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Re: SVG 1.2 10 Alternate content based on display resolutions

From: Dean Jackson <dean@w3.org>
Date: Wed, 4 Jun 2003 13:15:27 +1000
To: Jim Ley <jim@jibbering.com>
Cc: www-svg@w3.org
Message-ID: <20030604031527.GC10057@grorg.org>

On Fri, 09 May 2003, Jim Ley wrote:

> I think in general the Alternate content section could be simply extended to
> cope with low bandwidth aswell as different display resolutions - it may
> also be possible to extend it in such a way that you can specify different
> images for different sub-regions for when zooming in/out without forcing the
> download of a complete more accurate map and the bandwidth costs of that.
> (basically doing what we do in Level-of-Detail script changing situations)

I like the idea.

> Exactly how that extension might be managed I'm not sure...  For the
> bandwidth case, a simple advisory content-size attribute on the subImage
> element would provide a hint to the UA, which it could then use in the
> decision making process.

But we'd probably have to specify the behaviour. Can you make
any suggestions? (ie. what algorithm is the UA using).

> For the more complicated LOD regional part, then the subImage elements could
> also have x/y/w/h  attributes defining the region of the parent Image
> element that they refer to, looking something like this:
> <image x="200" y="200" width="100px" height="100px"
>          min-pixel-size="1" max-pixel-size="1"
>          xlink:href="myimage.png">
>     <subImage xlink:href="myimage-lg.png"
>               min-pixel-size=".5" max-pixel-size=".5"
>               x="25px" y="25px" height="50px" width="50px">
>        <desc>An alternative image for the central portion of the parent
> Image</desc>
>     </subImage>
> </image>
> The UA can then choose to switch to the subIamge if the zoomed region would
> be better served by it.  This would give us Level-of-detail functionality
> without needing scripting.

Nice suggestion. Thomas, who originally proposed this feature, had implemented
something like this with nested SVG images (which included nested SVG images, etc).

> What would happen in situations where the zoom overlaps regions which don't
> have a subImage is something else I don't know about, rendering both images
> would be possible, or you could just use the parent one.

I'd prefer it to show both, since I don't want a 1-pixel pan to radically
change the display.

Received on Tuesday, 3 June 2003 23:15:33 UTC

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