Shader request: invisible, but occluding and receives shadows?

Hi all, I have a need for a shader to be used in augmented reality applications that occludes what's behind, is transparent (so that the video feed "behind" the scene shows through), BUT can receive real-time shadows to be drawn overtop of the video feed. Is this kind of thing possible in Unity? Or am I going to be stuck with using blob-shadows for these things?

 

I'm still looking for a shader like this. Anyone have any ideas?

 

So, you will render the geometry and the video will be the background?

If so, take a look at this quick shader, which is veeeery limited (it won't look too nice with other than a plane as the occluding object, one directional light pointing almost directly to the plane, and also the shadows will be completely black). Depending on what you exactly need it may or may not work for you, or may be an starting point to do something better. Basically, it's a surface shader with a white color, and a blending operation which draws the minimum color between the object and the background (which most of the time will be the background):

Code (CSharp):

1. Shader "Custom/Occluder"
2. {
3.     SubShader
4.     {
5.         Tags
6.         {
7.             "Queue" = "Background+1"
8.         }
9.  
10.  
11.         BlendOp Min
12.         Blend One One
13.    
14.  
15.     CGPROGRAM
16.         #pragma surface surf Lambert
17.    
18.    
19.         struct Input
20.         {
21.             float Nothing;
22.         };
23.    
24.    
25.         void surf(Input IN, inout SurfaceOutput o)
26.         {
27.             o.Albedo = half4(1, 1, 1, 1);
28.         }
29.     ENDCG
30.     }
31.  
32.  
33.     Fallback "VertexLit"
34. }

 

Thanks, that is pretty much what I was looking for! There were some side effects, but they are ones that in hindsight I should have seen coming... I may be able to compensate for them using layer masks.

 

Would there be any harm in doing:

o.Albedo=half4(65520, 65520, 65520, 65520);

instead, so that it was sure to work with HDR as well?

 

I tried it, but it made all the shadows stop working. I don't anticipate it really needing to work with HDR anyhow, TBH.