Camera render order desync for depth cubemaps

[Vladimir Sabantsev]

I suspect that there is an issue with cameras render order when using cubemap as a depth attachment.
The output from my demo project may vary depending on how lucky am I while executing it.

Normal (but one with a sharp eye may notice a frame with the floor and ceiling being lit wile the walls have already disappeared):

Unlucky (highly visible issues on the wall):

I can send out the project for debugging on request, but currently my theory is the following:

[Vladimir Sabantsev]

While revisiting this issue in my head today, I have learned after a small research that a geometry shader allows to render into different texture layers with different projection matrices using gl_Layer.

May it actually worth putting additional overhead of geometry shader invocation in order to fit cubemap (or cubemap array) rendering into one pass? 

[Josh]

There is a special extension that does this. Geometry shaders are usually very bad for performance.