How do I render objects behind other objects? + more questions [SOLVED]

Problem:

I am trying to create an animation with a castle and some water and trees around it.
Unfortunatly, the water with all its reflections and stuff like that, and the trees, takes up render time added to rendering the castle.

Therefore, I’d like to split my render, so that I can render my castle, then rendering the water, then the trees and so on.

Finally, I’d like to composite these many images (png files) together.

However, I know that I will now have to create these png files to have alpha transparency where there is no picture or where another object is masking it out. It is the latter that is troublesome:

How do I mask out objects?

This simple render just about sums it up:


You have the Monkey, a Cube and a Plane casting reflections.

What I want is to

  1. Only render the plane with the reflections of the Cube and Monkey, in one render animation.

  2. Render the Cube, and ONLY the Cube.

  3. And now the troublesome: I want to render only the part of the Monkey that is not covered/masked by the Cube. The remaing part of the image must be alpha/transparent/void.

How do I do this?

Put the objects on separate layers and use Render layers
For the monkey you will need to use a mask layer as well to block out the area behind the cube



See attached blend file

Attachments

Render passes.blend (115 KB)

Thank you so much. Initially I could only get a cube, until I realized I had to select “Monkey” in the list in the rendered image.