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"
}