人物走过的草丛，自动出现被踩踏的效果

其实基本原理就是将主角的位置传进shader的_MainPlayerPos，然后根据顶点和人物的位置进行相减求出方向向量，然后进行一个位置的偏移。

但是这种效果的开销是蛮大的，如果是对一整片草(一个obj)进行传值，并且只是进入一定范围才会进行传值，效果还是可以接受的。不过再怎么也没有美术的动画看起来真实，但是美术的动画不会针对一片草进行动画啦。可以配合在一起用，效果是不错的。

Shader"AnimalClamp/GrassMoveByVertex"   //人物走过的草丛，自动出现被踩踏的效果

{

       Properties

       {

              _MainTex ("Texture", 2D) = "white" {}

              _MainTex_Alpha("(A)", 2D) = "white" {}

              _Brightness("Brightness", range(0, 5)) = 1

              _AlphaCutoff("Alpha Cutoff",range(0, 1)) = 1

              _RefluenceDistance("Refluence Distance",float) = 1           //受影响的上限范围，大于该值等于0，就不再受影响了

              _RefluenceArgs("Refluence Args",range(0,10)) = 0              //影响的参数，即最终的一个范围值的上限

              _BlugeShape("Bluge Shape",float) = 5

              _BlugeScale("Bluge Scale",float) = 5

              _BlugeSquare("Bluge Square",float) = 5                              //影响范围的参数

              [HideInInspector]_MainPlayerPos("Main Player Pos",color) = (1,1,1,0)

       }

       SubShader

       {

              Tags{"Queue"="Transparent""RenderType"="Opaque"}

              Pass

              {

                     ZWrite On

                     Blend SrcAlpha OneMinusSrcAlpha

                     CGPROGRAM

                     #pragmavertex vert

                     #pragmafragment frag

                     #pragmatarget 2.0

                     #include"UnityCG.cginc"

                     structappdata

                     {

                           float4vertex : POSITION;

                           float3normal : NORMAL;

                           float4tangent : TANGENT;

                           float2uv : TEXCOORD0;

                     };

                     structv2f

                     {

                           float4pos : SV_POSITION;

                           float2uv : TEXCOORD0;

                           float3square : TEXCOORD1; //娱乐，写着玩的

                     };

                     float_Brightness;

                     sampler2D_MainTex;

                     sampler2D_MainTex_Alpha;

                     float_AlphaCutoff;

                     float4_MainPlayerPos;

                     float_RefluenceDistance;

                     float_RefluenceArgs;

                     float_BlugeShape;

                     float_BlugeScale;

                     float_BlugeSquare;

                     half4tex2D_ETC1(sampler2Dtex,sampler2Dalpha,half2uv)//3

                     {

                           half4final = tex2D(tex, uv);

                           final.a = min(1, tex2D(alpha, uv).r);

                           returnfinal;

                     }

                     v2f vert (appdata v)

                     {

                           v2f o;                                   

                           o.uv = v.uv;

                           float3objVertex = mul(unity_ObjectToWorld, v.vertex).xyz;//先将顶点转换到世界空间

                           float3vertexVec = objVertex.xyz - _MainPlayerPos.xyz;//pos到顶点的方向向量

                           floatdistance = sqrt(vertexVec.x * vertexVec.x + vertexVec.z * vertexVec.z);//距离因子，只控制了x & z，如果需要可以把 y 写进去                      + vertexVec.y * vertexVec.y

                           float3moveArgs = 1 / distance * _BlugeSquare * vertexVec;    //顶点偏移的参数，没有错的

                           o.square = moveArgs;

                           float3moveOffset = moveArgs;// *objVertex.xyz * normalize(vertexVec);//(abs(distance) > _RefluenceDistance ? 0 :

                           float3offset = pow((abs((frac((o.uv + _Time.g *float2(0.25, 0)).r) - 0.5)) * 2), _BlugeShape) * v.normal * _BlugeScale;//草循坏摆动的经验公式

                           offset += clamp(moveArgs, -1, 1) ;//加上被压的offset,把这个值规定到-1到1，以免显示夸张

                           //这里的offset偏移量是依据复制出来的世界空间的顶点信息做得objVertex，包括空间坐标系转换都是用vertexVec ，而不可以直接用v.vertex，因为如果用v.vertex迭代的话，会出现一定距离的误差,这是一个深坑，不知道为什么的深坑

                           offset = mul(unity_WorldToObject, offset);

                           o.pos = UnityObjectToClipPos(v.vertex + offset);//+ vertexVec * distance 好玩的效果

                           returno;

                     }

                     

                     fixed4 frag (v2f i) : SV_Target

                     {

                           fixed4 col = tex2D_ETC1(_MainTex, _MainTex_Alpha, i.uv) ;

                           col.rgb *= _Brightness;

                           clip(col.a - _AlphaCutoff);

                           returncol *float4(i.square, 1);

                     }

                     ENDCG

              }

       }

       //FallBack "Diffuse" //半透明不要打开，因为FallBack中会绘制阴影

}