Unity Sprite 灰色图效果

Shader "Sprite/SpriteGray"
{
	Properties
	{
	[PerRendererData] _MainTex("Sprite Texture", 2D) = "white" {}
	_Color("Tint", Color) = (1, 1, 1, 1)
		[MaterialToggle] PixelSnap("Pixel snap", Float) = 0
}

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

		Cull Off
			Lighting Off
			ZWrite Off
			Fog{ Mode Off }
		Blend One OneMinusSrcAlpha

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

			fixed4 _Color;

			v2f vert(appdata_t IN)
			{
				v2f OUT;
				OUT.vertex = mul(UNITY_MATRIX_MVP, IN.vertex);
				OUT.texcoord = IN.texcoord;
				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;
				c.xyz *= c.a;//不加这个，alpha值低的时候，白色会消失看不见。
				float gray = dot(c.xyz, float3(0.299, 0.587, 0.114));
				//float gray = dot(c.xyz, float3(0.333, 0.333, 0.334));
				c.xyz = float3(gray, gray, gray);
				return c;
			}
			ENDCG
		}
	}
}