UnityShader案例（七）——遮罩纹理

一、使用遮罩纹理的一般流程

通过采样得到遮罩纹理的纹素值，然后使用其中某个（或某几个）通道的值（例如texel.r）来与某种表面属性进行相乘，这样该通道的值为0，时，可以保护表面而不受该属性的影响。

二、具体实现

Shader "Custom/Texture/MaskTexture"{    Properties    {        _Color("Main Color",Color)=(1,1,1,1)        _MainTex ("Texture", 2D) = "white" {}        _BumpMap("Normal Map",2D)="bump"{}        _BumpScale("Bump Scale",Float )=1.0        _SpecularMask("Specular Mask",2D)="white"{}        _SpecularScale("Specular Scale",Float)=1.0        _Specular("Specular",Color)=(1,1,1,1)        _Gloss("Gloss",Range(8.0,256))=20    }    SubShader    {        Tags { "RenderType"="Opaque" }        LOD 100        Pass        {            Tags{"LightMode"="ForwardBase"}            CGPROGRAM            #pragma vertex vert            #pragma fragment frag            #include "UnityCG.cginc"            #include "Lighting.cginc"            fixed4 _Color;            sampler2D _MainTex;            float4 _MainTex_ST;            sampler2D _BumpMap;            float _BumpScale;            sampler2D _SpecularMask;            float _SpecularScale;            fixed4 _Specular;            float _Gloss;            struct appdata            {                float4 vertex : POSITION;                float3 normal:NORMAL;                float4 tangent:TANGENT;                float4 uv : TEXCOORD0;            };            struct v2f            {                float2 uv : TEXCOORD0;                float4 vertex : SV_POSITION;                float3 lightDir:TEXCOORD1;                float3 viewDir:TEXCOORD2;            };            v2f vert (appdata v)            {                v2f o;                o.vertex = UnityObjectToClipPos(v.vertex);                o.uv = TRANSFORM_TEX(v.uv, _MainTex);                TANGENT_SPACE_ROTATION;                o.lightDir=mul(rotation,ObjSpaceLightDir(v.vertex)).xyz;                o.viewDir=mul(rotation,ObjSpaceViewDir(v.vertex)).xyz;                return o;            }            fixed4 frag (v2f i) : SV_Target            {                fixed3 tangentLightDir=normalize(i.lightDir);                fixed3 tangentViewDir=normalize(i.viewDir);                fixed4 pcakedNormal=tex2D(_BumpMap,i.uv);                fixed3 tangentNormal;                tangentNormal=UnpackNormal(pcakedNormal);                tangentNormal.xy*=_BumpScale;                tangentNormal.z=sqrt(1.0-saturate(dot(tangentNormal.xy,tangentNormal.xy)));                fixed3 albedo=tex2D(_MainTex, i.uv).rgb*_Color.rgb;                fixed3 ambient=UNITY_LIGHTMODEL_AMBIENT.xyz*albedo;                fixed3 diffuse=_LightColor0.rgb * albedo*max(0,dot(tangentNormal,tangentLightDir));                fixed3 halfDir=normalize(tangentLightDir+tangentViewDir);                fixed3 specularMask=tex2D(_SpecularMask, i.uv).rgb*_SpecularScale;                fixed3 specular=_LightColor0.rgb*_Specular.rgb*pow(max(0,dot(tangentNormal,halfDir)),_Gloss)*specularMask;                return fixed4(ambient+diffuse+specular,1.0);            }            ENDCG        }    }}