unity中如何实现UGUI遮罩流光特效

Shader "UI/Unlit/Flowlight"{  Properties  {    [PerRendererData] _MainTex("Sprite Texture", 2D) = "white" {}    _Color("Tint", Color) = (1, 1, 1, 1)    [MaterialToggle] _OffSet("OffSet", float) = 0    [MaterialToggle] PixelSnap("Pixel snap", float) = 0    /* Flowlight */    _FlowlightMaskTex("Mask Texture", 2D) = "white" {}    _FlowlightTex("Add Move Texture", 2D) = "white" {}    _FlowlightColor("Flowlight Color", Color) = (0, 0, 0, 1)    _Power("Power", float) = 1    _SpeedX("SpeedX", float) = 1    _SpeedY("SpeedY", float) = 0    /* --------- */    /* UI */    _StencilComp("Stencil Comparison", Float) = 8    _Stencil("Stencil ID", Float) = 0    _StencilOp("Stencil Operation", Float) = 0    _StencilWriteMask("Stencil Write Mask", Float) = 255    _StencilReadMask("Stencil Read Mask", Float) = 255    /* -- */  }  SubShader  {    Tags    {      "Queue" = "Transparent"      "IgnoreProjector" = "True"      "RenderType" = "Transparent"      "PreviewType" = "Plane"      "CanUseSpriteAtlas" = "True"    }    Cull Off    Lighting Off    ZWrite Off    Blend One OneMinusSrcAlpha    /* UI */    Stencil    {      Ref[_Stencil]      Comp[_StencilComp]      Pass[_StencilOp]      ReadMask[_StencilReadMask]      WriteMask[_StencilWriteMask]    }    /* -- */  Pass  {    CGPROGRAM#pragma vertex vert#pragma fragment frag#pragma multi_compile _ PIXELSNAP_ON#include "UnityCG.cginc"  struct appdata_t  {    float4 vertex : POSITION;    float4 color : COLOR;    float2 texcoord : TEXCOORD0;  };  struct v2f  {    float4 vertex : SV_POSITION;    fixed4 color : COLOR;    half2 texcoord : TEXCOORD0;    /* Flowlight */    half2 texflowlight : TEXCOORD1;    /* --------- */  };  fixed4 _Color;  /* Flowlight */  fixed4 _FlowlightColor;  float _Power;  sampler2D _FlowlightTex;  fixed4 _FlowlightTex_ST;  sampler2D _FlowlightMaskTex;  fixed4 _FlowlightMaskTex_ST;  fixed _SpeedX;  fixed _SpeedY;  fixed x = 0;  float _OffSet;  /* --------- */  v2f vert(appdata_t IN)  {    v2f OUT;    OUT.vertex = mul(UNITY_MATRIX_MVP, IN.vertex);    OUT.texcoord = IN.texcoord;    /* Flowlight */    OUT.texflowlight = TRANSFORM_TEX(IN.texcoord, _FlowlightTex);    OUT.texflowlight.x += _Time * _SpeedX;    OUT.texflowlight.y += _Time * _SpeedY;    OUT.color = IN.color * _Color;#ifdef PIXELSNAP_ON    OUT.vertex = UnityPixelSnap(OUT.vertex);#endif    return OUT;  }  sampler2D _MainTex;  fixed4 frag(v2f IN) : SV_Target  {    fixed4 c = tex2D(_MainTex, IN.texcoord)*IN.color;    fixed4 cmask = tex2D(_FlowlightMaskTex, IN.texcoord);  if (cmask.a != 0)  {    /* Flowlight */    fixed4 cadd = tex2D(_FlowlightTex, IN.texflowlight) * _Power;    cadd.rgb *= c.rgb;    c.rgb += cadd.rgb;  }  c.rgb *= c.a;  /* --------- */  return c;  }    ENDCG  }  }}