Depth sorting not working in mono mode

[jcarpenter]

In mono mode the occlusion of elements is defined by element ordering and/or css z-index. The transform values do not seem to have any effect.

This effects both Firefox Nightly June 30 CSS VR build and latest Chrome.

Test case: http://mozvr.github.io/cssvr-experiments/20150802-04/index.html

The same scene viewed in VR mode renders correctly.

Mono mode:

VR mode:

[jcarpenter]

We've seen this issue before in Firefox. Compare the following CodePen between FF and Chrome: http://codepen.io/suez/pen/GJKRPN

[dmarcos]

This looks the same bug as https://bugzilla.mozilla.org/show_bug.cgi?id=1175311

It is still present in the 2015-06-30 build.

On mono mode we're setting the projection matrix of the parent element instead of relying on the css perspective attribute. This is why the bug doesn't manifest on stereo. In the bug above, @kearwood suggested to use a w preserving projection matrix. I'm not sure what that exactly means. I asked him for clarification on bugzilla.