standard metallic shader map

hi all!
I need to do somethings on a custom shader: I created a standard shader and looks like this:

Code (CSharp):

1. Shader "gRally/grsCarTemporary2"
2. {
3.     Properties {
4.         _Color ("Color", Color) = (1,1,1,1)
5.         _MainTex ("Albedo (RGB)", 2D) = "white" {}
6.         _Glossiness ("Smoothness", Range(0,1)) = 0.5
7.         _Metallic ("Metallic", Range(0,1)) = 0.0
8.     }
9.     SubShader {
10.         Tags { "RenderType"="Opaque" }
11.         LOD 200
12.        
13.         CGPROGRAM
14.         // Physically based Standard lighting model, and enable shadows on all light types
15.         #pragma surface surf Standard fullforwardshadows
16.  
17.         // Use shader model 3.0 target, to get nicer looking lighting
18.         #pragma target 3.0
19.  
20.         sampler2D _MainTex;
21.         struct Input {
22.             float2 uv_MainTex;
23.         };
24.  
25.         half _Glossiness;
26.         half _Metallic;
27.         fixed4 _Color;
28.  
29.         // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
30.         // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
31.         // #pragma instancing_options assumeuniformscaling
32.         UNITY_INSTANCING_CBUFFER_START(Props)
33.             // put more per-instance properties here
34.         UNITY_INSTANCING_CBUFFER_END
35.  
36.         void surf (Input IN, inout SurfaceOutputStandard o) {
37.             // Albedo comes from a texture tinted by color
38.             fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
39.             o.Albedo = c.rgb;
40.             // Metallic and smoothness come from slider variables
41.             o.Metallic = _Metallic;
42.             o.Smoothness = _Glossiness;
43.             o.Alpha = c.a;
44.         }
45.         ENDCG
46.     }
47.     FallBack "Diffuse"
48. }
49.  

now I need to add a separate texture that contains the metallic map... is not a problem, but how can I pass to the standard pipeline to get the metallic not by _Metallic slider but by the alpha channel of the metallic texture?

thanks in advance

 

The "real" Standard shader stores the metallic value in the red channel of the Metallic texture, and the smoothness in the alpha, btw. There's no reason you have to stick to that convention for Surface shaders though, if storing the metallic in the alpha is what you want to do.

However the answer to your question is "the same way you would in any other shader". Not helpful, I know, but if that's the question you're asking then you probably need to start reading up on shaders.
http://www.alanzucconi.com/2015/06/10/a-gentle-introduction-to-shaders-in-unity3d/

 

thank again @bgolus
I've solved, using this code:

Code (CSharp):

1. // spec
2. fixed4 cSpec = tex2D(_MetallicGlossMap, IN.uv_MainTex);
3. o.Metallic = cSpec.rgb;
4. o.Smoothness = _Glossiness * cSpec.a;

my error was that I think that I was able to use the code inside the standard shader just adding some defines like

Code (CSharp):

1. #pragma shader_feature _METALLICGLOSSMAP

but no, I needed to write the code..

thanks