使用shader实现UI按钮置灰的操作

shader代码

Shader "Custom/Gray" 
{
	Properties
	{
		[PerRendererData] _MainTex("Sprite Texture", 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
	}

	SubShader
	{
		Tags
		{
			"Queue" = "Transparent"
			"IgnoreProjector" = "True"
			"RenderType" = "Transparent"
			"PreviewType" = "Plane"
			"CanUseSpriteAltas" = "True"
		}
		Stencil
		{
			Ref[_Stencil]
			Comp[_StencilComp]
			Pass[_StencilOp]
			ReadMask[_StencilReadMask]
			WriteMask[_StencilWriteMask]
		}
		Cull Off 
		Lighting Off 
		ZWrite Off 
		ZTest[unity_GUIZTeseMode]
		Blend SrcAlpha OneMinusSrcAlpha
		ColorMask[_ColorMask]
		Pass 
		{
			CGPROGRAM

			#pragma vertex vert 
			#pragma fragment frag 
			#include "UnityCG.cginc"
			struct appdata_t 
			{
				float4 vertex :POSITION;
				float4 color :COLOR;
				float2 textcoord : TEXCOORD0;
			};
			struct v2f 
			{
				float4 vertex : SV_POSITION;
				fixed4 color : COLOR;
				half2 texcoord : TEXCOORD0;
			};
			fixed4 _Color;
			v2f vert(appdata_t IN)
			{
				v2f OUT;
				OUT.vertex = mul(UNITY_MATRIX_MVP, IN.vertex);
				OUT.texcoord = IN.textcoord;
			#ifdef UNITY_HALF_TEXEL_OFFSET
				OUT.vertex.xy += (_ScreenParams.zw - 1.0) * float2(-1, 1);
			#endif 
				OUT.color = IN.color * _Color;
				return OUT;
			}
			sampler2D _MainTex;
			fixed4 frag(v2f IN) : SV_Target 
			{
				half4 color = tex2D(_MainTex, IN.texcoord) * IN.color;
				clip(color.a - 0.01);

				half3 temp = dot(color.rgb,fixed3(.222, .707,.071));
				return half4(temp.r, temp.g, temp.b, color.a);
			}

			ENDCG
		}
	}
}

效果如图：

右边的是正常图，左边的是效果图