概述

实现原理

Shader代码实现

Properties {
	_MainTex ("Base (RGB)", 2D) = "white" {}
	_SnowTex ("SnowTexture(RGB)",2D) = "white"{}
	_SnowCount ("SnowCount", Range (0.0, 1)) = 0.078
}

			struct appdata_t {
				float4 vertex : POSITION;
				float2 texcoord : TEXCOORD0;
				float3 normal : NORMAL;
			};

			struct v2f {
				float4 vertex : SV_POSITION;
				half2 texcoord : TEXCOORD0;
				half2 snowUV : TEXCOORD1  ;
				fixed4 snow : COLOR;//定义一个四元数用来传递将积雪位置到frag函数
				UNITY_FOG_COORDS(1)
			};

float3 worldNormal = mul((float3x3)_Object2World ,v.normal );//将法线转换到世界空间
float rim = 1-saturate(dot(float3(0,1,0),worldNormal ));//将世界空间的法线方向与Y轴做点积运算
o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
o.snowUV = TRANSFORM_TEX(v.texcoord , _SnowTex);
o.snow = pow(rim,_SnowCount*64);//控制积雪的量，这个值将传入到frag函数里面用来混合两张贴图

Shader "PengLu/Unlit/SnowVF" {
Properties {
	_MainTex ("Base (RGB)", 2D) = "white" {}
	_SnowTex ("SnowTexture(RGB)",2D) = "white"{}
	_SnowCount ("SnowCount", Range (0.0, 1)) = 0.078
}

SubShader {
	Tags { "RenderType"="Opaque" }
	LOD 100
	
	Pass {  
		CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma multi_compile_fog
			
			#include "UnityCG.cginc"

			struct appdata_t {
				float4 vertex : POSITION;
				float2 texcoord : TEXCOORD0;
				float3 normal : NORMAL;
			};

			struct v2f {
				float4 vertex : SV_POSITION;
				half2 texcoord : TEXCOORD0;
				half2 snowUV : TEXCOORD1  ;
				fixed4 snow : COLOR;
				UNITY_FOG_COORDS(1)
			};

			sampler2D _MainTex;
			sampler2D _SnowTex;
			float4 _MainTex_ST,_SnowTex_ST;
			float _SnowCount;
			v2f vert (appdata_t v)
			{
				v2f o;
				o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
				float3 worldNormal = mul((float3x3)_Object2World ,v.normal );
				float rim = 1-saturate(dot(float3(0,1,0),worldNormal ));
				o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
				o.snowUV = TRANSFORM_TEX(v.texcoord , _SnowTex);
				o.snow = pow(rim,_SnowCount*64);								
								UNITY_TRANSFER_FOG(o,o.vertex);
				return o;
			}
			
			fixed4 frag (v2f i) : SV_Target
			{
				fixed4 col = tex2D(_MainTex, i.texcoord);
				fixed4 snow = tex2D(_SnowTex,i.snowUV);
				col = lerp(snow,col,saturate(i.snow));
				UNITY_APPLY_FOG(i.fogCoord, col);
				UNITY_OPAQUE_ALPHA(col.a);
			
				return col;
			}
		ENDCG
	}
}

}

带法线贴图效果的实现

Shader "PengLu/Unlit/SnowBumpVF" {
	Properties {
	_MainTex ("Base (RGB)", 2D) = "white" {}
	_BumpMap ("BaseBump", 2D) = "bump" {}
	_SnowTex ("SnowTexture(RGB)",2D) = "white"{}
	_SnowCount ("SnowCount", Range (0.01, 1)) = 0.078
}

SubShader {
	Tags { "RenderType"="Opaque" }
	LOD 200
	
	Pass {  
		CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma multi_compile_fog
			
			#include "UnityCG.cginc"


			struct v2f {
				float4 vertex : SV_POSITION;
				half2 texcoord : TEXCOORD0;
				half2 snowUV : TEXCOORD1  ;
				// fixed4 snow : COLOR;
				float3 tangent:TEXCOORD2;
				float3 binormal : TEXCOORD3;
				float3 normal : TEXCOORD4;
				UNITY_FOG_COORDS(1)
			};

			sampler2D _MainTex,_BumpMap;
			sampler2D _SnowTex;
			float4 _MainTex_ST,_SnowTex_ST;
			float _SnowCount;
			v2f vert (appdata_full v)
			{
				v2f o;
				o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
				o.tangent = v.tangent.xyz;
				o.normal = v.normal;
				o.binormal=cross(v.normal,v.tangent.xyz)*v.tangent.w;
				
				o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
				o.snowUV = TRANSFORM_TEX(v.texcoord , _SnowTex);
								UNITY_TRANSFER_FOG(o,o.vertex);
				return o;
			}
			
			fixed4 frag (v2f i) : SV_Target
			{
				fixed4 col = tex2D(_MainTex, i.texcoord);
				fixed4 snow = tex2D(_SnowTex,i.snowUV);
				float3x3 rotation=float3x3 (i.tangent.xyz,i.binormal,i.normal);
				float3 N = UnpackNormal(tex2D(_BumpMap,i.texcoord));
				N=normalize(mul(N,rotation));
				N = mul((float3x3)_Object2World ,N );
				float rim = 1-saturate(dot(float3(0,1,0),N));
				float4 lerpsnow = pow(rim,_SnowCount*16);
				col = lerp(snow,col,saturate(lerpsnow));
				UNITY_APPLY_FOG(i.fogCoord, col);
				UNITY_OPAQUE_ALPHA(col.a);
			
				return col;
			}
		ENDCG
	}
}

}

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