Visibility/occlusion by object

[tricky]

I have a small sphere within a larger box.
How do I achieve a single-pass render whereby the small sphere is ALWAYS visible, i.e. the box is 'matted' out by the sphere irrespective of the view it is seen from?

[vlado]

You can invert the normals of the box and use the "Force back-face culling" from the global switches rollout to remove the back-side faces of the box.

Best regards,
Vlado

[tricky]

Mmm. Interesting theory. However, now my box renders quite dark, and the sphere inside is also dark...I still need the box to render absolutly normally with just a 'hole' cut out for the sphere to show through.

[vlado]

Ah, I see. Not sure how you can do that without rendering in separate passes though.

Best regards,
Vlado

[tricky]

Anyone got any suggestions - I'm sure you should be able to do this. Something to do with grabbing the matte of a particular object at render time and applying it to the opacity/visibility of another specific object.