unity 渐变纹理

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纹理可以存储任何表面属性，一种常见的办法就是使用渐变纹理来控制漫反射光照的颜色。

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Shader "My/RampTexture"{
    Properties{
		_Color("Color Tint", Color) = (1,1,1,1)
        _RampTex("Ramp Tex", 2D) = "white" {}
        _Specular("Specular", Color) = (1,1,1,1)
        _Gloss("Gloss", Range(8, 256)) = 20
    }
    
    SubShader{
        Pass{
            Tags{"LightMode"="ForwardBase"}
            CGPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #include "Lighting.cginc"
                fixed4 _Color;
            	sampler2D _RampTex;
            	float4 _RampTex_ST;
            	fixed4 _Specular;
            	float  _Gloss;
            	
            struct a2v{
                float4 vertex      : POSITION;
                float3 normal      : NORMAL;
                float4 texcoord    : TEXCOORD0;
            };
            
            struct v2f{
              float4 pos          : SV_POSITION;
              float3 worldNormal  : TEXCOORD0;
              float3 worldPos	  : TEXCOORD1;
              float2 uv			  : TEXCOORD2;
            };
            
            v2f vert(a2v v){
                v2f o;
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                o.worldNormal = UnityObjectToWorldNormal(v.normal);
                o.worldPos = mul(_Object2World, v.vertex).xyz;
                o.uv = TRANSFORM_TEX(v.texcoord, _RampTex);
                return o;
            }
            
            fixed4 frag(v2f i) : SV_Target{
                fixed3 worldNormal = normalize(i.worldNormal);
                fixed3 worldLightDir    = normalize(UnityWorldSpaceLightDir(i.worldPos));
                fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
                fixed3 halfLambert = 0.5* dot(worldNormal, worldLightDir) + 0.5;
                fixed3 diffuseColor = tex2D(_RampTex, fixed2(halfLambert, halfLambert)).rgb * _Color.rgb;  //使用半兰伯特模型来构建一个纹理坐标，并用这个坐标对渐变纹理采样
                fixed3 diffuse = _LightColor0.rgb * diffuseColor;
                fixed3 viewDir = normalize(UnityWorldSpaceViewDir(i.worldPos));
                fixed3 halfDir = normalize(worldLightDir + viewDir);
                fixed3 specular = _LightColor0.rgb * _Specular.rgb * pow(max(0, dot(worldNormal, halfDir)) ,_Gloss);
            }
            
            return fixed4(ambient + diffuse + specular, 1.0);
            
            ENDCG
        }
    }
    Fallback "Specular"
}