Unity Shader——Writing Surface Shaders(3)——Surface Shader Lighting Examples

Surface Shader 光照例子

　　这里有一些自定义光照模型和Surface Shaders的例子。通常的Surface Shader例子在这里。

　　由于延迟光照在某些自定义的逐材质光照模型中表现得并不好，在下面大多数例子中，我们让shader只编译到正向渲染中。

漫反射（Diffuse）

　　让我们以使用内建Lambert光照模型的shader作为开始吧！

Shader "Example/Diffuse Texture" {
    Properties {
      _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader {
      Tags { "RenderType" = "Opaque" }
      CGPROGRAM
      #pragma surface surf Lambert
      
      struct Input {
          float2 uv_MainTex;
      };
      
      sampler2D _MainTex;
      
      void surf (Input IN, inout SurfaceOutput o) {
          o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
      }
      ENDCG
    }
    Fallback "Diffuse"
  }

　　下面是使用一张纹理贴图和不使用一张真实的纹理贴图的样子（此场景中有一个方向光）

 

　　现在，我们来做个完全一样的，但是使用我们自己的光照模型，而不是内建Lambert光照模型。Surface Shader光照模型仅是一些我们需要编写的函数。这里有一个简单的Lambert光照模型。注意到只有CGPROGRAM部分发生了改变，周边的shader代码是完全一样的：

Shader "Example/Diffuse Texture" {
        Properties {
            _MainTex ("Texture", 2D) = "white" {}
        }
        SubShader {
        Tags { "RenderType" = "Opaque" }
        CGPROGRAM
          #pragma surface surf SimpleLambert
  
          half4 LightingSimpleLambert (SurfaceOutput s, half3 lightDir, half atten) {
              half NdotL = dot (s.Normal, lightDir);
              half4 c;
              c.rgb = s.Albedo * _LightColor0.rgb * (NdotL * atten * 2);
              c.a = s.Alpha;
              return c;
          }
  
        struct Input {
            float2 uv_MainTex;
        };
        
        sampler2D _MainTex;
        
        void surf (Input IN, inout SurfaceOutput o) {
            o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
        }
        ENDCG
        }
        Fallback "Diffuse"
    }

　　所以我们的简单漫反射光照模型就是LightingSimpleLambert 函数。它通过计算表面法线和光线方向的点积来计算光照，然后应用光照衰减和颜色。

环绕漫反射（Diffuse Wrap）

　　这里是环绕漫反射——漫反射光照的修改版，即照明环绕在物体的边缘。它对用来仿照次表面散射效果很有用。因为只是CGPROGRAM 部分发生了改变，老生常谈一次，周边的shader代码就省略了：

 ...ShaderLab code...
    CGPROGRAM
    #pragma surface surf WrapLambert

    half4 LightingWrapLambert (SurfaceOutput s, half3 lightDir, half atten) {
        half NdotL = dot (s.Normal, lightDir);
        half diff = NdotL * 0.5 + 0.5;
        half4 c;
        c.rgb = s.Albedo * _LightColor0.rgb * (diff * atten * 2);
        c.a = s.Alpha;
        return c;
    }

    struct Input {
        float2 uv_MainTex;
    };
    
    sampler2D _MainTex;
        void surf (Input IN, inout SurfaceOutput o) {
        o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
    }
    ENDCG
    ...ShaderLab code...

 

卡通渐变（Toon Ramp）

　　下面是一个"渐变(Ramp)"光照模型。它使用一张渐变纹理来定义表面怎样对光线和法线的夹角做出反应。这能用来实现多种效果，包括卡通光照。

...ShaderLab code...
    CGPROGRAM
    #pragma surface surf Ramp

    sampler2D _Ramp;

    half4 LightingRamp (SurfaceOutput s, half3 lightDir, half atten) {
        half NdotL = dot (s.Normal, lightDir);
        half diff = NdotL * 0.5 + 0.5;
        half3 ramp = tex2D (_Ramp, float2(diff)).rgb;
        half4 c;
        c.rgb = s.Albedo * _LightColor0.rgb * ramp * (atten * 2);
        c.a = s.Alpha;
        return c;
    }

    struct Input {
        float2 uv_MainTex;
    };
    
    sampler2D _MainTex;
    
    void surf (Input IN, inout SurfaceOutput o) {
        o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
    }
    ENDCG
    ...ShaderLab code...

 

简单镜面（Simple Specular）

　　下面是一个简单镜面光照模型。这对于内置的BlinnPhong实际所做的内容来说非常简单。我们把它放在这来说明它是如何工作的。

  ...ShaderLab code...
    CGPROGRAM
    #pragma surface surf SimpleSpecular

    half4 LightingSimpleSpecular (SurfaceOutput s, half3 lightDir, half3 viewDir, half atten) {
        half3 h = normalize (lightDir + viewDir);

        half diff = max (0, dot (s.Normal, lightDir));

        float nh = max (0, dot (s.Normal, h));
        float spec = pow (nh, 48.0);

        half4 c;
        c.rgb = (s.Albedo * _LightColor0.rgb * diff + _LightColor0.rgb * spec) * (atten * 2);
        c.a = s.Alpha;
        return c;
    }

    struct Input {
        float2 uv_MainTex;
    };
    
    sampler2D _MainTex;
    
    void surf (Input IN, inout SurfaceOutput o) {
        o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
    }
    ENDCG
    ...ShaderLab code...

解码光照贴图（Decoding Lightmaps）

　　我们将以这样一个shader作为开始：它模仿内置的光照贴图解码工作，使用Unity自带的DecodeLightmap函数解码lightmap中储存的数据信息，以及使用自带的UNITY_DIRBASIS宏定义方向光照贴图（Directional lightmap）的基本向量： 

 Shader "Example/Standard Lightmap Decoding" {
        Properties {
            _MainTex ("Texture", 2D) = "white" {}
        }
        SubShader {
            Tags { "RenderType" = "Opaque" }
            CGPROGRAM

            #pragma surface surf Standard

            half4 LightingStandard (SurfaceOutput s, half3 lightDir, half atten) {
                half NdotL = dot (s.Normal, lightDir);
                half4 c; c.rgb = s.Albedo * _LightColor0.rgb * (NdotL * atten * 2);
                c.a = s.Alpha;
                return c;
            }

            inline fixed4 LightingStandard_SingleLightmap (SurfaceOutput s, fixed4 color) {
                half3 lm = DecodeLightmap (color);
                return fixed4(lm, 0);
            }

            inline fixed4 LightingStandard_DualLightmap (SurfaceOutput s, fixed4 totalColor, fixed4 indirectOnlyColor, half indirectFade) {
                half3 lm = lerp (DecodeLightmap (indirectOnlyColor), DecodeLightmap (totalColor), indirectFade);
                return fixed4(lm, 0);
            }

            inline fixed4 LightingStandard_StandardLightmap (SurfaceOutput s, fixed4 color, fixed4 scale, bool surfFuncWritesNormal) {
                UNITY_DIRBASIS

                half3 lm = DecodeLightmap (color);
                half3 scalePerBasisVector = DecodeLightmap (scale);

                if (surfFuncWritesNormal)
                {
                    half3 normalInRnmBasis = saturate (mul (unity_DirBasis, s.Normal));
                    lm *= dot (normalInRnmBasis, scalePerBasisVector);
                }

                return fixed4(lm, 0);
            }

            struct Input {
                float2 uv_MainTex;
            };
            
            sampler2D _MainTex;
            
            void surf (Input IN, inout SurfaceOutput o) {
                o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
            }
            ENDCG
            }
        Fallback "Diffuse"
    }

　　现在，让我们为光照贴图中储存的光添加些色调映射（tone mapping）:

Shader "Example/Tonemapped Lightmap Decoding" {
        Properties {
            _MainTex ("Texture", 2D) = "white" {}
            _Gain ("Lightmap tone-mapping Gain", Float) = 1
            _Knee ("Lightmap tone-mapping Knee", Float) = 0.5
            _Compress ("Lightmap tone-mapping Compress", Float) = 0.33
        }
        SubShader {
            Tags { "RenderType" = "Opaque" }
            CGPROGRAM

            #pragma surface surf Tonemapped

            half4 LightingTonemapped (SurfaceOutput s, half3 lightDir, half atten) {
                half NdotL = dot (s.Normal, lightDir);
                half4 c; c.rgb = s.Albedo * _LightColor0.rgb * (NdotL * atten * 2); c.a = s.Alpha;
                return c;
            }

            half _Gain;
            half _Knee;
            half _Compress;
            
            inline half3 TonemapLight (half3 i) {
                i *= _Gain;
                return (i > _Knee)? (((i - _Knee)*_Compress)+_Knee): i;
            }

            inline fixed4 LightingTonemapped_SingleLightmap (SurfaceOutput s, fixed4 color) {
                half3 lm = TonemapLight(DecodeLightmap (color));
                return fixed4(lm, 0);
            }

            inline fixed4 LightingTonemapped_DualLightmap (SurfaceOutput s, fixed4 totalColor, fixed4 indirectOnlyColor, half indirectFade) {
                half3 lm = TonemapLight(lerp (DecodeLightmap (indirectOnlyColor), DecodeLightmap (totalColor), indirectFade));
                return fixed4(lm, 0);
            }

            inline fixed4 LightingTonemapped_StandardLightmap (SurfaceOutput s, fixed4 color, fixed4 scale, bool surfFuncWritesNormal) {
                UNITY_DIRBASIS

                half3 lm = TonemapLight(DecodeLightmap (color));
                half3 scalePerBasisVector = DecodeLightmap (scale);

                if (surfFuncWritesNormal)
                {
                    half3 normalInRnmBasis = saturate (mul (unity_DirBasis, s.Normal));
                    lm *= dot (normalInRnmBasis, scalePerBasisVector);
                }

                return fixed4(lm, 0);
            }

            struct Input {
                float2 uv_MainTex;
            };
            
            sampler2D _MainTex;
            
            void surf (Input IN, inout SurfaceOutput o) {
                o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
            }
            ENDCG
        }
        Fallback "Diffuse"
    }