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

Kenneth Russell kbr at google.com
Mon Mar 11 16:28:36 PDT 2013

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:

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

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




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