Re: [css-compositing] new Editor's draft posted -> update

On Fri, May 24, 2013 at 11:09 AM, Rik Cabanier <> wrote:

> I think there is now a clear path on how to calculate the backdrop for HTML

Well, maybe.

Currently the spec says
"However certain operations that cause the creation of stacking context
(such as 3D transforms or a non-default blend mode) [CSS21] will cause a
group to be isolated. This behavior is described in more detail in Isolated
Gropus." [sic]
However, nothing in the spec describes exactly what induces an "isolated

Also, I think every isolated group needs to be a stacking context since we
can't allow two elements in an isolated group to have other content not in
the group inserted between them in z-order. So every element that's an
isolated group would have to be a stacking context, and every element
that's a stacking context would have to be an isolated group, so they're
almost exactly the same thing. Except that SVG images rendered in CSS or
via <img> are also isolated groups.

If we do that, I think we can probably implement this in our compositor.
For every element that requires non-standard blending with the background,
we'd find the nearest ancestor stacking context, which induces an isolated
group on that element. We'd tell the compositor about those isolated
groups, and it would then be able to compute the backdrops for blended
elements within these groups. Needs more thought though.

If that works, I think we should make the CSS/SVG filters "BackgroundImage"
value be evaluated the same way and dispense with "enable-background".
Also, it fits better with our priorities to experiment with this as part of
CSS/SVG filters instead of implementing CSS blending and compositing right

q“qIqfq qyqoquq qlqoqvqeq qtqhqoqsqeq qwqhqoq qlqoqvqeq qyqoquq,q qwqhqaqtq
qcqrqeqdqiqtq qiqsq qtqhqaqtq qtqoq qyqoquq?q qEqvqeqnq qsqiqnqnqeqrqsq
qlqoqvqeq qtqhqoqsqeq qwqhqoq qlqoqvqeq qtqhqeqmq.q qAqnqdq qiqfq qyqoquq
qdqoq qgqoqoqdq qtqoq qtqhqoqsqeq qwqhqoq qaqrqeq qgqoqoqdq qtqoq qyqoquq,q
qwqhqaqtq qcqrqeqdqiqtq qiqsq qtqhqaqtq qtqoq qyqoquq?q qEqvqeqnq
qsqiqnqnqeqrqsq qdqoq qtqhqaqtq.q"

Received on Friday, 24 May 2013 16:44:20 UTC