Re: [css3-transforms] 3D transform updates

On Tue, Oct 28, 2014 at 12:27 PM, Simon Fraser <smfr@me.com> wrote:

> On Oct 27, 2014, at 3:36 PM, Robert O'Callahan <robert@ocallahan.org>
> wrote:
>
> > Thanks for doing this! The spec is much improved.
> >
> > Putting all non-3D content of a 3D rendering context at the very bottom
> of z-order seems simpler and more robust than putting it at z=0 as the spec
> currently says. Authors can usually opt into the z=0 effect by wrapping
> content in a trivial 3D transform.
>
> Agreed, and this would address issue 3. It’s just unfortunate that it
> doesn’t match the behavior of z-index: -1, but I’m willing to live with
> that. We also need to consider how 3D transformed elements interact with
> 2D-transformed elements (which might have 3D-transformed descendants); in
> WebKit at least, a 2D-transforemd element with a 3D-transformed descendant
> gets popped into a texture, so would start interleaving.
>

Isn't that simple to fix by forcing that 2D-transformed element to flatten,
and then giving its layer a z coordinate that forces it to the back of the
depth buffer?

> There is one case where they can't: as written, a preserve-3d child of
> the root element can be partially behind and partially in front of a
> 'position:fixed' element. Is that something we want to support --- or
> something we explicitly *don't* want to support?
>
> You mean a 3D-transformed child of the root can intersect a
> position:fixed? I don’t see an issue with that offhand, but we should make
> sure that it’s possible to get the position:fixed to always be over
> everything else and not get intersected, with the right flattening.
>

If we adopt my proposed change, then a 3D-transformed child of the root
can't intersect a position:fixed. So whether we want to support that or not
is an important question.

Rob
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