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[css3-3d-transforms] preverve-3d and 'Z position' clarifications

From: Sylvain Galineau <sylvaing@microsoft.com>
Date: Wed, 8 Sep 2010 22:57:39 +0000
To: "www-style@w3.org list" <www-style@w3.org>
Message-ID: <045A765940533D4CA4933A4A7E32597E27CACE33@TK5EX14MBXC120.redmond.corp.microsoft.com>
I am trying to understand preserve-3d's semantics and learning 3D in general at the same time so
forgive any na´ve questions.

In the current WD, much of preserve-3d and the relationship of the Z axis with the CSS stacking
context model seems to be defined in the non-normative introduction [1]. In particular:

# The position on the Z axis of a transformed element does not affect the order within a stacking 
# context. With elements at the same z-index, objects are drawn in order of increasing z position.

..is not something that belongs to a non-normative section. 

I assume the Z position of non-transformed elements is implied to be 0 but I couldn't find any
explicit mention of that.

It is, however, not explicitly defined how the Z position of an element is calculated. Is it the
Z coordinate of the element's top-left ?
Now, if we preserve the drawing order then will an element with a lower z-index and a higher Z
position find itself covered by a higher z-index element with a lower Z position ? An element
with a lower z-index could also intersect one with a higher z-index, right ?

[1] http://dev.w3.org/csswg/css3-3d-transforms/#introduction
Received on Wednesday, 8 September 2010 22:58:20 UTC

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