Invisible Shadow-only Shader

Hi!

I am trying to build a shader that will only cast a shadow but not render the object itself. There are various attempts in Unity Answers, the forums and various spots on the web, but nobody actually seems to have achieved this effect.

The closest I got so far is this:

Code (CSharp):

1. Shader "Custom/Shadow Only" {
2.   SubShader {
3.  
4.     Pass {
5.       Tags { "LightMode" = "ShadowCaster" }
6.  
7.       CGPROGRAM
8.  
9.       #pragma vertex vert
10.       #pragma fragment frag
11.  
12.       float4 vert(float4 v:POSITION) : SV_POSITION {
13.         return mul (UNITY_MATRIX_MVP, v);
14.         //return float4(0.0,0.0,0.0,1.0);
15.       }
16.  
17.       fixed4 frag() : COLOR {
18.         //discard;
19.         return fixed4(0.0,0.0,0.0,1.0);
20.       }
21.  
22.       ENDCG
23.     }
24.  
25.   }
26. }

As you will notice, it obscures the shadow of any object behind it and itself.
For some reason, there's also a strange moiré pattern on some of its faces:

 

It's work properly only with deferred rendering, at least in U5b. As far i remember in 4.6 it's work fine.

Code (csharp):

1.  
2. Shader "Custom/ShadowOnly"
3. {
4.     Properties {
5.         _MainTex ("Base (RGB)", 2D) = "white" {}
6.     }
7.     SubShader
8.     {
9.         Pass {
10.         Name "ShadowCaster"
11.         Tags { "LightMode" = "ShadowCaster" }
12.      
13.         Fog {Mode Off}
14.         ZWrite On ZTest LEqual Cull Off
15.         Offset 1, 1
16.  
17.         CGPROGRAM
18.         #pragma vertex vert
19.         #pragma fragment frag
20.         #pragma multi_compile_shadowcaster
21.         #include "UnityCG.cginc"
22.  
23.         struct v2f {
24.             V2F_SHADOW_CASTER;
25.         };
26.  
27.         v2f vert( appdata_base v )
28.         {
29.             v2f o;
30.             TRANSFER_SHADOW_CASTER(o)
31.             return o;
32.         }
33.  
34.         float4 frag( v2f i ) : SV_Target
35.         {
36.             SHADOW_CASTER_FRAGMENT(i)
37.         }
38.         ENDCG
39.  
40.         }
41.     }
42. }
43.  
44.  

add
Well is some with what inside answers link.

 

Thank you.

In deferred mode, my attempt seems to work, too. I'll go with mine for now but keep this bookmarked in case I run into trouble. If anyone has a suggestion for a method that works in both forward and deferred rendering, I'm still interested

 

mouurusai's solution appears to work just fine for me in forward rendering mode too.

 

Flailer, what version of Unity3D you are use?

 

Tested it on the free version.

 

Version number
It's doesn't work in 5.0.0b14

 

4.5.4f1 lol they have changed the way shadows work under the hood in unity 5.0 though, Ill have a play with this at work when we try the beta of 5.0 in a week or so

 

Not sure where I found it but just disable receive shadows on the object and try this:

Code (CSharp):

1. Shader "Transparent/InvisibleShadowCaster"
2. {
3.      Subshader
4.      {
5.          UsePass "VertexLit/SHADOWCOLLECTOR"  
6.          UsePass "VertexLit/SHADOWCASTER"
7.      }
8.      Fallback off
9. }