Shader "Transparent/Mask"  
{  
   Properties  
   {  
      _MainTex ("Base (RGB)", 2D) = "white" {}  
      _Mask ("Culling Mask", 2D) = "white" {}  
      _Cutoff ("Alpha cutoff", Range (0,1)) = 0.1  
   }  
   SubShader  
   {  
      Tags {"Queue"="Transparent"}  
      Lighting Off  
      ZWrite Off  
      Blend Off  
      AlphaTest GEqual [_Cutoff]  
      Pass  
      {           
         SetTexture [_Mask] {combine texture}  
         SetTexture [_MainTex] {combine texture, previous}  
      }  
   }  
}