【游戏-Shader】Shader实现体积光影。shader实现阴影基础上，实现体积光影的方法

LightTrail.shader

//思路：
//1.为了投影出体积阴影，我们多用一个pass来渲染网格。
//2.网格延伸的方向是灯光的方向。
//3.我们将顶点转换到模型空间，然后计算和灯光的角度进行顶点的偏移。
//4.因为根据顶点偏移，所以不能对断开的顶点进行平滑的过度。
//5.通过点乘插值我们来决定颜色的插值。
//6.该shader不仅可以用来做体积投影，也可以在灯光下做体积光。

//源代码：
Shader"QQ/LightTrail"  
{
	Properties  
	{
		//_FrontColor("FrontColor",Color)=(0.5,0.5,0.5,1)  
		_BackColor("BackColor",Color)=(0,0,0,1)  
		_LightColor("LightColor",Color)=(1,1,0,1)  
		_MainTex("Texture",2D)="white"{}
		_SmoothRange("SmoothRange",Range(0,20))=1  
		_TrailColor("TrailColor",Color)=(0,0,0,1)  
		_TrailPower("TrailPower",Range(0,10))=2  
		_TrailLength("TrailLength",Range(0,500))=100  
	}
	SubShader  
	{
		Tags
		{
			"RenderType"="Transparent"  
			"Queue"="Transparent"
		}
		LOD100  
		Pass  
		{
			Tags{"LightMode"="ForwardBase"}
			CGPROGRAM  
			#pragmavertexvert  
			#pragmafragmentfrag  
			#pragmamulti_compile_fog  
			#include"UnityCG.cginc"  
			structa2v  
			{
				float4vertex:POSITION;  
				float2uv:TEXCOORD0;  
				float3normal:NORMAL;  
			};  
			structv2f  
			{
				float2uv:TEXCOORD0;  
				float4vertex:SV_POSITION;  
				float4wPos:TEXCOORD1;  
				UNITY_FOG_COORDS(2)  
					float3normal:TEXCOORD3;  
				float2uv_mask:TEXCOORD4;  
			};  
			uniformfloat4_LightColor0;  
			//fixed4_FrontColor;  
			fixed4_BackColor;  
			fixed4_LightColor;  
			sampler2D_MainTex;  
			float4_MainTex_ST;  
			float_SmoothRange;  
			v2fvert(a2vv)  
			{
				v2fo;  
				o.vertex=mul(UNITY_MATRIX_MVP,v.vertex);  
				o.wPos=mul(unity_ObjectToWorld,v.vertex);  
				_MainTex_ST.zw*=_Time.x;  
				o.uv=TRANSFORM_TEX(v.uv,_MainTex);  
				o.normal=UnityObjectToWorldNormal(v.normal);  
				UNITY_TRANSFER_FOG(o,o.vertex);  
				returno;  
			}
			fixed4frag(v2fi):SV_Target  
			{
				floatnor=dot(i.normal,normalize(UnityWorldSpaceLightDir(i.wPos)));  
				fixed4col=tex2D(_MainTex,i.uv);  
				float_front=saturate(nor*_SmoothRange);  
				col*=lerp(_BackColor,_LightColor0,_front);  
				col+=_LightColor*min(1-_front,col.a);  
				UNITY_APPLY_FOG(i.fogCoord,col);  
				returncol;  
			}
			ENDCG  
		}
		Pass  
		{
			Tags{"LightMode"="ForwardBase"}
			ZWriteOff  
			CullOff  
			BlendSrcAlphaOneMinusSrcAlpha  
			CGPROGRAM  
			#pragmavertexvert  
			#pragmafragmentfrag  
			#pragmamulti_compile_fog  
			#include"UnityCG.cginc"  
			structa2v  
			{
				float4vertex:POSITION;  
				float3normal:NORMAL;  
			};  
			structv2f  
			{
				float4vertex:SV_POSITION;  
				float3wPos:TEXCOORD1;  
				float3normal:TEXCOORD2;  
				UNITY_FOG_COORDS(3)  
			};  
			fixed4_TrailColor;  
			float_TrailPower;  
			float_TrailLength;  
			v2fvert(a2vv)  
			{
				v2fo;  
				o.wPos=mul(unity_ObjectToWorld,v.vertex);  
				o.normal=UnityObjectToWorldNormal(v.normal);  
				v.vertex.xyz+=v.normal*0.01;  
				o.vertex=mul(UNITY_MATRIX_M,v.vertex);  
				float3lightDir=normalize(UnityWorldSpaceLightDir(o.wPos));  
				floatNdotL=min(0,dot(o.normal,lightDir.xyz));  
				o.vertex.xyz+=lightDir*NdotL*_TrailLength;  
				o.vertex=mul(UNITY_MATRIX_VP,o.vertex);  
				UNITY_TRANSFER_FOG(o,o.vertex);  
				returno;  
			}
			fixed4frag(v2fi):SV_Target  
			{
				floatnor=dot(i.normal,normalize(UnityWorldSpaceLightDir(i.wPos)));  
				fixed4col=_TrailColor*(pow(1.5*_TrailColor.a-abs(nor),_TrailPower));  
				UNITY_APPLY_FOG(i.fogCoord,col);  
				returncol;  
			}
			ENDCG  
		}
		Pass  
		{
			BlendOneOne  
			Tags{"LightMode"="ForwardAdd"}
			CGPROGRAM  
			#pragmavertexvert  
			#pragmafragmentfrag  
			#pragmamulti_compile_fog  
			#include"UnityCG.cginc"  
			structa2v  
			{
				float4vertex:POSITION;  
				float2uv:TEXCOORD0;  
				float3normal:NORMAL;  
			};  
			structv2f  
			{
				float2uv:TEXCOORD0;  
				float4vertex:SV_POSITION;  
				float4wPos:TEXCOORD1;  
				UNITY_FOG_COORDS(2)  
					float3normal:TEXCOORD3;  
				float2uv_mask:TEXCOORD4;  
			};  
			uniformfloat4_LightColor0;  
			//fixed4_FrontColor;  
			fixed4_BackColor;  
			fixed4_LightColor;  
			sampler2D_MainTex;  
			float4_MainTex_ST;  
			float_SmoothRange;  
			v2fvert(a2vv)  
			{
				v2fo;  
				o.vertex=mul(UNITY_MATRIX_MVP,v.vertex);  
				o.wPos=mul(unity_ObjectToWorld,v.vertex);  
				_MainTex_ST.zw*=_Time.x;  
				o.uv=TRANSFORM_TEX(v.uv,_MainTex);  
				o.normal=UnityObjectToWorldNormal(v.normal);  
				UNITY_TRANSFER_FOG(o,o.vertex);  
				returno;  
			}
			fixed4frag(v2fi):SV_Target  
			{
				floatnor=dot(i.normal,normalize(UnityWorldSpaceLightDir(i.wPos)));  
				fixed4col=tex2D(_MainTex,i.uv);  
				float_front=saturate(nor*_SmoothRange);  
				col*=lerp(_BackColor,_LightColor0,_front);  
				col+=_LightColor*min(1-_front,col.a);  
				UNITY_APPLY_FOG(i.fogCoord,col);  
				returncol;  
			}
			ENDCG  
		}
		Pass  
		{
			Tags{"LightMode"="ForwardAdd"}
			ZWriteOff  
			CullOff  
			BlendSrcAlphaOneMinusSrcAlpha  
			CGPROGRAM  
			#pragmavertexvert  
			#pragmafragmentfrag  
			#pragmamulti_compile_fog  
			#include"UnityCG.cginc"  
			structa2v  
			{
				float4vertex:POSITION;  
				float3normal:NORMAL;  
			};  
			structv2f  
			{
				float4vertex:SV_POSITION;  
				float3wPos:TEXCOORD1;  
				float3normal:TEXCOORD2;  
				UNITY_FOG_COORDS(3)  
			};  
			fixed4_TrailColor;  
			float_TrailPower;  
			float_TrailLength;  
			v2fvert(a2vv)  
			{
				v2fo;  
				o.wPos=mul(unity_ObjectToWorld,v.vertex);  
				o.normal=UnityObjectToWorldNormal(v.normal);  
				v.vertex.xyz+=v.normal*0.01;  
				o.vertex=mul(UNITY_MATRIX_M,v.vertex);  
				float3lightDir=normalize(UnityWorldSpaceLightDir(o.wPos));  
				floatNdotL=min(0,dot(o.normal,lightDir.xyz));  
				o.vertex.xyz+=lightDir*NdotL*_TrailLength;  
				o.vertex=mul(UNITY_MATRIX_VP,o.vertex);  
				UNITY_TRANSFER_FOG(o,o.vertex);  
				returno;  
			}
			fixed4frag(v2fi):SV_Target  
			{
				floatnor=dot(i.normal,normalize(UnityWorldSpaceLightDir(i.wPos)));  
				fixed4col=_TrailColor*(pow(1.5*_TrailColor.a-abs(nor),_TrailPower));  
				UNITY_APPLY_FOG(i.fogCoord,col);  
				returncol;  
			}
			ENDCG  
		}
	}
}

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