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前言

我们在这篇文章中，实现法线贴图的正确采样

• Unity中Shader法线贴图（下）理论篇

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一、回顾一下上一篇中公式

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二、在Shader中实现

1.appdata中定义NORMAL与TANGENT语义.

half3 normal : NORMAL;
float4 tangent : TANGENT;

2.v2f中声明三个变量用于组成成切线空间下的旋转矩阵.

float3 tSpace0:TEXCOORD4;
float3 tSpace1:TEXCOORD5;
float3 tSpace2:TEXCOORD6;

3.在顶点着色器中执行:

• 切线从本地空间转化到世界空间

half3 worldTangent = UnityObjectToWorldDir(v.tangent);
//v.tangent.w:DCC软件中顶点UV值中的V值翻转情况.
//unity_WorldTransformParams.w:模型缩放是否有奇数负值.
half tangentSign = v.tangent.w * unity_WorldTransformParams.w;

- 由叉积计算出副切线

half3 worldBinormal = cross(worldNormal, worldTangent) * tangentSign;

• 得到 M^T

o.tSpace0 = float3(worldTangent.x,worldBinormal.x,worldNormal.x);
o.tSpace1 = float3(worldTangent.y,worldBinormal.y,worldNormal.y);
o.tSpace2 = float3(worldTangent.z,worldBinormal.z,worldNormal.z);

4.在片断着色器中计算出世界空间下的法线,然后再拿去进行需要的计算:

• 利用点积操作，得出世界空间下的法线（法线纹理）

half3 normalTex = UnpackNormalWithScale(tex2D(_NormalTex,i.uv),scale);
half3 worldNormal = half3(dot(i.tSpace0,normalTex),dot(i.tSpace1,normalTex),dot(i.tSpace2,normalTex));

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三、最终效果

最终代码：

//纹理的多级渐远 Mipmap
//纹理的环绕方式
//法线贴图
Shader "MyShader/P2_1_8"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        
        [KeywordEnum (Repeat,Clamp)]_WrapMode("WrapMode",int) = 0
        [IntRange]_Mipmap ("Mipmap",Range(0,10)) = 0
        
        //法线贴图
        [Normal]_NormalTex("NormalTex",2D) = "bump" {}
        //在属性面板定义立方体纹理
        _CubeMap("CubeMap",Cube) = "white" {}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma shader_feature _WRAPMODE_REPEAT _WRAPMODE_CLAMP
            #include "UnityCG.cginc"
            
            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                
                half3 normal : NORMAL;
                float4 tangent : TANGENT;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
                float3 localPos : TEXCOORD1;
                float3 worldPos : TEXCOORD2;
                half3 worldNormal : TEXCOORD3;

                float3 tSpace0:TEXCOORD4;
                float3 tSpace1:TEXCOORD5;
                float3 tSpace2:TEXCOORD6;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            half _Mipmap;
            samplerCUBE _CubeMap;
            sampler2D _NormalTex;
            v2f vert (appdata v)
            {
                v2f o;
                
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                o.localPos = v.vertex.xyz;
                o.worldPos = mul(unity_ObjectToWorld,v.vertex);
                o.worldNormal = UnityObjectToWorldNormal(v.normal);

                half3 worldTangent = UnityObjectToWorldDir(v.tangent);
                //v.tangent.w:DCC软件中顶点UV值中的V值翻转情况.
                //unity_WorldTransformParams.w:模型缩放是否有奇数负值. 
                half tangentSign = v.tangent.w * unity_WorldTransformParams.w;

                half3 worldBinormal = cross(o.worldNormal, worldTangent) * tangentSign;


                o.tSpace0 = float3(worldTangent.x,worldBinormal.x,o.worldNormal.x);
                o.tSpace1 = float3(worldTangent.y,worldBinormal.y,o.worldNormal.y);
                o.tSpace2 = float3(worldTangent.z,worldBinormal.z,o.worldNormal.z);
                
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                //WrapMode
                #if _WRAPMODE_REPEAT
                i.uv = frac(i.uv);
                #elif _WRAPMODE_CLAMP
                    //法一:
                    //i.uv = clamp(i.uv,0,1);
                    //法二:
                    i.uv = saturate(i.uv);
                #endif
                float4 uvMipmap = fixed4(i.uv,0,_Mipmap);
                fixed4 col = tex2Dlod(_MainTex, uvMipmap);

                //法线纹理
                fixed3 normalTex = UnpackNormal(tex2D(_NormalTex,i.uv));
                
                
                //max(0,dot(N,L))
                fixed3 N1 = normalize(normalTex);
                fixed3 L = _WorldSpaceLightPos0.xyz;

                //return fixed4(normalTex,1);
                //计算出世界空间下的法线
                half3 worldNormal = half3(dot(i.tSpace0,normalTex),dot(i.tSpace1,normalTex),dot(i.tSpace2,normalTex));
                return max(0,dot(worldNormal,L));

                //CubeMap
                fixed4 cubemap = texCUBE(_CubeMap,i.localPos);
                //V,N,R
                fixed3 V = normalize(i.worldPos - _WorldSpaceCameraPos);
                fixed3 N = normalize(i.worldNormal);
                fixed3 R = reflect(V,N);
                cubemap = texCUBE(_CubeMap,R);
                
                return cubemap;
                
                return col;
            }
            ENDCG
        }
    }
}