Re: [css3-images] Features Overview

On Sat, May 7, 2011 at 8:48 AM, fantasai <fantasai.lists@inkedblade.net> wrote:
> On 05/06/2011 11:41 AM, Brian Manthos wrote:
>>
>>>> background-image: url('sprites.png#xywh=10,30,60,20');
>>
>> Interesting.
>>
>> How does this behave for formats that contain multiple source resolutions
>> within the same file?
>>
>>        background-image:
>> url("http://www.microsoft.com/favicon.ico#xywh=10,30,60,20");
>
> Hm, that's a good question. If we look at the sizing algorithm,
>  http://dev.w3.org/csswg/css3-images/#sizing
> it says to use the largest size when determining the intrinsic dimensions
> if there are multiple sizes. So we'd use that, and then clip out the
> piece represented by the fragment identifier to get the intrinsic size.
>
> The CSS⇋Object negotiation algorithm says you use the intrinsic size as
> an input into the sizing algorithm to compute a "concrete object size".
>
> Once you have a concrete object size, then you go back to the image
> and tell it to paint itself into this rectangle. How it negotiates a
> mismatch between itself and the "viewport" it's given isn't defined
> by CSS. (It's out-of-scope, since different formats behave differently
> when confronted by such a mismatch.) I assume in the normal case (no
> fragment), a .ico file will choose the source resolution that best
> matches the size it's given. If the fragment is given in percentages,
> that still makes sense here. But if it's given in pixels, all the
> fragments will be the same size...
>
> Probably what you /want/ to do is translate the pixel sizes to percents
> based on the source resolution that was chosen in the intrinsic sizing
> step, then choose the one that gives you the best match, just like you
> would for the whole image.
>
> Does that make sense?
>
> (On a related note, the Media Fragments WG needs to specify what happens
> when the fragment identifies coordinates that are not within the image
> bounds.)

Error handling is indeed what we are extensively working on right now. :-)

Cheers,
Silvia.

Received on Friday, 6 May 2011 22:57:33 UTC