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

[Rik Cabanier]

On Tue, Mar 12, 2013 at 11:40 AM, Kenneth Russell <kbr at google.com> wrote:

> On Tue, Mar 12, 2013 at 11:15 AM, Rik Cabanier <cabanier at gmail.com> wrote:
> > sounds good!
> > I think this is a convenient and useful addition.
>
> Great.
>
> > do you want to keep doubles to define the dimensions instead of
> integers? If
> > so, the size should probably  4 * ceil(sw) * ceil(sh)
>
> I would prefer to use integers, and only used doubles to be consistent
> with the other APIs like getImageData and createImageData. In this
> case it would make more sense to use integers, since the width and
> height are simply being used to interpret preexisting data in the
> Uint8ClampedArray.


The current canvas spec doesn't specifically state what happens with
partial pixels. What happens today?
(Also is there a definition somewhere that states when a pixel is
considered filled?)

> I don't think it is necessary to provide a createImageDataHD in this
> interface. The caller will know the devicePixelRatio and determine
> whether to generate high-DPI data.

That probably won't work since it results in code that executes differently
on devices that are HD.


>
> > On Tue, Mar 12, 2013 at 10:50 AM, Kenneth Russell <kbr at google.com>
> wrote:
> >>
> >> It should simply reference the Uint8ClampedArray, not copy it or do
> >> anything else esoteric. The only way to display an ImageData in the 2D
> >> canvas context is via the putImageData API. I am not proposing
> >> changing those semantics.
> >>
> >> -Ken
> >>
> >>
> >>
> >> On Mon, Mar 11, 2013 at 5:00 PM, Rik Cabanier <cabanier at gmail.com>
> wrote:
> >> > Do you expect that createImageData creates an internal copy of the
> >> > Uint8ClampedArray object or is it live?
> >> >
> >> >
> >> > On Mon, Mar 11, 2013 at 4:28 PM, Kenneth Russell <kbr at google.com>
> 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.
> >> >>
> >> >> Proposed IDL:
> >> >>
> >> >> [NoInterfaceObject]
> >> >> interface ImageDataFactories {
> >> >>   ImageData createImageData(Uint8ClampedArray data, double sw, double
> >> >> sh);
> >> >> };
> >> >> Window implements ImageDataFactories;
> >> >> WorkerGlobalScope implements ImageDataFactories;
> >> >>
> >> >> createImageData would throw an exception if the length of the
> >> >> Uint8ClampedArray was not equal to 4 * floor(sw) * floor(sh), or at
> >> >> least, if the length of the array was less than this value. (Similar
> >> >> wording would be used to that of CanvasRenderingContext2D's
> >> >> createImageData.)
> >> >>
> >> >> I don't think it is necessary to provide a createImageDataHD in this
> >> >> interface. The caller will know the devicePixelRatio and determine
> >> >> whether to generate high-DPI data.
> >> >>
> >> >> [1]
> >> >>
> >> >>
> http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#imagedata
> >> >>
> >> >> Comments?
> >> >>
> >> >> Thanks,
> >> >>
> >> >> -Ken
> >> >
> >> >
> >
> >
>