Intersection contour

[Jerry]

Is it possible to display only the points that two or more 3d objects
have in common? For example, I have a plane intersecting a sphere
and want to show only the circle representing the points that both
have in common.

[farshizzo]

Hi Jerry,

There is no built-in way to do this. This could probably be accomplished through a plugin, but I'm still not exactly sure what you want. Do you have some sample screenshot of the effect you are referring to?

[halley]

I think Jerry is looking for the intersection of two meshes. It's easy for primitives like [ sphere & plane ], but can get pretty tricky when the meshes are more complicated.

Pictured here is [ sphere & cube ] and the contour is already getting to be a strange shape. If either mesh is not manifold (would leak water), then the intersection space is no longer manifold either.

http://halley.cc/blender/intersection.sphere.and.cube.jpg

Except in the most trivial cases, it's not something you can/should try to do in real time with moving objects.

However, there are sometimes some interesting z-buffer tricks which can emulate this kind of work in limited scenarios.