[游戏开发]Unity Shader 法线贴图

像素着色器在计算每个像素的光照时，会计算这个像素所在的面的法向量，而这个面的法向量也是由这个面周围的顶点法线插值得来的，把纹理采样的思想用在这里，直接用一张贴图来存储法线，在采样diffuse贴图时，再采样一张法线贴图，就可以修改法线了，通过改变法线来改变面上某个点的光照条件，就有凹凸的感觉了，这里用的是切线空间的法线纹理。

要得到法线的方向其实就是像素映射的逆函数：normal = pixel x 2 - 1
贴代码：

Shader "PLM/Table" {
	Properties {
		_Color ("Color Tint", Color) = (1, 1, 1, 1)
		_MainTex ("Main Tex", 2D) = "white" {}
		_Diffuse ("Diffuse", Color) = (1, 1, 1, 1)
		_Specular("Specular",Color) = (1,1,1,1)
        _Gloss("Gloss",Range(8.0,256)) = 20
		_BumpMap ("Normal Map", 2D) = "bump" {}
		_BumpScale ("Bump Scale", Float) = 1.0

	}
	SubShader {
		Pass {
			Tags { "LightMode"="ForwardBase" }

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

			fixed4 _Color;
			sampler2D _MainTex;
			float4 _MainTex_ST;
			fixed4 _Diffuse;
            fixed4 _Specular;
            float _Gloss;
			sampler2D _BumpMap;
			float4 _BumpMap_ST;
			float _BumpScale;

			struct a2v {
				float4 vertex : POSITION;
				float3 normal : NORMAL;
				float4 tangent : TANGENT;
				float4 texcoord : TEXCOORD0;
			};

			struct v2f {
				float4 pos : SV_POSITION;
				float4 uv : TEXCOORD0;
				//float3 worldPos : TEXCOORD1;
				//float3 worldNormal : TEXCOORD2;
				float3 lightDirNor : TEXCOORD3;
				float3 viewDirNor : TEXCOORD4;
			};

			v2f vert(a2v v) {
				v2f o;
				o.pos = UnityObjectToClipPos(v.vertex);
				o.uv.xy = v.texcoord.xy * _MainTex_ST.xy + _MainTex_ST.zw;
				o.uv.zw = v.texcoord.xy * _BumpMap_ST.xy + _BumpMap_ST.zw;
				TANGENT_SPACE_ROTATION;
				//o.worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
				//o.worldNormal = UnityObjectToWorldNormal(v.normal);
				o.lightDirNor = mul(rotation, ObjSpaceLightDir(v.vertex)).xyz;
				o.viewDirNor = mul(rotation, normalize(ObjSpaceViewDir(v.vertex))).xyz;

				return o;
			}

			fixed4 frag(v2f i) : SV_Target {
				fixed3 tangentLightDir = normalize(i.lightDirNor);
				fixed3 tangentViewDir = normalize(i.viewDirNor);
				fixed4 packedNormal = tex2D(_BumpMap, i.uv.zw);
				fixed3 tangentNormal;

				tangentNormal = UnpackNormal(packedNormal);
				tangentNormal.xy *= _BumpScale;
				tangentNormal.z = sqrt(1.0 - saturate(dot(tangentNormal.xy, tangentNormal.xy)));
				
				//float3 worldPos = i.worldPos;
				//fixed3 lightDir = normalize(UnityWorldSpaceLightDir(worldPos));
//diffuse
				fixed3 albedo = tex2D(_MainTex, i.uv).rgb * _Color.rgb;
				fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz * albedo;
				//fixed3 worldNormal=normalize(i.worldNormal); //世界空间下法线单位矢量
				//fixed3 worldLightDir=normalize(_WorldSpaceCameraPos.xyz); //世界空间下光源方向单位矢量
				
				fixed3 diffuse = _LightColor0.rgb * albedo * max(0, dot(tangentNormal, tangentLightDir));
				//fixed3 diffuse = _LightColor0.rgb * albedo * max(0, dot(i.worldNormal, lightDir));
				fixed3 halfDir = normalize(tangentLightDir + tangentViewDir);
				
				//fixed3 reflectDir=normalize(reflect(-worldLightDir,worldNormal)); //世界空间下反射光矢量
				//fixed3 viewDir=normalize(_WorldSpaceCameraPos.xyz-i.worldPos.xyz); //视野方向
				fixed3 specular = _LightColor0.rgb * _Specular.rgb * pow(max(0, dot(tangentNormal, halfDir)), _Gloss);
				//fixed3 specular = _LightColor0.rgb * _Specular.rgb * pow(saturate(dot(reflectDir,viewDir)),_Gloss);//高光

				return fixed4((ambient + diffuse + specular), 1.0);
			}
			ENDCG
		}
	}
	FallBack "Specular"
}

效果：