Unity3D Planar Shadows(平面阴影 CG Shader 04)

Shader "Unlit/PlanarShadow" {
	Properties{
		_MainTex ("My Texture", 2D) = "white" {}
	}
	SubShader {
	pass {      
		Tags { "LightMode" = "ForwardBase" }
		SetTexture [_MainTex] {}
		//Lighting On
	}
	pass {   
		Tags { "LightMode" = "ForwardBase" } 
		Blend DstColor SrcColor
		zTest off
		CGPROGRAM
		#pragma vertex vert 
		#pragma fragment frag
		#include "UnityCG.cginc"
		float4x4 _World2Ground;
		float4x4 _Ground2World;
		float4 vert(float4 vertex: POSITION) : SV_POSITION
		{
			float3 litDir;
			litDir=WorldSpaceLightDir(vertex); 
			litDir=mul(_World2Ground,float4(litDir,0)).xyz;
			litDir=normalize(litDir);
			float4 vt;
			vt= mul(_Object2World, vertex);
			vt=mul(_World2Ground,vt);
			vt.x=vt.x-(vt.y/litDir.y)*litDir.x;
			vt.z=vt.z-(vt.y/litDir.y)*litDir.z;
			vt.y=0;
			//vt=mul(vt,_World2Ground);//back to world
			vt=mul(_Ground2World,vt);
			vt=mul(_World2Object,vt);
			return mul(UNITY_MATRIX_MVP, vt);
		}
		
 		float4 frag(void) : COLOR 
		{
			return float4(0.2,0.2,0.2,1);
		}
 		ENDCG 
		}
   }
}