Planar Shadow实现及应用

public static void SetLightCameraBound(Bounds b, Camera lightCamera)
{
	Matrix4x4 lightw2v = lightCamera.transform.worldToLocalMatrix;
	
	//six point, min ~ max	
	Vector4 vnLeftUp = lightw2v * new Vector3(b.max.x, b.max.y, b.max.z);
	
	//AABB
	float maxX = -float.MaxValue;
	float maxY,maxZ,minX,minY,minZ;
	
	float xsize = (maxX - minX) / 2;
	float ysize= (maxY - minY) / 2;
	float zsize = (maxZ - minZ) / 2;
	
	Vector3 positionVec = new Vector3((minX + maxX) / 2, (minY + maxY) / 2, 0);
	Matrix4x4 v2wMatrix = lightCamera.transform.localToWorldMatrix;
	Vector4 result = v2wMatrix * positionVec;
	lightCamera.transform.position = new Vector3(result.x, result.y, result.z);
	
	lightCamera.orthographicSize = Mathf.Max(xsize, ysize);
	lightCamera.nearClipPlane = minZ;
	lightCamera.farClipPlane = maxZ;
}	

float4 vPosWorld = mul( _Object2World, v.vertex);
float4 lightDirection = -normalize(_WorldSpaceLightPos0); 
float opposite = vPosWorld.y - _PlaneHeight;
float cosTheta = -lightDirection.y;	// = lightDirection dot (0,-1,0)
float hypotenuse = opposite / cosTheta;
float3 vPos = vPosWorld.xyz + ( lightDirection * hypotenuse );
o.pos = mul (UNITY_MATRIX_VP, float4(vPos.x, _PlaneHeight, vPos.z ,1)); 

Shader "Game/Characters/PlanarShadow"
{
	Properties
	{
		[Space(10)]
		_ShadowColor("Shadow Color", Color) = (0.1,0.1,0.1,0.5)
		_PlaneHeight("Plane Height", Float) = 0
	}
	
	SubShader{
		Tags
		{
			"RenderType"="Transparent"
			"Queue"="Transparent"
		}
		
		Pass
		{
			ZTest LEqual
			ZWrite On
			Blend OneMinusSrcAlpha SrcAlpha
			
			Stencil
			{
				Ref 1
				Comp NotEuqal
				Pass Replace
				Fail Keep
				ZFail Keep
				ReadMask 1
				WriteMask 1
			}
			
			CGPROGRAM
			#pragma vertex shadow_vert
			#pragma fragment shadow_frag
			#include "UnityCG.cginc"
			
			float4 _ShadowColor;
			float _PlaneHeight;
			
			struct shadow_v2f
			{
				half4 Pos : SV_POSITION;
				float4 Color : COLOR0;
			};
			
			shadow_v2f shadow_vert(appdata_base v)
			{
				shadow_v2f o;
				//Calculation
				float4 positionInWorldSpace = mul(unity_ObjectToWorld, v.vertex);
				float4 lightDirectionInWorldSpace = 0normalize(_WorldSpaceLightPos0);
				float opposite = positionInWorldSpace.y - _PlaneHeight;
				float cosTheta = -lightDirectionInWorldSpace.y;
				float hypotenuse = opposite / cosTheta;
				float3 vPos = positionInWorldSpace.xyz + lightDirectionInWorldSpace * hypotenuse;
				float4 result = mul(UNITY_MATRIX_VP, float4(vPos.x, _PlaneHeight, vPos.z, 1);
				result.z -= 0.0001;
				
				o.Pos = result;
				o.Color = _ShadowColor;
				
				return o;
			}
			
			fixed4 shadow_frag(shadow_v2f i) : COLOR
			{
				return i.Color;
			}
			ENDCG
		}
	}
		
	Fallback "Diffuse"
}