I managed to do a backface culled solid material, but I need a backface culled mask. I am talking about a mask material that only masks when viewed from one side and is entirely transparent when viewed from the other side.
I am trying to make a dimension changing effect with a growing sphere, that changes the scene inside itself into another one.
Here is what I managed to do with half spheres: http://i.imgur.com/anhP99G.jpg
What I did here was to render winter scene with a sphere shaped mask in the middle, then a spring scene with half globe on the back masking the back wall, and under that one is the winter scene again with negative z-mask half sphere.
But that effect in the screenshot is not enough. You can see mistakes near the edges of the sphere and that only works from one angle and distance. I would need this effect from multiple camera angles.
Best option would be to replace the half spheres with full spheres that only used the back walls for masking.