Shader 使按钮图片致灰

Shader "UI/Default Grey"
{
Properties
{
[PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
_Color ("Tint", Color) = (1,1,1,1)
_Stencil ("Stencil Ref", Float) = 0
}

SubShader
{
Tags
{
"Queue"="Transparent"
"IgnoreProjector"="True"
"RenderType"="Transparent"
"PreviewType"="Plane"
"CanUseSpriteAtlas"="True"
}
// 源rgba*源a + 背景rgba*(1-源A值)
Blend SrcAlpha OneMinusSrcAlpha

Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#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;
};

sampler2D _MainTex;
fixed4 _Color;

v2f vert(appdata_t IN)
{
v2f OUT;
OUT.vertex = mul(UNITY_MATRIX_MVP, IN.vertex);
OUT.texcoord = IN.texcoord;
#ifdef UNITY_HALF_TEXEL_OFFSET
OUT.vertex.xy -= (_ScreenParams.zw-1.0);
#endif
OUT.color = IN.color * _Color;
return OUT;
}

fixed4 frag(v2f IN) : SV_Target
{
half4 color = tex2D(_MainTex, IN.texcoord) * IN.color;
float grey = dot(color.rgb, fixed3(0.22, 0.707, 0.071));
return half4(grey,grey,grey,color.a);
}
ENDCG
}
}
}

网上看到的，具体不不清楚，忘记链接了，借来用用。