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SVG 1.2 10 Alternate content based on display resolutions

From: Jim Ley <jim@jibbering.com>
Date: Fri, 9 May 2003 08:34:29 -0000
To: www-svg@w3.org
Message-ID: <b9g2te$er0$7@main.gmane.org>

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)

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.

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.

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.

Jim.
Received on Friday, 9 May 2003 08:40:50 GMT

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