Re: [whatwg] Canvas toDataURL and device dpi resolution
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? John On Thu, Dec 1, 2011 at 7:44 PM, Edward O'Connor 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 >
Re: [whatwg] Canvas toDataURL and device dpi resolution
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
[whatwg] Canvas toDataURL and device dpi resolution
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. The test http://philip.html5.org/tests/canvas/suite/tests/toDataURL.png.primarycolours.html makes a drawing with canvas, saves this drawing to a data url, loads the data url into an Image element and then draws that back to the canvas, and then performs some assertions that the image is as expected. I've been trying this out in the DumpRenderTree test runner of WebKit, where toDataURL returns an image derived from the canvas' backing store image data. If I set the device dpi scale to 2.0 to imitate a high DPI display, the test will fail because the image returned by toDataURL is now four times as big as the test expects it to be. Is this correct behaviour, or is the test correct and I simply have a bug in WebKit? Many thanks John
