Transparent Shader that blocks light as an opaque shader would

In Unity 4 I applied the following shader (originally from Answers, slightly modified) to objects that came between the player character and the main camera in order to make said object transparent - without affecting the lighting/shadows on either side of the object.

Code (CSharp):

1. Shader "Transparent/DiffuseWithShadow" {
2.     Properties {
3.         _Color ("Main Color", Color) = (1,1,1,1)
4.         _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
5.     }
6.     SubShader {
7.         Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent" }
8.         UsePass "VertexLit/SHADOWCOLLECTOR"  
9.         UsePass "VertexLit/SHADOWCASTER"  
10.         LOD 200
11.         Blend SrcAlpha OneMinusSrcAlpha
12.  
13.         CGPROGRAM
14.         #pragma surface surf Lambert addshadow
15.  
16.         sampler2D _MainTex;
17.         fixed4 _Color;
18.    
19.         struct Input {
20.             float2 uv_MainTex;
21.         };
22.    
23.         void surf (Input IN, inout SurfaceOutput o) {
24.             fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
25.             o.Albedo = c.rgb;
26.             o.Alpha = c.a;
27.         }
28.         ENDCG
29.     }
30.    
31.     Fallback "Transparent/VertexLit"
32. }

However in Unity 5 the shader doesn't work the same way. Objects still go transparent, but they also allow light (and shadows) to pass through, which is not ideal. Is there any way I could get the shader working the same way in Unity 5?

From what I've picked up from other threads in this subforum, I'm assuming the "Blend" line is really supposed to go into a Pass block, but I'm not sure how to modify this shader to achieve that, as I'm not well versed in shader programming. If anyone could give me a helping hand with this it would be appreciated.

I've attached two screenshots showing the difference in how the shader works in Unity 4 and Unity 5.

 

Can upload a sample scene using just cubes to show the effect working in 4, I can't quite get a repro working with just what's posted above, I think it's probably something simple by the looks of things.

 

Actually, can you try changing this:

#pragma surface surf Lambert addshadow

ToL

#pragma surface surf Lambert alpha:blend addshadow

It might be the fix, but just a guess.

 

I've attached a sample scene to this post.

In Unity 4, the cube and the area in between the two walls in the scene will only be affected by the point light in between the walls, even if the wall closest to the camera is set to use the custom "DiffuseWithShadow" shader.

In Unity 5, the cube and area in between the walls is affected by both lights.

The difference between how it works and how it should ideally work in Unity 5 can be seen by switching the shader on the wall closest to the camera between the standard shader and the included custom shader. Ideally, the custom shader should affect light and shadow in the same way as the standard shader does.

 

Cool, I won't get a chance to look tonight I don't think but I'll get back to you in the morning.

 

I tried #pragma surface surf Lambert alpha:blend addshadow, though by itself not much changed. However when I tried this and commented out the UsePass "VertexLit/SHADOWCOLLECTOR" line at the same time, I almost got what I wanted, with the exception of the transparent wall now being too much affected by lightsources. The brighter the light shining on it, the harder it is to see through it (because it reflects the light?). Hm.

 

I think it should be easy enough to fix, but I've not got Unity 4 on this machine, leave it with me and I'll let you know by tomorrow.

 

Here you go, on mine it doesn't update the shadows instantly, switching emulation to Shader Model 3.0 and back gets it to re-do the shadows and you should see it working then:

Code (CSharp):

1. Shader "Transparent/DiffuseWithShadow"
2. {
3. Properties {
4.     _Color ("Main Color", Color) = (1,1,1,1)
5.     _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
6. }
7.  
8. SubShader {
9.     Tags {"Queue"="Transparent-1" "IgnoreProjector"="True" "RenderType"="Transparent"}
10.     LOD 200
11.    
12. CGPROGRAM
13. #pragma surface surf Lambert alpha:blend addshadow
14.  
15. sampler2D _MainTex;
16. fixed4 _Color;
17.  
18. struct Input {
19.     float2 uv_MainTex;
20. };
21.  
22. void surf (Input IN, inout SurfaceOutput o) {
23.     fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
24.     o.Albedo = c.rgb;
25.     o.Alpha = c.a;
26. }
27. ENDCG
28.  
29.  
30.  
31.     // Pass to render object as a shadow caster
32.     Pass {
33.         Name "ShadowCaster"
34.         Tags { "LightMode" = "ShadowCaster" }
35.        
36. CGPROGRAM
37. #pragma vertex vert
38. #pragma fragment frag
39. #pragma multi_compile_shadowcaster
40. #include "UnityCG.cginc"
41.  
42. struct v2f {
43.     V2F_SHADOW_CASTER;
44. };
45.  
46. v2f vert( appdata_base v )
47. {
48.     v2f o;
49.     TRANSFER_SHADOW_CASTER_NORMALOFFSET(o)
50.     return o;
51. }
52.  
53. float4 frag( v2f i ) : SV_Target
54. {
55.     SHADOW_CASTER_FRAGMENT(i)
56. }
57. ENDCG
58.  
59.     }
60.  
61.  
62. }
63.  
64. }
65.  

 

Thank you, that seems to be a step (or leap) in the right direction I seem to be having some issues with it, though.

• Whenever I apply the transparent shader to a wall to make it transparent, it appears to be random whether objects behind the the wall are affected by lights from the other side of that wall. Sometimes they are, sometimes they're not. Shadows from shadowcasting objects also pass through the walls in those cases.
• Directional lights and spot lights always seem to affect objects behind transparent walls, no matter what?

Including two screenshots. First seems to work as intended, second does not. Taken in same play session, just by moving camera to re-apply the transparent shader to the wall when they obscure the player:
:

 

Hmmm, this might be a bug. Let me have a bit more of a look, it's either because we need to write to the depth buffer and maybe change the queue, or it is just a bug. I'll come back to you soon.

 

I found a solution that worked for me. It's very simple.

1. Duplicate your transparent wall (you can make it child of your original wall).
2. Remove the new wall's collider because you just want the mesh.
3. Now in the mesh renderer turn cast shadows to "shadows only", it will make the new wall invisible but it will block the light and shadows.

The original wall will keep transparent and will work as before.

I know it's 2021 but I had this problem today and I spent like 1-2 hours finding a solution. I hope it works for you.

 

Thanks! This helped me out. For others who arrive here, bullet point #3 is referring to the original MeshRenderer, not the duplicated one from bullet point #1.