【Unity Shader】实现基础光照模型

ゞ浴缸里的玫瑰 2023-09-27 11:21 120阅读 0赞

**写在前面**

现在问你：什么是漫反射？什么是高光反射？Phong和BlinnPhong模型的区别在哪儿？漫反射有哪几个参数？高光反射有几个参数？公式分别是啥？计算出来的结果指的是什么？...如果这种超基础的理论知识都回答不上来的话，建议再去恶补一遍理论！！一切都搞清楚了再上手代码也不迟~！

**参考书籍**

仍旧是冯乐乐那本《Unity Shader 入门精要》

--------------------

## 1 实现漫反射光照模型 ##

### 1.1逐顶点光照：Shader代码 ###

Shader "Unity Shaders Book/Chapter 6/Diffuse Vertex-Level"
    {
        Properties
        {
            _Diffuse  ("Diffuse", Color) = (1, 1, 1, 1)
        }
        SubShader
        {
            Pass
            {
                Tags { "LightMode" = "ForwardBase" }
                CGPROGRAM
    
                #pragma vertex vert
                #pragma fragment frag
                #include "lighting.cginc"
    
                fixed4 _Diffuse;
    
                struct a2v {
                    float4 vertex : POSITION;
                    float3 normal : NORMAL;
                };
                
                struct v2f {
                    float4 pos : SV_POSITION;
                    fixed3 color : COLOR;
                };
    
                v2f vert(a2v v) {
                    v2f o; //定义返回值o
                    o.pos = UnityObjectToClipPos(v.vertex);  //顶点着色器的基本任务
                    fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;  //获得环境光
    
                    fixed3 worldNormal = normalize(mul(v.normal, (float3x3)unity_WorldToObject));  //法向量由物体->世界
                    fixed3 worldLight = normalize(_WorldSpaceLightPos0.xyz);
                    fixed3 diffuse = _Diffuse.rgb * _LightColor0.rgb * saturate(dot(worldNormal, worldLight));
                    o.color = diffuse + ambient;
    
                    return o;
                }
    
                fixed4 frag(v2f i) : SV_Target {
                    return fixed4(i.color, 1.0);
                }
                ENDCG
            }
        }
        FallBack  "Diffuse"
    }

效果会跟后面的逐像素光照模型一起放出来做一个对比。

### 1.2 逐像素光照：Shader代码 ###

Shader "Unity Shaders Book/Chapter 6/Diffuse Pixel-Level"
    {
        Properties
        {
            _Diffuse  ("Diffuse", Color) = (1, 1, 1, 1)
        }
        SubShader
        {
            Pass
            {
                Tags { "LightMode" = "ForwardBase" }
                CGPROGRAM
    
                #pragma vertex vert
                #pragma fragment frag
                #include "lighting.cginc"
    
                fixed4 _Diffuse;
    
                struct a2v {
                    float4 vertex : POSITION;
                    float3 normal : NORMAL;
                };
                //顶点着色器输出的
                struct v2f {
                    float4 pos : SV_POSITION;
                    float3 worldNormal : TEXCOORD0;  //自定义的一些参数就用texcoord0 
                };
    
                v2f vert(a2v v) {
                    v2f o; //定义返回值o
                    o.pos = UnityObjectToClipPos(v.vertex);  //顶点着色器的基本任务
                    o.worldNormal = mul(v.normal, (float3x3)unity_WorldToObject);  //就传递一个世界空间的发现就行了
                    return o;
                }
    
                fixed4 frag(v2f i) : SV_Target {
                    fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;  //获得环境光
                    fixed3 worldNormal = normalize(i.worldNormal);  //法向量由物体->世界
                    fixed3 worldLight = normalize(_WorldSpaceLightPos0.xyz);
                    fixed3 diffuse = _Diffuse.rgb * _LightColor0.rgb * saturate(dot(worldNormal, worldLight));
                    fixed3 color = diffuse + ambient;
    
                    return fixed4(color, 1.0);
                }
                ENDCG
            }
        }
        FallBack  "Diffuse"
    }

### 1.3 半兰伯特模型：Shader代码 ###

简单谈一谈**半兰伯特（Half Lambert）光照模型**为什么会被提出来？

兰伯特（Lambert）光照模型使用了max把法向量和指向光源方向的向量点积限制在了\[0, 1\]之间，这样做就会导致原本为负的区域直接给全部映射到了0，这就意味着背面光的效果直接没有了！

而半兰伯特做了一个这样的操作，就像之前做法线\[-1, 1\]->像素颜色值\[0, 1\]映射的做法一样，它把原始点积结果映射到了\[0, 1\]上，那么背面光不就也有个缓慢过渡的效果了！但我们需要明白，半兰伯特是没有任何物理依据的，只是为了加强视觉效果而提出的一个方法而已。

Shader "Unity Shaders Book/Chapter 6/Diffuse HalfLambert"
    {
        Properties
        {
            _Diffuse  ("Diffuse", Color) = (1, 1, 1, 1)
        }
        SubShader
        {
            Pass
            {
                Tags { "LightMode" = "ForwardBase" }
                CGPROGRAM
    
                #pragma vertex vert
                #pragma fragment frag
                #include "lighting.cginc"
    
                fixed4 _Diffuse;
    
                struct a2v {
                    float4 vertex : POSITION;
                    float3 normal : NORMAL;
                };
                //顶点着色器输出的
                struct v2f {
                    float4 pos : SV_POSITION;
                    float3 worldNormal : TEXCOORD0;  //自定义的一些参数就用texcoord0 
                };
    
                v2f vert(a2v v) {
                    v2f o; //定义返回值o
                    o.pos = UnityObjectToClipPos(v.vertex);  //顶点着色器的基本任务
                    o.worldNormal = mul(v.normal, (float3x3)unity_WorldToObject);  //就传递一个世界空间的发现就行了
                    return o;
                }
    
                fixed4 frag(v2f i) : SV_Target {
                    fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;  //获得环境光
                    fixed3 worldNormal = normalize(i.worldNormal);  //法向量由物体->世界
                    fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
    
                    //computer diffuse
                    fixed halfLambert = dot(worldNormal, worldLightDir) * 0.5 + 0.5;
                    fixed3 diffuse = _Diffuse.rgb * _LightColor0.rgb * halfLambert;
                    fixed3 color = diffuse + ambient;
    
                    return fixed4(color, 1.0);
                }
                ENDCG
            }
        }
        FallBack  "Diffuse"
    }

### 1.4 三者效果动态对比 ###

#### 1.4.1 逐顶点和逐像素的对比 ####

这里我直接做了一个动图，左边是逐顶点，右边是逐像素，效果可能不是特别明显但凑合，大概可以看得出来左边变化的会有锯齿一样的不匀称的感觉，而右边相对来说就很平滑：

![cdff4acad58d48b0afe150175955c861.gif][]

#### 1.4.2 逐像素和半兰伯特的对比 ####

二者对比如下：可以看到左边的逐像素不如右边的过渡效果好，右边有个背光过渡的感觉。

![3783dd0d104343279644710294d87dca.gif][]

## 2 实现高光反射光照模型 ##

### 2.1 逐顶点光照：Shader代码 ###

// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'
    
    
    Shader "Unity Shaders Book/Chapter 6/Specular Vertex-Level"
    {
        Properties
        {
            _Diffuse ("Diffuse", Color) = (1, 1, 1, 1)
            _Specular("Specular", Color) = (1, 1, 1, 1)
            _Gloss("Gloss", Range(8.0, 256)) = 20  //这是高光项
        }
        SubShader 
        {
            Pass 
            {
                Tags { "LightMode" = "ForwardBase" }
                CGPROGRAM
                
                #pragma vertex vert
                #pragma fragment frag
                #include "lighting.cginc"
    
                //properties
                fixed4 _Diffuse;
                fixed4 _Specular;
                float _Gloss;
    
                struct a2v {
                    float4 vertex : POSITION;
                    float3 normal : NORMAL;
                };
                
                struct v2f {
                    float4 pos : SV_POSITION;
                    fixed3 color : COLOR;
                };
    
                //逐顶点基本在顶点着色器中实现
                v2f vert(a2v v) {
                    v2f o;
                    //pos2clip space
                    o.pos = UnityObjectToClipPos(v.vertex);
                    //ambient
                    fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
                    //normal:object -> world & normalize
                    fixed3 worldNormal = normalize(mul(v.normal, (float3x3)unity_WorldToObject));
                    //lightDir
                    fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
                    //reflectDir
                    fixed3 reflectDir = normalize(reflect(-worldLightDir, worldNormal));
                    //viewDir =camera.pos - vertex.pos 
                    fixed3 viewDir = normalize(_WorldSpaceCameraPos.xyz - mul(unity_ObjectToWorld, v.vertex).xyz);
    
                    //the diffuse:
                    fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal, worldLightDir));
    
                    //the specular:
                    fixed3 specular = _LightColor0.rgb * _Specular.rgb * pow(saturate(dot(reflectDir, viewDir)), _Gloss);
    
                    //all:
                    o.color = diffuse + specular + ambient;
                    return o;
                }
    
                fixed4 frag(v2f i) : SV_Target {
                    return fixed4(i.color, 1.0);
                }
                ENDCG
            }
        }
        FallBack  "Specular"
    }

### 2.2 逐像素光照：Shader代码 ###

// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'
    // Upgrade NOTE: replaced '_World2Object' with 'unity_WorldToObject'
    
    Shader "Unity Shaders Book/Chapter 6/Specular Pixel-Level"
    {
        Properties
        {
            _Diffuse ("Diffuse", Color) = (1, 1, 1, 1)
            _Specular("Specular", Color) = (1, 1, 1, 1)
            _Gloss("Gloss", Range(8.0, 256)) = 20  //这是高光项
        }
        SubShader 
        {
            Pass 
            {
                Tags { "LightMode" = "ForwardBase" }
                CGPROGRAM
                
                #pragma vertex vert
                #pragma fragment frag
                #include "lighting.cginc"
    
                //properties
                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;
                    //pos2clip space
                    o.pos = UnityObjectToClipPos(v.vertex);
                    //worldnormal
                    o.worldNormal = mul(v.normal, (float3x3)unity_WorldToObject);
                    //worldPos
                    o.worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
    
                    return o;
                }
    
                fixed4 frag(v2f i) : SV_Target {
                    //ambient
                    fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
                    //lightDir
                    fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
                    //worldNormal
                    fixed3 worldNormal = normalize(i.worldNormal);
                    //viewDir
                    fixed3 viewDir = normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);
                    //reflectDir
                    fixed3 reflectDir = normalize(reflect(-worldLightDir, worldNormal));
    
                    fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(i.worldNormal, worldLightDir));
                    
                    fixed3 specular = _LightColor0 * _Specular * pow(saturate(dot(viewDir, reflectDir)), _Gloss);
    
                    //plus 3:
                    fixed3 color = specular + ambient + diffuse;
    
                    return fixed4(color, 1.0);
                }
                ENDCG
            }
        }
        FallBack  "Specular"
    }

### 2.3 二者动态效果对比 ###

我就简单录了个随着光照方向改变，逐顶点（左）和逐像素（右）的高光区域的变化，可以很明显看到左边是有锯齿的感觉的，右边明显顺滑很多！

![7703c16394c34e0f9b1831aaa31a56ff.gif][]

## 3 实现Blinn-Phong光照模型 ##

Blinn-Phong就是在2.3中实现的逐像素（高光+漫反射+环境光）的基础上，把高光项的max()里的viewDir和LightDir替换成了更易计算的halfDir和normal向量，相比于Phong计算的更加快了。

### 3.1 Shader代码 ###

Shader "Unity Shaders Book/Chapter 6/BlinnPhong"
    {
        Properties
        {
            _Diffuse ("Diffuse", Color) = (1, 1, 1, 1)
            _Specular("Specular", Color) = (1, 1, 1, 1)
            _Gloss("Gloss", Range(8.0, 256)) = 20  //这是高光项
        }
        SubShader 
        {
            Pass 
            {
                Tags { "LightMode" = "ForwardBase" }
                CGPROGRAM
                
                #pragma vertex vert
                #pragma fragment frag
                #include "lighting.cginc"
    
                //properties
                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;
                    //pos2clip space
                    o.pos = UnityObjectToClipPos(v.vertex);
                    //worldnormal
                    o.worldNormal = mul(v.normal, (float3x3)unity_WorldToObject);
                    //IF using UnityObjectToWorldNormal:
                    //o.worldNormal = UnityObjectToWorldNormal(v.normal);
                    
                    //worldPos
                    o.worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
    
                    return o;
                }
    
                fixed4 frag(v2f i) : SV_Target {
                    //ambient
                    fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
                    //lightDir
                    fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
                    //IF using UnityWorldSpaceLightDir:
                    //fixed3 worldLightDir = normalize(UnityWorldSpaceLightDir(i.worldPos));
                    
                    //worldNormal
                    fixed3 worldNormal = normalize(i.worldNormal);
                    
                    //viewDir
                    fixed3 viewDir = normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);
                    //IF using UnityWorldSpaceViewDir:
                    //fixed3 viewDir = normalize(UnityWorldSpaceViewDir(i.worldPos));
    
                    // //reflectDir
                    // fixed3 reflectDir = normalize(reflect(-worldLightDir, worldNormal));
                    // h:
                    fixed3 hDir = normalize(viewDir + worldLightDir);
    
                    fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(i.worldNormal, worldLightDir));
                    
                    fixed3 specular = _LightColor0 * _Specular * pow(saturate(dot(worldNormal, hDir)), _Gloss);
    
                    //plus 3:
                    fixed3 color = specular + ambient + diffuse;
    
                    return fixed4(color, 1.0);
                }
                ENDCG
            }
        }
        FallBack  "Specular"
    }

### 3.2 Blinn-Phong与Phong效果对比 ###

可以看到Blinn-Phong（右）的高光范围比Phong（左）的更大、更亮一些，实际渲染中也多选择Blinn-Phong模型来计算。

![185a682b7b554a4eb7a08ba4069e0d76.gif][]

[cdff4acad58d48b0afe150175955c861.gif]: https://img-blog.csdnimg.cn/cdff4acad58d48b0afe150175955c861.gif
[3783dd0d104343279644710294d87dca.gif]: https://img-blog.csdnimg.cn/3783dd0d104343279644710294d87dca.gif
[7703c16394c34e0f9b1831aaa31a56ff.gif]: https://img-blog.csdnimg.cn/7703c16394c34e0f9b1831aaa31a56ff.gif
[185a682b7b554a4eb7a08ba4069e0d76.gif]: https://img-blog.csdnimg.cn/185a682b7b554a4eb7a08ba4069e0d76.gif