Custom shader fundamentals in Unity

Introduction

Custom shaders let you control how objects look in a game. They help create special effects like shiny surfaces or glowing lights.

You want to make a character's skin look shiny or wet.

You need a glowing effect on a magic item.

You want to create a cartoon or stylized look for your game.

You want to add special lighting that Unity's built-in shaders don't have.

You want to optimize graphics by writing simple shaders for specific effects.

Syntax

Unity

Shader "Custom/ExampleShader" {
  Properties {
    _Color ("Color", Color) = (1,1,1,1)
  }
  SubShader {
    Pass {
      CGPROGRAM
      #pragma vertex vert
      #pragma fragment frag

      struct appdata {
        float4 vertex : POSITION;
      };

      struct v2f {
        float4 pos : SV_POSITION;
      };

      fixed4 _Color;

      v2f vert (appdata v) {
        v2f o;
        o.pos = UnityObjectToClipPos(v.vertex);
        return o;
      }

      fixed4 frag (v2f i) : SV_Target {
        return _Color;
      }
      ENDCG
    }
  }
}

The Properties block defines inputs you can change in the editor.

The SubShader contains the actual code that runs on the GPU.

Examples

This shader colors everything red by default.

Unity

Shader "Custom/SimpleColor" {
  Properties {
    _Color ("Color", Color) = (1,0,0,1)
  }
  SubShader {
    Pass {
      CGPROGRAM
      #pragma vertex vert
      #pragma fragment frag

      struct appdata { float4 vertex : POSITION; };
      struct v2f { float4 pos : SV_POSITION; };

      fixed4 _Color;

      v2f vert(appdata v) {
        v2f o;
        o.pos = UnityObjectToClipPos(v.vertex);
        return o;
      }

      fixed4 frag(v2f i) : SV_Target {
        return _Color;
      }
      ENDCG
    }
  }
}

This shader applies a texture image to the object.

Unity

Shader "Custom/TextureShader" {
  Properties {
    _MainTex ("Texture", 2D) = "white" {}
  }
  SubShader {
    Pass {
      CGPROGRAM
      #pragma vertex vert
      #pragma fragment frag

      sampler2D _MainTex;
      struct appdata {
        float4 vertex : POSITION;
        float2 uv : TEXCOORD0;
      };
      struct v2f {
        float4 pos : SV_POSITION;
        float2 uv : TEXCOORD0;
      };

      v2f vert(appdata v) {
        v2f o;
        o.pos = UnityObjectToClipPos(v.vertex);
        o.uv = v.uv;
        return o;
      }

      fixed4 frag(v2f i) : SV_Target {
        return tex2D(_MainTex, i.uv);
      }
      ENDCG
    }
  }
}

Sample Program

This shader colors any object with a blue color by default. You can change the color in the Unity editor. It uses a simple vertex and fragment program to set the color.

Unity

Shader "Custom/BasicColorShader" {
  Properties {
    _Color ("Color", Color) = (0, 0.5, 1, 1)
  }
  SubShader {
    Tags { "RenderType"="Opaque" }
    Pass {
      CGPROGRAM
      #pragma vertex vert
      #pragma fragment frag

      struct appdata {
        float4 vertex : POSITION;
      };

      struct v2f {
        float4 pos : SV_POSITION;
      };

      fixed4 _Color;

      v2f vert(appdata v) {
        v2f o;
        o.pos = UnityObjectToClipPos(v.vertex);
        return o;
      }

      fixed4 frag(v2f i) : SV_Target {
        return _Color;
      }
      ENDCG
    }
  }
  FallBack "Diffuse"
}

Important Notes

Always test your shader on simple objects first to see how it looks.

Use the Unity editor's material inspector to tweak shader properties live.

Shaders run on the graphics card, so small mistakes can cause no rendering or errors.

Summary

Custom shaders let you control how objects look by writing small programs.

They use a Properties block for inputs and a SubShader block for GPU code.

Start simple, then add effects like textures or lighting step by step.