#ifndef __CLUSTEREDUTILS_H__
#define __CLUSTEREDUTILS_H__

#ifndef FLT_EPSILON
	#define FLT_EPSILON     1.192092896e-07f
#endif

float GetScaleFromBase(float base)
{
	const float C = (float) (1<<g_iLog2NumClusters);
	const float geomSeries = (1.0 - pow(base, C))/(1-base);		// geometric series: sum_k=0^{C-1} base^k
	return geomSeries/(g_fFarPlane-g_fNearPlane);
}

int SnapToClusterIdxFlex(float z_in, float suggestedBase, bool logBasePerTile)
{
#ifdef LEFT_HAND_COORDINATES
	float z = z_in;
#else
	float z = -z_in;
#endif

	float userscale = g_fClustScale;
	if(logBasePerTile)
		userscale = GetScaleFromBase(suggestedBase);

	// using the inverse of the geometric series
	const float dist = max(0, z-g_fNearPlane);
	return (int) clamp( log2(dist*userscale*(suggestedBase-1.0f) + 1) / log2(suggestedBase), 0.0, (float) ((1<<g_iLog2NumClusters)-1) );
}

int SnapToClusterIdx(float z_in, float suggestedBase)
{
#ifdef ENABLE_DEPTH_TEXTURE_BACKPLANE
	bool logBasePerTile = true;		// resolved compile time
#else
	bool logBasePerTile = false;
#endif

	return SnapToClusterIdxFlex(z_in, suggestedBase, logBasePerTile);
}

float ClusterIdxToZFlex(int k, float suggestedBase, bool logBasePerTile)
{
	float res;

	float userscale = g_fClustScale;
	if(logBasePerTile)
		userscale = GetScaleFromBase(suggestedBase);

	float dist = (pow(suggestedBase,(float) k)-1.0)/(userscale*(suggestedBase-1.0f));
	res = dist+g_fNearPlane;

#ifdef LEFT_HAND_COORDINATES
	return res;
#else
	return -res;
#endif
}

float ClusterIdxToZ(int k, float suggestedBase)
{
#ifdef ENABLE_DEPTH_TEXTURE_BACKPLANE
	bool logBasePerTile = true;		// resolved compile time
#else
	bool logBasePerTile = false;
#endif

	return ClusterIdxToZFlex(k, suggestedBase, logBasePerTile);
}

// generate a log-base value such that half of the clusters are consumed from near plane to max. opaque depth of tile.
float SuggestLogBase50(float tileFarPlane)
{
	const float C = (float) (1<<g_iLog2NumClusters);
	float normDist = clamp( (tileFarPlane-g_fNearPlane) / (g_fFarPlane-g_fNearPlane), FLT_EPSILON, 1.0);
	float suggested_base = pow( (1.0 + sqrt(max(0.0,1.0-4.0*normDist*(1.0-normDist))))/(2.0*normDist), 2.0/C);		// 
	return max(g_fClustBase, suggested_base);
}

// generate a log-base value such that (approximately) a quarter of the clusters are consumed from near plane to max. opaque depth of tile.
float SuggestLogBase25(float tileFarPlane)
{
	const float C = (float) (1<<g_iLog2NumClusters);
	float normDist = clamp( (tileFarPlane-g_fNearPlane) / (g_fFarPlane-g_fNearPlane), FLT_EPSILON, 1.0);
	float suggested_base = pow( (1/2.3)*max(0.0, (0.8/normDist)-1), 4.0/(C*2));		// approximate inverse of d*x^4 + (-x) + (1-d) = 0		- d is normalized distance
	return max(g_fClustBase,suggested_base);
}


#endif