I'm new to Motion (5) but have watched many tutorials and have successfully created a handful of very simple 2D projects. What I am trying to do now is to create a 3D wall (with z-space thickness) which has a window which I can dolly the camera through as if the viewer is walking toward it. I have this working using a Color Solid as the wall with a mask shape added to lay out the window. I can "see" through the window what is on the other side (a video layer set back in z-space from the wall) however there are no "inner edges" to the window, it's just a flat plane.
I created a replicator on the wall, set it to replicate in a line and increased the number of points. When I orbit the camera around I can see the wall has thickness and appears solid, but dollying the camera through the window still doesn't show the inner edges (the z-space edges) of the window.
Thank you Mark, I will try that. My window was non-rectangular (rounded top) which is why I used an image mask to cut it out of the wall. I'll need work out how to build a curve with depth for that top edge, or else try not to be so fancy on my first try. :-)