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I guess this is more of a general 3D question than specifically of Blender.

How can I separate my scene in layers to render my animation faster on Cycles? Meaning, is there any rule what should be on what layer and how should it be composited? I don't want to spend a huge amount of time rendering the whole set for each frame when I can just render the animation and composite it over the BG.

There's a lot of tutorials on how to do it with stills, but I haven't been able to find anything regarding animation.

Thanks a lot!

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  • $\begingroup$ The methods for stills are done in the compositor, which renders for each frame. Those methods should work. Note that it will be very slow :P $\endgroup$
    – VRM
    Oct 9 '15 at 16:47
  • $\begingroup$ I managed to do a kind of a setup that renders the character animation and it's shadow on the ground and then combines it with a pre-rendered BG and FG. It speed up the render considerably, of course, but I don't know if there's some kind of mainstream process for this. This process only allows still shots, of course, otherwise you'd have to render the BG and FG for every frame $\endgroup$
    – Francisco Mariz Rodrigues
    Oct 9 '15 at 16:58
  • $\begingroup$ You can render them out as animations, you can use video sequences in the compositor $\endgroup$
    – VRM
    Oct 9 '15 at 17:02
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    $\begingroup$ Blender guru has an article that might interest you blenderguru.com/articles/… $\endgroup$
    – user1853
    Oct 10 '15 at 15:05
  • $\begingroup$ thanks @cegaton ! I had seen this before. And a bunch of others that explain the process I'm trying to achieve but simply don't work for some reason or other. $\endgroup$
    – Francisco Mariz Rodrigues
    Oct 13 '15 at 9:04
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So here's what I came up with:

Node Setup

Basically, if the shot's fixed, and the camera doesn't move I pre-render the BG and the FG (The first 2 image inputs). Then, with render layers:

Animation Render Layer: I put everything that has to be animated or interacts with the animation on visible layers and the rest just influencing those objects, but NOT VISIBLE.

Shadows Render Layer: Has a basic ground plane to receive the shadows with Shadows and AO render passes enabled. Here, I EXCLUDE the BG and FG. enter image description here

Then, the Shadows Layer needs a Dilute/Erode node

And voilá! From about 1-2 hours of render time to 5 minutes per frame. Again, this requires fixed shots.

Still...I'm no compositor wiz and this surely needs improving! For example, the Shadow Pass simply doesn't work...why is it there in the first place. Only the AO works. But it would make sense that the Shadows pass is what enables the shadow only calculation in the first place.

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  • $\begingroup$ Apparently, the Shadow pass only works with Lamps and not with emission planes? $\endgroup$
    – Francisco Mariz Rodrigues
    Oct 13 '15 at 14:24
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    $\begingroup$ To ask a new question please make a new post. $\endgroup$
    – user1853
    Dec 12 '15 at 17:16

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