#define D 128
#define N 512

struct VertexOut
{
	float4 VertexPosition		:POSITION;
	float2 TexCoord				:TEXCOORD;
};


/*
  Vertex program for cloud rendering 
*/
VertexOut VertexProgram( float4 Position :POSITION,
						float2 Texcoord: TEXCOORD
						)									
{
	VertexOut Out;	
	
	Out.VertexPosition=Position;
	Out.TexCoord=Texcoord;
	
	return Out;	
}

/*
  Fragment program for cloud rendering 
*/
float3 FragmentProgram(	VertexOut	In,
						uniform samplerRECT IllumTexture,
						uniform samplerRECT TauTexture,
						uniform samplerRECT VisMap,						
						uniform samplerRECT DirectIllum,
						uniform samplerRECT Phase,
						uniform float3 Alb_Op,
						uniform float3 SkyColor
						):COLOR
{	
	float3 Color=float3(0,0,0);
	
	int particle=floor(In.TexCoord.x);
	int direction=floor(In.TexCoord.y);		
	
	int vp=floor(texRECT(VisMap,float2(particle,direction)).r);
	
	if(vp<N)
	{
			Color=texRECT(DirectIllum,float2(vp,direction));
			float ds=texRECT(VisMap,float2(particle,direction)).g;
			float tau=texRECT(TauTexture,float2(particle,1)).r;
			//tau=5.0;
			//ds=0.1;
			//if(ds<0.1)ds=0.1;
			float alpha=1-exp(-ds*tau);
			//float alpha=Alb_Op.y;
		
			float3 I=texRECT(IllumTexture,float2(vp,direction));
			//Color+=I.rgb*(1-Alb_Op.y);
			Color+=I.rgb*(1-alpha);
						
			for(int d=0;d<D;d++)
			{
				I=texRECT(IllumTexture,float2(vp,d));
				//Color+=I.rgb*Alb_Op.z*texRECT(Phase,float2(d,direction)).r;
				Color+=I.rgb*alpha*Alb_Op.z*texRECT(Phase,float2(d,direction)).r;
			}
			
					
	}
	else
	{
		//Color=float3(2.2,2.9,4.5);	
		Color=SkyColor;	
	}
	
	return  Color;	
}