Re: [css-compositing] test suite for grouping

On Thu, Apr 18, 2013 at 7:12 AM, Robert O'Callahan <robert@ocallahan.org>wrote:

> On Fri, Apr 19, 2013 at 2:01 AM, Dirk Schulze <dschulze@adobe.com> wrote:
>
>> On Apr 18, 2013, at 6:31 AM, Robert O'Callahan <robert@ocallahan.org>
>> wrote:
>> > Maybe you misunderstood me. I don't want to guarantee that the Gecko
>> test results won't change in the future. We need to be able to change
>> grouping to adjust our optimizations.
>>
>> To make this specification successful, we need to agree on some rules
>> about grouping.
>
>
> Which means that these features may severely constrain browser
> optimizations in the future. And that means we have to consider whether
> it's worth having the features as currently designed.
>

If there is no blending, the browser can do whatever it wants (as it
currently does). Only when there's blending should it do something special.


>
> Maybe we could make progress if we introduced a CSS property that forces
> its element to be a group and stacking context, *and* forces all its
> children to be groups and stacking contexts, and then we say that
> blending/compositing only works on those children, and that only the
> siblings of a blended-composited element can be part of the background that
> we blend/composite into.
>

That seems like it would introduce a lot of overhead. Why not simply list
the cases where we want grouping and implement that.
As some testcases point out, we might even want a group within an element
so solving things with just stacking contexts won't work.