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Re: [Rendering order] z-depth and 3D effects

From: Jonathan Watt <jwatt@jwatt.org>
Date: Mon, 16 Nov 2009 18:33:04 +0100
Message-ID: <4B018CD0.3050701@jwatt.org>
To: Steve Withall <steve@withallyourequire.com>
CC: www-svg@w3.org
Hi Steve,

Have you looked at the alternative z-index proposal that I made:


It practice it's similar to the "SVG Rendering Order" proposal you refer to, but
more general. Rather than just being able to position sibling elements relative
to each other in the z-axis, you can position elements relative to other
elements in entire element trees.

If this doesn't meet your needs, I'd be very interested to hear about it. A
small concrete example (with code) would also be very useful in that case.


On 2009-11-11 1:56 AM, Steve Withall wrote:
> Esteemed experts,
> The recent draft "SVG Rendering Order" specification makes a few 3D 
> effects easier to achieve. So does the draft "Transforms" 
> specification. They add to what can be done using filters (drop 
> shadows and lighting, in particular). But all these effects are 
> independent of one another. There's no underlying 3D model, so it is 
> possible merely to *contrive* to make individual objects appear 3D.
> Of course SVG is a format for 2D graphics, and should stay that way. 
> For your consideration I suggest that a 3D model sufficient for SVG 
> could be achieved by allowing a *z-depth* to be defined for each 
> element: its distance above (or below) a datum plane. (I avoid 
> calling it z-height because heights in SVG mean the y dimension.) 
> This single value would be a sufficient basis for calculating 
> consistent drop shadows and consistent perspective transforms across 
> many or all elements.
> Alternatively a z-depth could be defined for each z-order value. 
> That's probably sufficient in some situations, but not in others.
> An additional use case I have is displaying multiple SVG canvases 
> layered one above the other. I want each *canvas* to have a z-depth, 
> so I can throw well-positioned drop shadows from objects in one 
> canvas on to objects in canvases below. This can be regarded as the 
> ability to define the "absolute" (wider world) z-depth of the datum 
> plane for each canvas.
> Finally, is it worth the Working Group making a formal statement of 
> the extent and limits of SVG's 3D ambitions? (Forgive me if this 
> exists somewhere that I don't know about.) It could be something 
> along the lines of treating each element as two dimensional, but 
> offering ways to make collections of these 2D elements appear as if 
> they exist in a 3D environment.
> Thanks, Steve.
Received on Monday, 16 November 2009 17:34:11 UTC

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