替换unity自身的mask遮罩

新建材质球，设置图，新建image，赋值材质球即可

Shader "ImageEffect/MaskIcon"
{
    Properties
    {
        [PerRendererData] _MainTex("Sprite Texture", 2D) = "white" {}
    _Mask("Base (RGB)", 2D) = "white" {}


    _Color("Tint", Color) = (1,1,1,1)
        _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
        _ColorMask("Color Mask", Float) = 15
        [Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip("Use Alpha Clip", Float) = 0
    }

        SubShader
    {
        Tags
    {
        "Queue" = "Transparent"
        "IgnoreProjector" = "True"
        "RenderType" = "Transparent"
        "PreviewType" = "Plane"
        "CanUseSpriteAtlas" = "True"
    }

        Stencil
    {
        Ref[_Stencil]
        Comp[_StencilComp]
        Pass[_StencilOp]
        ReadMask[_StencilReadMask]
        WriteMask[_StencilWriteMask]
    }

        Cull Off
        Lighting Off
        ZWrite Off
        ZTest[unity_GUIZTestMode]
        Blend SrcAlpha OneMinusSrcAlpha
        ColorMask[_ColorMask]

        Pass
    {
        CGPROGRAM
#pragma vertex vert
#pragma fragment frag

#include "UnityCG.cginc"
#include "UnityUI.cginc"

#pragma multi_compile __ UNITY_UI_ALPHACLIP

        struct a2v
    {
        fixed2 uv : TEXCOORD0;
        half4 vertex : POSITION;
        float4 color    : COLOR;
    };

    fixed4 _Color;

    struct v2f
    {
        fixed2 uv : TEXCOORD0;
        half4 vertex : SV_POSITION;
        float4 color    : COLOR;
    };

    sampler2D _MainTex;
    sampler2D _Mask;

    v2f vert(a2v i)
    {
        v2f o;
        o.vertex = mul(UNITY_MATRIX_MVP, i.vertex);
        o.uv = i.uv;

        o.color = i.color * _Color;
        return o;
    }

    fixed4 frag(v2f i) : COLOR
    {
        half4 color = tex2D(_MainTex, i.uv) * i.color;
        half4 mask = tex2D(_Mask, i.uv);
        color.a *= mask.a;
        return color;
    }
        ENDCG
    }
    }
}