css z-index lost after webkit transform translate3

问题:

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.

回答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;.

回答2:

This is most definitely related to the bug noted by samy-delux. This should only affect any elements which are positioned as absolute or relative. In order to remedy the issue, you can apply the following css statement to every element which is positioned this way and is causing issues:

-webkit-transform: translate3d(0,0,0);

This will apply the transform to the element without actually doing a transformation, but affecting its render order so it is above the element causing the issue.

回答3:

Bit Late to this but try putting on the elements that have lost their Z-index placing the following, I had an issue when doing some parallax stuff recently and this helped massively.

transform-style: preserve-3d;

This saves putting

transform: translate3d(0,0,0);

On other elements which puts more strain on the GPU

回答4:

Waiting to see the example

Have you tried to do a transform scale(1)? I remember to had a similar problem, and I had to re-arrange the html order of elements, and utilise a transform that I didn\'t need it just because the z-index of the use of transform changed.

If I am not in error, every time that you use a transform, it become the highest z-index available, and it is ordered by the nearest element of html is to the start of the tag. So from up to below.

I hope that this help

回答5:

z-index will work against 3d transformed divs if you style the stackable element with -webkit-transform: translateZ(0px);

Snippet on codepen -> http://codepen.io/mrmoje/pen/yLIul

In the example, the buttons stack up and stack down raise and lower the footer\'s z-index (+/-1) against the rotated element (an img in this case).

回答6:

I haven\'t been able to reproduce the problem you describe here. Regardless of what I do, the z-index value is retained throughout all transforms. I\'m testing using Chromium (Google Chrome).

The third argument of the translate3d function manipulates the z-axis of the element. The concept is similar to, but not exactly the same as, the z-index... Elements with a lower z-axis are under elements with a higher value.

I know you tried values of the third argument to match your intended z-index, but the problem is that the z-axis doesn\'t seem to change during CSS3 animation. In the following example, the hovered element should be on top, but #element_a stays on top.

If I add a z-index to both the regular selector and the :hover selector, it seems to work and allow the hovered element to be top-most.

Although it\'s not exactly what you were looking for, this behavior provides a solution. You just need to use translate3d and z-index to set the order for the initial rendering.

<style>
    div {
        width: 300px;
        height: 150px;
        background-color: white;
        border: 5px outset gray;
        float: left;
        margin: 20px;
        -webkit-transition: 2s;
    }

    #element_a {
        -webkit-transform: translate3d(0, 0, 50px);
    }
    #element_b {
        -webkit-transform: translate3d(0, 0, 100px);
    }

    #element_a:hover {
        -webkit-transform: translate3d(100px, 0, 60px);
    }

    #element_b:hover {
        -webkit-transform: translate3d(-100px, 0, -60px);
    }
</style>
<body>
    <div id=\"element_a\">
        <img src=\"http://www.google.com/intl/en_com/images/srpr/logo3w.png\">
    </div>
    <div id=\"element_b\">
        <img src=\"http://www.google.com/intl/en_com/images/srpr/logo3w.png\">
    </div>
</body>

回答7:

Another way around this is that you can create a parent element and apply all other transitions related to it:

# Apply transitions to a parent div
<div>
  # This image z-index -1 
  <img src=\"foo\"/>

  # This image z-index -3
  <img src=\"bar\"/>

  #This image z-index -2
  <img src=\"gg\"/>
</div>

JsFiddle