Transparent shaders > rendertexture with alpha

Hi experts!

I would like to compose a scene with several planes, having a PNG texture with transparency (not just cutout, true alpha).

This scene has a camera rendering to a Rendertexture containing alpha.

In another scene, I would like to be able to put a plane with that rendertexture, in front other planes (eventually also containing alpha, etcetera). This should render to a rendertexture with correct alpha again.

Graphical explanation:





What shaders would I need to be able to do this? My current transparent shader doesn't work with every setting I tried on the camera for clearing the background.

My shader:

Code (JavaScript):

1. Shader "Mode/Alpha with Mask" {
2.     Properties {
3.       _MainTex ("Texture", 2D) = "white" {}
4.       _BumpMap ("Texture", 2D) = "white" {}
5.       _Color ("Main Color", Color) = (1.0, 1.0, 1.0, 1.0)
6.       _AddColor ("Add Color", Color) = (0.0, 0.0, 0.0, 1.0)
7.       _Mode("Mode", float) = 0.0
8.     }
9.     SubShader {
10.       Tags { "RenderType" = "transparent" "Queue"="transparent"}
11.       ZWrite Off
12.       //Lighting Off
13.       CGPROGRAM
14.       #pragma target 3.0
15.       #pragma surface surf Unlit noambient alpha
16.       struct Input {
17.         float2 uv_MainTex;
18.         float2 uv_BumpMap;
19.         fixed4 _Color;
20.         fixed4 _AddColor;
21.         float _Mode;
22.       };
23.       sampler2D _MainTex;
24.       sampler2D _BumpMap;
25.       fixed4 _Color;
26.       fixed4 _AddColor;
27.       float _Mode;
28.         inline half4 LightingUnlit (SurfaceOutput s, half3 lightDir, half atten) {
29.             float4 c;
30.             c.rgb = s.Albedo;
31.             c.a = s.Alpha;
32.             return c;
33.         }
34.  
35.         inline half4 LightingUnlit_PrePass (SurfaceOutput s, half4 light) {
36.             float4 c;
37.             c.rgb = s.Albedo;
38.             c.a = s.Alpha;
39.             return c;
40.         }
41.      
42.      void surf (Input IN, inout SurfaceOutput o) {
43.           fixed4 tex = tex2D (_MainTex, IN.uv_MainTex);
44.           float4 c = tex2D(_BumpMap, IN.uv_BumpMap);
45.         float3 output = tex.rgb * _Color.rgb;
46.         float grey = (c.r + c.g + c.b) / 3.0;
47.         float alpha = tex.a * _Color.a * grey * c.a;
48.         o.Alpha = alpha;
49.         o.Emission = output.rgb + _AddColor.rgb;
50.       }
51.      
52.      
53.       ENDCG
54.     }
55.     Fallback "Unlit/Texture"
56.   }

 

Not entirely sure since I don't have much experience with surf shaders(they end up as vert/frag anyway) but I don't see you indicating Blend mode.

 

Thanks for your reply, I'll dive into the world of 'blend modes' to see if that's something I've missed!