[whatwg] More random comments on the putImageData definition
Oliver Hunt
oliver at apple.com
Fri Jan 25 15:05:19 PST 2008
Ah true I had forgotten that, however this still fails for non-
integral ratios :-/
--Oliver
On Jan 25, 2008, at 3:05 PM, Anne van Kesteren wrote:
> On Fri, 25 Jan 2008 23:57:56 +0100, Oliver Hunt <oliver at apple.com>
> wrote:
>> Another thing that we need is some way to determine what the device
>> pixel->css pixel ratio is. Currently there's isn't even a real way
>> to tell that it's 1:1 -- you would have do do a fillRect(width-1,
>> height-1, 1, 1),; then getImageData(width-1, height-1, 1, 1) and
>> see if they match. Conceivably you could do this multiple times to
>> estimate the ratio, but it would be non-trivial.
>
> You can determine this by checking the height and width attributes
> on the ImageData object. If you get a 2x2 region and ImageData.width
> and .height return 4 you know there's a factor two scaling happening
> between canvas pixels and device pixels. What the factor is between
> canvas pixels and CSS pixels isn't really relevant (and easy to
> determine).
>
>
> --
> Anne van Kesteren
> <http://annevankesteren.nl/>
> <http://www.opera.com/>
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