Re: [css-compositing] test suite for grouping

On Apr 18, 2013, at 8:00 AM, Rik Cabanier <cabanier@gmail.com> wrote:

> 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.


I agree with Robert that we should not lock in grouping behavior when we don't have to.

Is the problem here that it's the grouping of elements which do _not_ have the blending properties applied to them that's the issue? Maybe you'll have to add a property for things that need to behave predictably when something on top of them is blended.

Simon