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Re: SVG Compositing + 3D Transform

From: Robert O'Callahan <robert@ocallahan.org>
Date: Mon, 16 May 2011 22:03:16 +1200
Message-ID: <BANLkTi=sQJZMUA6LhEuaXM5y181MnfMNxA@mail.gmail.com>
To: Dirk Schulze <vbs85@gmx.de>
Cc: www-svg List <www-svg@w3.org>
On Mon, May 16, 2011 at 7:19 PM, Dirk Schulze <vbs85@gmx.de> wrote:

> I have a short question about combining the new specifications 3D Transform
> and Compositing (and maybe z-index as well). Isn't it possible that the
> source graphic could be placed behind the destination graphic with 3D
> Transforms? How would that influence the compositing of both graphics?

First of all, let me note that 'comp-op' applied to non-SVG content needs to
induce a CSS psuedo-stacking-context as 'opacity', 'filter' and other group
compositing operations do, to ensure that the element can be rendered as an
atomic unit (without having its parents interleaved with the parts of other
elements in z-order).

Then, your issue isn't a problem for z-index or 3D transforms without
preserve-3d. In those cases, elements and their parts can be rendered one by
one onto the destination canvas, in the order defined by CSS z-index. When
you need to render an element with 'comp-op', the contents of the background
are clearly defined and so is the result of the comp-op.

With preserve-3d though, there might be an issue, depending on whether depth
buffering is supposed to be used. I believe the spec there is still unclear.
If depth buffering is used then it's not clear what comp-op should do.

"Now the Bereans were of more noble character than the Thessalonians, for
they received the message with great eagerness and examined the Scriptures
every day to see if what Paul said was true." [Acts 17:11]
Received on Monday, 16 May 2011 10:03:47 UTC

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