CSS Filters break 3D transforms

Question

I was experimenting with CSS transforms when I found that filters flatten the transforms, just like transform-style: flat.

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Answer 1

As per W3C Transforms Spec:

The following CSS property values require the user agent to create a flattened representation of the descendant elements before they can be applied, and therefore override the behavior of transform-style: preserve-3d:

overflow: any value other than visible.

filter: any value other than none.

clip: any value other than auto.

clip-path: any value other than none.

isolation: used value of isolate.

mask-image: any value other than none.

mask-box-image-source: any value other than none.

mix-blend-mode: any value other than normal.

The computed value of transform-style is not affected.

This is the reason why the 3D transforms are broken and the layers are flattened when you toggle on the filters. The one workaround that I know for this situation is creating the entire cube using sibling elements and apply the filter on the sibling elements directly instead of applying on the parent.

var toggleFilter = function() {
  var div = document.getElementById("cube")
  if (div.className == "cube") {
    div.className = "cube filter"
  } else {
    div.className = "cube"
  }
}

* {
  transform-style: preserve-3d
}
div.cube {
  position: relative;
  height: 100px;
  width: 100px;
  transform: rotateX(45deg) rotateZ(45deg);
}
div.face0 {
  position: absolute;
  content: '';
  height: 100%;
  width: 100%;
  top: 0px;
  left: 0px;
  background: blue;
  border: solid 2px black;
  box-sizing: border-box;
}
div.face1 {
  content: "";
  height: 100px;
  width: 100px;
  background: green;
  transform: rotateY(90deg) translateZ(50px) translateX(50px);
  border: solid 2px black;
  box-sizing: border-box;
}
div.face2 {
  content: "";
  height: 100px;
  width: 100px;
  background: red;
  transform: rotateY(90deg) rotateX(-90deg) translateZ(-50px) translateX(50px);
  border: solid 2px black;
  box-sizing: border-box;
}
div.perspective {
  perspective: 900px;
  position: absolute;
  margin: 50px;
}
.filter .face0,
.filter .face1,
.filter .face2 {
  filter: opacity(25%);
  -webkit-filter: opacity(25%);
}

<div class="perspective">
  <div id="cube" class="cube">
    <div class="face0"></div>
    <div class="face1"></div>
    <div class="face2"></div>
  </div>
</div>
<button onclick="toggleFilter()">Toggle .Filter</button>