struct VS_OUT
{
	float4 hPosition	: POSITION;
	float4 color		: COLOR0;	
};

VS_OUT CauVS(float4 position : POSITION,	
		float4 texCoord : TEXCOORD0,
		float4 color 	: COLOR0,
		uniform float4x4 worldView,
		uniform float4x4 Proj,
		uniform float resolution,
		uniform sampler2D PhotonHitMap : register(s0))
{
  VS_OUT OUT;
     
  float4 cPosition;
  float pixel = 1.0 / resolution;   
  float2 uv = float2(position.x, 1.0 - position.y);
  float4 pos = tex2Dlod(PhotonHitMap, float4(uv,0,0)).rgba;

   if(pos.a == 0)//no photon hit
   {
		OUT.color = float4(0,0,0,0);		
		OUT.hPosition = float4(0, 0, 100000000, 1);
   }
   else
   {
   		float4 wPosition = float4(normalize(pos.xyz),1);    
		cPosition = mul(worldView, wPosition);
		OUT.hPosition = mul(Proj, cPosition);
		
		float intensity = 0.5;
		
		//read four neighbours
		float valids = 0;
		float sumdist = 0;
		float dist;
		float4 pos1 = tex2Dlod(PhotonHitMap, float4(uv + float2(pixel, pixel),0,0)).rgba;
		if(pos1.a != 0)
		{
			dist = length(pos1.xyz - pos.xyz);
			valids++;
			sumdist += dist;
		}
		float4 pos2 = tex2Dlod(PhotonHitMap, float4(uv + float2(-pixel, pixel),0,0)).rgba;
		if(pos2.a != 0)
		{
			dist = length(pos2.xyz - pos.xyz);
			valids++;
			sumdist += dist;
		}
		float4 pos3 = tex2Dlod(PhotonHitMap, float4(uv + float2(pixel, -pixel),0,0)).rgba;
		if(pos3.a != 0)
		{
			dist = length(pos3.xyz - pos.xyz);
			valids++;
			sumdist += dist;
		}
		float4 pos4 = tex2Dlod(PhotonHitMap, float4(uv + float2(-pixel, -pixel),0,0)).rgba;
		if(pos4.a != 0)
		{
			dist = length(pos4.xyz - pos.xyz);
			valids++;
			sumdist += dist;
		}
		
		float avrdist = sumdist / valids;
		float maxdist = 0.1;
		intensity = max(maxdist - avrdist, 0.0) / maxdist;
		
		OUT.color = float4(1,1,1,intensity);
	}  
   
   return OUT;
}


float4 CauPS(VS_OUT IN,
		uniform float3 color ):COLOR
{ 
  return IN.color * float4(color, 1);  
}