[webkit-dev] Canvas backing resolution

Charles Pritchard chuck at jumis.com
Fri Mar 4 10:08:52 PST 2011

In the future?

On Mar 4, 2011, at 8:51 AM, Oliver Hunt <oliver at apple.com> wrote:

> For reference desktop webkit implementations will automatically increase the canvas backing store resolution as the device:css pixel ratio increases.
> --Oliver
> On Mar 4, 2011, at 1:44 AM, Charles Pritchard wrote:
>> On 3/4/2011 1:35 AM, Kenneth Rohde Christiansen wrote:
>>> Hi again,
>>>> I'm trying to keep the canvas bitmap at the same pixel resolution as the
>>>> device,
>>>> otherwise it is blurry.
>>> OK, I see.
>>>> This, for example, works if the pixel ratio is 2.
>>>> <canvas style="width: 100px; height: 100px;" width="200"
>>>> height="200"></canvas>
>>>> Yes, when the user has a zoom level set, I'd like to paint to match the
>>>> pixel ratio,
>>>> so that, a zoomed in user still receives crisp output, instead of blurry
>>>> output.
>>> -webkit-device-pixel-ratio does not change when the user scaled the
>>> content; it is a device value.
>>> On old iPhone it is 1.0, on Android it can be 0.5, 1.0 and 1.5
>>> depending on it being a low, medium (160) or high dpi (240) device. On
>>> the iPhone 4 and the new iPod Touch it is 2.0.
>>> On Android devices, with for instance, a device-pixel-ratio of 1.5,
>>> you can disable the upscaling by adding target-densitydpi=device-dpi
>>> to the viewport meta tag.
>>> What you can do is to disable user scaling (add user-scaling=no to the
>>> viewport meta tag) and then handle zooming in your app using the touch
>>> events. This only works on mobile devices though.
>> I haven't debugged with enough tablet devices, such as the color kindle, to know how many webkit distros it works with.
>> What should I do about user zoom on the desktop (and possibly, the kindle) ?
>> Drawing in high res, just-in-case, makes for a poorer experience for users at a 1.0 ratio,
>> and asking users to slide a "sharpen" slider is a little awkward.
>> Mozilla, in their implementation, has setup device-pixel-ratio to scale when the user scales content;
>> they directly expose window css pixel ratio value to trusted scripts, but not to web content; requiring
>> web content to use css device-pixel-ratio.
>> Microsoft has exposed the values through window.screen.
>> -Charles
>> _______________________________________________
>> webkit-dev mailing list
>> webkit-dev at lists.webkit.org
>> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev

More information about the webkit-dev mailing list