透明Shader的问题

[u013898924]

一个物体切割的显示的shader,设置 "Queue"="Transparent" 就会这样(如下图),
感觉是深度检测导致的,但是即使开了深度检测,换了各种参数,还是有问题.


如果将 tag改为"Queue"="AlphaTest"..里面遮挡住的物体又显示不了了...费解.


Shader代码如下..求大神指导......

Shader "lcc/Bumped Diffuse" {
Properties {
	_Color ("Main Color", Color) = (1,1,1,1)
	_MainTex ("Base (RGB) Gloss (A)", 2D) = "white" {}
	_Illum ("Illumin (A)", 2D) = "white" {}
	_BumpMap ("Normalmap", 2D) = "bump" {}
	_EmissionLM ("Emission (Lightmapper)", Float) = 0
	_ForwardLength("Forward",Float)=0
}
SubShader {
	  Tags{"Queue"="AlphaTest" "IgnoreProjector"="True" "RenderType"="Transparent"}
	  Cull off 
//       ZWrite off  
//        ZTest LEqual

CGPROGRAM
#pragma surface surf Lambert alpha vertex:vert 

sampler2D _MainTex;
sampler2D _BumpMap;
sampler2D _Illum;
fixed4 _Color;
float _ForwardLength;

struct Input {
	float2 uv_MainTex;
	float2 uv_Illum;
	float2 uv_BumpMap;
	float3 vertPos;  
};

void vert (inout appdata_full v, out Input o) {  
    UNITY_INITIALIZE_OUTPUT(Input,o);             
    o.vertPos = v.vertex;  
}  
void surf (Input IN, inout SurfaceOutput o) {
	fixed4 tex = tex2D(_MainTex, IN.uv_MainTex);
	fixed4 c = tex * _Color;
	o.Albedo = c.rgb;
	o.Emission = c.rgb * tex2D(_Illum, IN.uv_Illum).a;
	o.Normal = UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));

	if(IN.vertPos.z>_ForwardLength){
	o.Alpha = c.a;
	}else{
	o.Alpha =0;
	}
}
ENDCG
} 
FallBack "Self-Illumin/Diffuse"
}