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Unity-Shader(三)高光反射&Blinn-Ph

Unity-Shader(三)高光反射&Blinn-Ph

作者: 7fc14ada7795 | 来源:发表于2018-09-03 15:18 被阅读2次

先看一下基本光照模型中的高光反射部分的计算公式:

image

逐顶点光照实现 高光反射

分析

在Properties语义块中声明了三个属性:

Properties
{
    _Diffuse ("Diffuse" , Color) = (1,1,1,1)
    _Specular ("Specular" , Color) = (1,1,1,1)
    _Gloss ("Gloss" , Range(8.0,256)) = 20
}

_Specular用来控制材质的高光反射的颜色

_Gloss用于控制高光区域的大小

其他的代码基本和往常一样,不细说了

Tags { "LightMode" = "ForwardBase" }

CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "Lighting.cginc"

fixed4 _Diffuse;
fixed4 _Specular;
float _Gloss;

struct a2v{
    float4 vertex : POSITION;
    float3 normal : NORMAL;
};
struct v2f{
    float4 pos : SV_POSITION;
    float3 color : COLOR;
};

在顶点着色器中计算了包含高光反射的光照模型

v2f vert(a2v v){
    v2f o;
    o.pos = UnityObjectToClipPos( v.vertex);
    //得到环境光
    fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
    //将法线从模型空间变换的世界空间
    fixed3 worldNormal = normalize(mul(v.normal , (float3x3)unity_WorldToObject));
    //在世界空间中光照方向
    fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
    fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal , worldLightDir));
    fixed3 reflectDir = normalize(reflect(-worldLightDir , worldNormal));
    fixed3 viewDir = normalize(_WorldSpaceCameraPos.xyz - mul(unity_ObjectToWorld , v.vertex).xyz);
    fixed3 specular = _LightColor0.rgb * _Specular.rgb *pow(saturate(dot(reflectDir , viewDir)),_Gloss);
    o.color = ambient + diffuse + specular;
    return o;
}

首先计算了入射光线防线关于表面法线的反射方向reflectDir。犹豫Cg的reflect函数的入社方向要求是由光源指向交点处的,因此需要对worldLightDir取反再传给reflect函数。

然后通过——WorldSpaceCameraPos得到世界空间中的摄像机位置,再把顶点位置从模型空间变换得到世界空间下,再通过——WorldSpaceCameraPos相减即可得到世界空间下的视角方向。

最后

fixed4 frag(v2f i) : SV_Target{
    return fixed4(i.color , 1.0);
}

效果

image

使用逐顶点着色器的方法得到的高光效果有比较大的问题,可以从效果图中看到有明显的不平滑,因为高光反射部分的计算是非线性的,而在顶点着色器中计算光照在进行插值的过程是线性的,破换了原计算的非线性关系。

代码

// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'
// Upgrade NOTE: replaced '_World2Object' with 'unity_WorldToObject'
// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "Unlit/Specular_1"
{
    Properties
    {
        _Diffuse ("Diffuse" , Color) = (1,1,1,1)
        _Specular ("Specular" , Color) = (1,1,1,1)
        _Gloss ("Gloss" , Range(8.0,256)) = 20
    }
    SubShader
    {
        Pass{
            Tags { "LightMode" = "ForwardBase" }

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "Lighting.cginc"

            fixed4 _Diffuse;
            fixed4 _Specular;
            float _Gloss;

            struct a2v{
                float4 vertex : POSITION;
                float3 normal : NORMAL;
            };
            struct v2f{
                float4 pos : SV_POSITION;
                float3 color : COLOR;
            };

            v2f vert(a2v v){
                v2f o;
                o.pos = UnityObjectToClipPos( v.vertex);
                fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
                fixed3 worldNormal = normalize(mul(v.normal , (float3x3)unity_WorldToObject));
                fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
                fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal , worldLightDir));
                fixed3 reflectDir = normalize(reflect(-worldLightDir , worldNormal));
                fixed3 viewDir = normalize(_WorldSpaceCameraPos.xyz - mul(unity_ObjectToWorld , v.vertex).xyz);
                fixed3 specular = _LightColor0.rgb * _Specular.rgb *pow(saturate(dot(reflectDir , viewDir)),_Gloss);
                o.color = ambient + diffuse + specular;
                return o;
            }

            fixed4 frag(v2f i) : SV_Target{
                return fixed4(i.color , 1.0);
            }


            ENDCG
        }
        
    }
    Fallback "Specular"
}

逐像素 实现高光反射模型

分析

在原来代码的基础上进行修改

修改顶点着色器的输出结构v2f

struct v2f{
    float4 pos : SV_POSITION;
    float3 worldNormal : TEXCOORD0;
    float3 worldPos : TEXCOORD1;
};

修改顶点着色器

v2f vert(a2v v){
    v2f o;
    o.pos = UnityObjectToClipPos( v.vertex);
    o.worldNormal = mul(v.normal , (float3x3)unity_WorldToObject);
    o.worldPos = mul(unity_ObjectToWorld , v.vertex).xyz;
    return o;
}

修改片元着色器:

fixed4 frag(v2f i) : SV_Target{
    fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
    fixed3 worldNormal = normalize(i.worldNormal);
    fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
    fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal , worldLightDir));
    fixed3 reflectDir = normalize(reflect(-worldLightDir , worldNormal));
    fixed3 viewDir = normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);
    fixed3 specular = _LightColor0.rgb * _Specular.rgb * pow(saturate(dot(reflectDir , viewDir)) , _Gloss);
    return fixed4(ambient + diffuse + specular , 1.0);
}

效果:

image

可以看出,使用逐像素实现高光反射,使得高光效果更加平滑

全部代码:

// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'
// Upgrade NOTE: replaced '_World2Object' with 'unity_WorldToObject'
// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "Unlit/Specular_2"
{
    Properties
    {
        _Diffuse ("Diffuse" , Color) = (1,1,1,1)
        _Specular ("Specular" , Color) = (1,1,1,1)
        _Gloss ("Gloss" , Range(8.0,256)) = 20
    }
    SubShader
    {
        Pass{
            Tags { "LightMode" = "ForwardBase" }

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "Lighting.cginc"

            fixed4 _Diffuse;
            fixed4 _Specular;
            float _Gloss;

            struct a2v{
                float4 vertex : POSITION;
                float3 normal : NORMAL;
            };
            struct v2f{
                float4 pos : SV_POSITION;
                float3 worldNormal : TEXCOORD0;
                float3 worldPos : TEXCOORD1;
            };

            v2f vert(a2v v){
                v2f o;
                o.pos = UnityObjectToClipPos( v.vertex);
                o.worldNormal = mul(v.normal , (float3x3)unity_WorldToObject);
                o.worldPos = mul(unity_ObjectToWorld , v.vertex).xyz;
                return o;
            }

            fixed4 frag(v2f i) : SV_Target{
                fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
                fixed3 worldNormal = normalize(i.worldNormal);
                fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
                fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal , worldLightDir));
                fixed3 reflectDir = normalize(reflect(-worldLightDir , worldNormal));
                fixed3 viewDir = normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);
                fixed3 specular = _LightColor0.rgb * _Specular.rgb * pow(saturate(dot(reflectDir , viewDir)) , _Gloss);
                return fixed4(ambient + diffuse + specular , 1.0);
            }


            ENDCG
        }
        
    }
    Fallback "Specular"
}

Blinn-Phong 光照模型

公式:

image

修改逐像素实现高光反射的片元着色器的代码:

fixed4 frag(v2f i) : SV_Target{
    fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
    fixed3 worldNormal = normalize(i.worldNormal);
    fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
    fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal , worldLightDir));
    fixed3 reflectDir = normalize(reflect(-worldLightDir , worldNormal));
    fixed3 viewDir = normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);
    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);
}

效果:

image

全部代码

// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'
// Upgrade NOTE: replaced '_World2Object' with 'unity_WorldToObject'
// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "Unlit/Specular_3"
{
    Properties
    {
        _Diffuse ("Diffuse" , Color) = (1,1,1,1)
        _Specular ("Specular" , Color) = (1,1,1,1)
        _Gloss ("Gloss" , Range(8.0,256)) = 20
    }
    SubShader
    {
        Pass{
            Tags { "LightMode" = "ForwardBase" }

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "Lighting.cginc"

            fixed4 _Diffuse;
            fixed4 _Specular;
            float _Gloss;

            struct a2v{
                float4 vertex : POSITION;
                float3 normal : NORMAL;
            };
            struct v2f{
                float4 pos : SV_POSITION;
                float3 worldNormal : TEXCOORD0;
                float3 worldPos : TEXCOORD1;
            };

            v2f vert(a2v v){
                v2f o;
                o.pos = UnityObjectToClipPos( v.vertex);
                o.worldNormal = mul(v.normal , (float3x3)unity_WorldToObject);
                o.worldPos = mul(unity_ObjectToWorld , v.vertex).xyz;
                return o;
            }

            fixed4 frag(v2f i) : SV_Target{
                fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
                fixed3 worldNormal = normalize(i.worldNormal);
                fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
                fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal , worldLightDir));
                fixed3 reflectDir = normalize(reflect(-worldLightDir , worldNormal));
                fixed3 viewDir = normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);
                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"
}

最后

三种类型高光反射的效果对比
从左到右分别是 逐顶点高光反射、逐像素高光反射、Blinn-Phong光照模型

image

可以看出,Blinn-Phong模型的高光反射部分看起来更大更亮,在实际渲染中,绝大多数情况也都会选择Blinn-Phong光照模型

划重点

使用 normalize(_WorldSpaceLightPos0.xyz);来得到光源方向

使用 normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);来得到视角方向

本文所写内容参考《UnityShader 入门精要》。

原文地址 : Kelo'Blog

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