layers and zindex in Safari

[David Hyatt]

This is how WinIE behaves with negative z-index, and this was the 
source of bugs on several sites.  (I'll try to hunt up the sites for 
reference)

Also, the CSS2.1 spec is going to clarify the behavior of negative 
z-index, and the behavior of painting the background at -infinity 
(behind the negative z-index children) is going to be the correct 
behavior.

Here is the current text from the next iteration of the 
not-yet-published CSS2.1 draft.

"Each stacking context consists of the following stacking levels (from 
back to front):
	 1.  	the background and borders of the element forming the stacking 
context.
	 2.  	the stacking contexts of descendants with negative stack levels.
	 3.  	a stacking level containing in-flow non-inline-level descendants.
	 4.  	a stacking level for floats and their contents.
	 5.  	a stacking level for in-flow inline-level descendants.
	 6.  	a stacking level for positioned descendants with 'z-index: 
auto', and any descendant stacking contexts with 'z-index: 0'.
	 7.  	the stacking contexts of descendants with positive stack levels."

Basically this gives you total control, since you can establish a 
stacking context yourself (by specifying an integer z-index), thus 
ensuring negative z-index children paint above your background, or you 
can specify a z-index of auto in which case the negative z-index 
children will be sorted in your parent's stacking context and will 
paint behind your background.

dave

On Friday, August 29, 2003, at 3:29 AM, Lars Knoll wrote:

> Hi,
>
> I found the following comment in safaris render_layer code:
>
>     // Find out if we have any elements with negative z-indices in this
> stacking context.
>     // If so, then we need to split our layer in two (a background 
> layer and a
> foreground
>     // layer).  We then put the background layer before the negative 
> z-index
> objects, and
>     // leave the foreground layer in the position previously occupied 
> by the
> unsplit original.
>
> The code which does this doesn't seem to make sense to me. Negative and
> positive z-indices seem to be treated differently concerning the 
> painting of
> backgrounds even though the CSS specs treats them equally (the way you
> currently trat positive z-indices).
>
> Could you tell me the reason why you treat these differently?
>
> Thanks,
> Lars
>
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