Help with Shadow(s) in Blender (Cycles)

Question

Hello Blender community,

I ran into a problem.... What I want is to exclude the shadow that is cast by object 1on object 3. But the shadow from object 1 on object 2 must remain. How do I Fix this problem?

Hope someone can help

Answer 1

When the floor plane should receive no shadows at all, you could use this quick fix:

Remove all shaders from your ground material, and plug an RGB node directly into the Surface Pin of the Material Output. This way, only the color of the plane will be displayed, but there will be absolutely no shading (shadows, reflections, etc.) without BSDFs.

If you also want the Sphere to cast a shadow on the ground, things get rather complicated, as Gordon Brinkmann already mentioned.

Answer 2

I think you need to use view layers and the compositor. It's a bit messy but very powerful.

EDIT:

• In the example below I created three collections (RMB -> New over
  Collection in the outliner editor) then moved each object so it was
  in its own collection.
• I then created a new view layer, called ViewLayer_001 (click on the overlapping square logo right at the top of the outliner editor)
• With the original ViewLayer selected, I disabled the collection with the vertical plane casting the shadow. For this view layer there is just the icosphere casting a shadow onto the horizontal plane.
• With ViewLayer_001 selected I set the collection with the horizontal plane to holdout. (It's easier to see what's going on if you select the filter at the top of the outliner and add the holdout column, but you can set these with the RMB menu) This layer then renders the icosphere and vertical plane but the horizontal plane is transparent. (alph = 0)
• I then opened a compositor editor, toggled 'use nodes' at the top, then duplicated the render layers node and changed the duplicate to ViewLayer_001. I then added a color -> alpha over node to composite the two.

You might be able to follow the video for my chapter 13 in get-into-blender.com - the video is rather quick without the book, and doesn't answer your question exactly, but the view layer stuff starts after the first minute or so!

Here's a simple blend file with three objects that does what I think you want.