[whatwg] Processing the zoom level - MS extensions to window.screen

Charles Pritchard chuck at jumis.com
Sun Nov 21 17:36:49 PST 2010

On 11/21/10 4:56 PM, Robert O'Callahan wrote:
> On Mon, Nov 22, 2010 at 1:40 PM, Charles Pritchard <chuck at jumis.com 
> <mailto:chuck at jumis.com>> wrote:
>     I would point out that the MS proposal has an independent X and Y
>     scaling mechanism.
> Does anyone know of any modern displays which have different X and Y 
> resolution?
I've seen more than one LCD-style wide-screen TV which does, but it's 
not so modern anymore.
Beats me. Perhaps MS can chime in with some use cases, as they have 
broad experience with alternative
displays. I doubt this is a mainstream issue, but it may still be an issue.
>     I believe that dpi ratio is simply set to "2" (or .5... sorry a
>     bit rusty) on the iOS 4 retina display.
> There will be cases where zooming doesn't change device-pixel-ratio. 
> Mobile browsers tend to have a "fast" zoom out which doesn't change 
> the layout (mostly), and that might not change device-pixel-ratio. I 
> think that's OK for your use cases as long as device-pixel-ratio 
> reports the ratio as if the page is "zoomed in".
I'll review the current use of dpi ratio in Firefox 4 and get back to 
the list on it.

At the very least, I'd like to make sure the proper routines are 
specified in the specs.
"zoom" does trigger a layout change, and a "resize" event. And that's 
fine. If it's not specifically stated in the specs, I'd like it to be.

Following that, we do need a reliable way to grab screen metrics. If dpi 
ratio is reliable, I'm happy to use it.

My concern is that existing implementations of DPI have broken the 
variable for "zoom" uses.
I do realize that other people screwing up their implementation of the 
standard doesn't mean we should have to change the standard.

At the very least, it means we should update the standard to more 
explicitly define its behavior.

I'm eager to get this functionality met, as legible zoom is very 
important to me, and the current
collection of browsers is completely fragmented in its 

Thanks for working with me on it.

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