Unity shader始终显示被遮挡物体

Shader "Custom/PathNode"
{
	Properties{
		 _Color("Color", Color) = (1,1,1,1)
		 _MainTex("Albedo (RGB)", 2D) = "white" {}
	}
	SubShader{
		Cull Off
		Pass
		{
			ZTest Greater
		}
		Pass
		{
			ZTest Less
		}
		Pass
		{
			ZTest Always
		}
		Tags { "RenderType" = "Opaque" }
		LOD 200

		CGPROGRAM
		// Physically based Standard lighting model, and enable shadows on all light types
		#pragma surface surf Standard fullforwardshadows
		// Use shader model 3.0 target, to get nicer looking lighting
		#pragma target 3.0
		sampler2D _MainTex;
		struct Input {
			float2 uv_MainTex;
		};
		fixed4 _Color;
		void surf(Input IN, inout SurfaceOutputStandard o) {
			// Albedo comes from a texture tinted by color
			fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
			o.Albedo = c.rgb;
			// Metallic and smoothness come from slider variables
			o.Alpha = c.a;
		}
		ENDCG
	}
		FallBack "Diffuse"
}