[whatwg] Canvas toDataURL and device dpi resolution

John Knottenbelt jknotten at chromium.org
Fri Dec 2 03:49:56 PST 2011

Thanks for your advice. I have submitted :-
 - https://www.w3.org/Bugs/Public/show_bug.cgi?id=15041 to request the
spec be clarified in this regard.
 - https://www.w3.org/Bugs/Public/show_bug.cgi?id=15042 to request the
test to be updated to cope with higher resolution backing stores.

Should I cc anyone on these bugs?


On Thu, Dec 1, 2011 at 7:44 PM, Edward O'Connor <eoconnor at apple.com> wrote:
> John Knottenbelt wrote:
>> How should the data url returned by toDataURL be sized in the case of
>> a high device dpi resolution system? E.g. where the canvas's backing
>> store horizontal and vertical dimensions are some multiple of the
>> specified width and height in CSS pixels.
> In the case of getImageData(), the spec says:
> "[T]he data returned by getImageData() is at the resolution of the
> canvas backing store. This is likely to not be one device pixel to each
> CSS pixel if the display used is a high resolution display."
> http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#pixel-manipulation
> I would expect toDataURL() to use the same underlying machinery as
> getImageData() behind the scenes. This should definitely be clarified in
> the spec.
>> Is this correct behaviour, or is the test correct and I simply have a
>> bug in WebKit?
> I believe WebKit behaves correctly in this case.
> Ted

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