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

Hi, Steve-

Thanks for the additional use cases.  We know we will have to reconcile 
any concept of z-index with 2.5D transformations and occlusion, and I'm 
not sure we quite have that covered yet.

Jonathan Watt has volunteered to take on formalizing the z-index topic, 
along with its ramifications with the rendering model, and to expand the 
proposal he made earlier.  Anthony Grasso will be handling the new 
transformation stuff, in conjunction with the CSS transformations.

You're right that we should clarify where we intend to go with this... 
we certainly don't intend to make SVG a true 3D language, and we will 
try to produce a coherent primer or set of examples for common pseudo-3D 
effects that will clarify it to authors (and implementers).

Regards-
-Doug Schepers
W3C Team Contact, SVG and WebApps WGs

Steve Withall wrote (on 11/10/09 7:56 PM):
> 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 Sunday, 15 November 2009 10:30:47 UTC