Re: [3d-transforms] Behavior of intersecting layers with transform-style: preserve-3d is undefined and inconsistent across implementations

On Sat, Oct 8, 2011 at 5:23 AM, Chris Marrin <cmarrin@apple.com> wrote:

>
> 2. Whether 3d-transformed elements intersect with other elements (including
> each other and their parent element) in the absence of transform-style:
> preserve-3d. Current Safari behavior is that they do, but an alternative
> proposal would be that they do not, and that 3D transforms are simply a
> painting effect (in other words they'd behave just like 2D transforms).
> However, we'd have to decide whether 3D-transformed elements continue to
> paint in document order, or whether front-to-back order is affected by
> position on the z-axis. If the latter, then you either have to depth-sort by
> some arbitrary point (like the element center point), or you have to buy
> into allowing intersection.
>
>
> Seems reasonable to let flattened layer behave like 2D, and leave the
> preservation of 3D rendering and picking order to the preserves-3d case.
>

This is what Gecko does.

I agree that the rendering of intersecting elements should be normatively
defined. Rather than specify Newell's algorithm I think we can just specify
that for each point in the viewport, the elements are rendered ordered by
the z-position of each  element at that point, using the DOM order to break
ties. Various algorithms can be used to approximate that.

Maybe we should have a note in the spec pointing out that implementation
difficulties mean that in practice, browsers will not be able to produce the
ideal rendering in all cases.

Rob
-- 
"If we claim to be without sin, we deceive ourselves and the truth is not in
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we make him out to be a liar and his word is not in us." [1 John 1:8-10]