Keeping layer constant during animation.

Hi all!

I am trying to animate an ocean around a quite complicated island. The island sits on a separate render layer from the ocean and basically the island will not change during the animation.

Is there a way to prerender the island once, and then combine it with the animated water when I do the final rendering?

I’ve tried the following using only two simple objects: A cube and and a moving sphere.

  1. I first render the (static) cube and save it as an exr-fil.
  2. Then I add this file with an image node and combine this with the render of the sphere using a “greater than” node where I compare the z-value of the render output (containing the sphere) and the “depth”-value of the exr-image node to determine which objects should be in the front in the final composite.

This actually works if the sphere is passing behind or infront of the the cube. However, if the sphere actually goes through the cube it does not work (I only get a pink screen output).

So basically what my question is:
Is it possible to save a render layer and then import it via a node and combine it with another render layer from a completely separate rendering?

I hope I made sense above, but I am very happy to clarify if someone wants to help.

You would bring it in with an image node, but only in BI at this time as Cycles does not support frame update for movies.
You could always composite one scene rendered out over the other in the sequencer or other movie editor. I think that answers part of your question.

Thanks for the reply, but I am not sure that works. Images do not in general contain depth information and it so it is impossible to determine which parts goes behind what.

I did however manage to solve this by moving the static object to an entirely different scene where I render it. Then I load the render layer from that scene into the scene I want to animate and compose them there.

There is “Z Combine” node. This should work better then “greater than” trick. If you pre-render, always use multilayer exr, not the standard one.