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To make a forest for a project I'm working on I am using simplified cutout trees made from three intersecting tree image planes with transparency. these have the three planes spaced 60 degrees apart sharing a vertical central axis. I'm using Cycles.

The issue is that when rendered, the planes cast shadows on the other planes of the same tree, which pretty much ruins the illusion. The shadows cast on the ground are OK, just not the ones falling on the tree itself cast by other parts of the same tree.

I tried using an emission shader, and get pretty good results but only so long as the tree isn't being shadowed by something else (in that case, they seem to glow like they are radioactive).

Is there a way to configure the material nodes for cycles such that the object doesn't cast shadows on itself, but allows other objects to cast shadows on it, and allows it to cast shadows on other objects? Any other approach to accomplish this than the material configuration?

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    $\begingroup$ Hi. The question is not obvious. I have tried the config you describe and it seems I do not encounter your problem. Can you upload your file (blend-exchange.giantcowfilms.com) or some screen shots ? $\endgroup$
    – lemon
    Commented Aug 24, 2016 at 18:44

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You can avoid casting shadows yet still receive shading by using the Light Path node along with a Transparent shader: Material that casts no shadows

Unfortunately, the only way I can think of to cast shadows on other objects but not from itself is to use render layers and create two passes - one with trees that have a material that casts shadows and layer with threes that cast no shadows, and use an object index mask to merge them.

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  • $\begingroup$ Thank you - that did the trick - two passes utilizing the ID mask. I was halfway there myself when I read your post. I'd like to show you the result but I'm new here and don't know how to upload a screenshot/image. $\endgroup$
    – Chris Woodbury
    Commented Nov 6, 2016 at 18:33
  • $\begingroup$ What if you use a material index in the shader nodes? I am still trying to find out if this is possible with only a node setup. $\endgroup$
    – Coby Randal
    Commented Feb 28, 2019 at 15:12
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Another Very Unsophisticated but simple method that worked for me, after finish your scene:

  1. Duplicate the desired object

  2. go to Object tab > Cycles setting > ray visability, check 'shadow' for one object and uncheck 'camera ray', do the opposite for the other.

3.flat one of the duplications (the 'shadow') to be plane, face the light source.

I did it in order to save render time.

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You might want to switch to using Billboards. You can use a single tree image and arrange for it to face the camera using a Locked Track constraint.

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  • $\begingroup$ Good suggestion. I am planning to create far-field HDRs for my background, and planned to do something like this at that distance. The project is an animation with aerial POV, so maybe will use 3-panel trees mid field to avoid weird turning tree effects. Thanks for the hint on how to do it. $\endgroup$
    – Chris Woodbury
    Commented Nov 4, 2016 at 20:50

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