css z-index lost after webkit transform translate3d

Question

I have two absolutely positioned div elements that overlap. Both have set z-index values via css. I use the translate3d webkit transform to animate these elements off the screen, and then back onto the screen. After the transform, the elements no longer respect their set z-index values.

Can anyone explain what happens to the z-index / stack-order of the div elements once I do a webkit transform on them? And explain what I can do to keep the stack-order of the div elements?

Here is some more information on how I am doing the transform.

Before the transform, each element gets these two webkit transition values set via css (I am using jQuery to do the .css() function calls:

element.css({ '-webkit-transition-duration': duration + 's' });
element.css({ '-webkit-transition-property': '-webkit-transform' });

The element is then animated using the translate3d -webkit-transform:

element.css({ '-webkit-transform': 'translate3d(' + hwDelta + 'px, 0, -1px)' });

Btw, I have tried setting the 3rd parameter of translate3d to several different values to try to replicate the stack-order in the 3d space, but to no luck.

Also, iPhone/iPad and Android browsers are my target browser that this code needs to run on. Both support webkit transitions.

Answer 1

This might be related to: https://bugs.webkit.org/show_bug.cgi?id=61824

Basically when you apply a 3D transform on the z-axis, the z-index can't be accounted for anymore (you're now in a 3 dimensional rendering plane, use different z-values). If you want to switch back to 2D rendering for child elements, use transform-style: flat;.