Shader Alpha Cutout

Unity Engine
1

My app currently uses multiple shaders based on users selection. I wanted to add a feature to each shader that will cutout parts of the object based on an alpha image.

In my shader below, you’ll notice I have a separate pass in the end of the cutout, this is basically adding the image on top of the model over the existing color, I want to have it cutout instead of actually drawing the image over the material. I would even settle with having the reverse effect where the alpha portion would be where it shows the original material.

Shader "Opaque Reflective"
{
    Properties
    {
        _BaseColor("Base Color", Color) = (1.0, 1.0, 1.0, 1.0)
        _DetailColor("Detail Color", Color) = (1.0, 1.0, 1.0, 1.0)
        _DetailMap("Detail Map", 2D) = "white" {}
        _DetailMapDepthBias("Detail Map Depth Bias", Float) = 1.0
        _DiffuseColor("Diffuse Color", Color) = (1.0, 1.0, 1.0, 1.0)
        _DiffuseMap("Diffuse Map", 2D) = "white" {}
        _Cutout("Cutout", 2D) = "" {}
        _NormalMap("Normal Map", 2D) = "bump" {}
        _ReflectionColor("Reflection Color", Color) = (1.0, 1.0, 1.0, 1.0)
        _ReflectionMap("Reflection Map", Cube) = "" {}
        _ReflectionStrength("Reflection Strength", Range(0.0, 1.0)) = 0.5
    }

    SubShader
    {
        Tags
        {
            "Queue" = "Geometry"
            "RenderType" = "Opaque"
        }

        Blend Off
        Cull Back
        ZWrite On

        CGPROGRAM
        #pragma target 3.0
        #pragma surface SurfaceMain Lambert vertex:VertexMain

        float4 _BaseColor;
        float4 _DetailColor;
        sampler2D _DetailMap;
        float _DetailMapDepthBias;
        float4 _DiffuseColor;
        sampler2D _DiffuseMap;
        sampler2D _Cutout;
        sampler2D _NormalMap;
        float4 _ReflectionColor;
        samplerCUBE _ReflectionMap;
        float _ReflectionStrength;

        struct Input
        {
            float depth;
            float2 uv_DetailMap;
            float2 uv_DiffuseMap;
            float2 uv_NormalMap;
            float3 worldRefl;
            INTERNAL_DATA
        };

        void SurfaceMain(Input input, inout SurfaceOutput output)
        {
            output.Normal = UnpackNormal(tex2D(_NormalMap, input.uv_NormalMap));

            float3 reflectionColor = texCUBE(_ReflectionMap, WorldReflectionVector(input, output.Normal)).rgb * _ReflectionColor.rgb;
            float4 diffuseColor = tex2D(_DiffuseMap, input.uv_DiffuseMap) * _DiffuseColor;
            float3 finalColor = lerp(lerp(_BaseColor.rgb, diffuseColor.rgb, diffuseColor.a), reflectionColor, _ReflectionStrength);

            float3 detailMask = tex2D(_DetailMap, input.uv_DetailMap).rgb;
            float3 detailColor = lerp(_DetailColor.rgb, finalColor, detailMask);
            finalColor = lerp(detailColor, finalColor, saturate(input.depth * _DetailMapDepthBias));

            output.Albedo = finalColor;
            output.Alpha = _BaseColor.a;
        }

        void VertexMain(inout appdata_full input, out Input output)
        {
            UNITY_INITIALIZE_OUTPUT(Input, output);
            output.depth = UnityObjectToClipPos(input.vertex).z;
        }
        ENDCG
          
            Pass{
            Name "Cutout"
            AlphaTest Greater 0.9
            SetTexture[_Cutout]{

        }
        }
    }

    FallBack "VertexLit"
}
2

You don’t need another pass for this. Just set your alpha texture and clip directly in the first pass.

3

The problem is I am new to shaders and wouldn’t even know where to start. I have added a pass before to add a decal, but this is different.

4

Look for alphatest in the surface shader documentation.

5

Thanks, I found a Unity answers post that helped me:

6

How can I do this with URP?

7

Blend One Zero
AlphaToMask On

1 Like
8

Old post but:

Tags
{
    "Queue" = "AlphaTest"
}
Pass
{
//...
half4 frag(fragIn fragIn) : SV_Target
{
      //...
      if (alpha < _Cutoff) discard;
      //...
      return color;
}