at 1:32 PM, Ian Hickson <ian at hixie.ch> wrote:
> > On Mon, 11 Mar 2013, Kenneth Russell wrote:
> > >
> > > It would be useful to be able to create an ImageData [1] object with 
> > > preexisting data. The main use case is to display arbitrary data in 
> > > the 2D canvas context with no data copies.
> >
> > Doesn't ImageBitmap support this already? I'm not sure I understand 
> > the use case here. Where are you getting the image data from, that 
> > it's already in raw RGBA form rather than compressed e.g. as a PNG? 
> > (Presumably this isn't coming over the network, since I would imagine 
> > the time to compress and decompress an image is far smaller than the 
> > time to send uncompressed data. But maybe I'm wrong about that.)
> From re-reading the thread, it seems that this data comes from the 
> server (or a web worker?) as uncompressed data. The http protocol likely 
> did compression on the packets so the size difference is probably not 
> that great.
> I think the use-case is to avoid having to copy over the data pixel by 
> pixel from the arraybuffer.

Could you elaborate on the use case?

I'm happy to believe that there are times that a server or worker is 
generating lots of pixel data, but having never run into such a case 
myself, I would very much like to understand it better. It may be that 
there are better solutions to the real underlying problem.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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