// Copyright (C) 2009-2016, Panagiotis Christopoulos Charitos and contributors.
// All rights reserved.
// Code licensed under the BSD License.
// http://www.anki3d.org/LICENSE

// Contains functions for the clusterer

#ifndef ANKI_SHADERS_CLUSTERER_GLSL
#define ANKI_SHADERS_CLUSTERER_GLSL

#include "shaders/Common.glsl"

// Compute the cluster index using the tile index.
uint computeClusterIndexUsingTileIdx(
	float near, float clustererMagic, float zVSpace, uint tileIdx, uint tileCountX, uint tileCountY)
{
	float fk = sqrt((zVSpace + near) * clustererMagic);
	uint k = uint(fk);

	return tileIdx + k * (tileCountX * tileCountY);
}

// Compute the cluster index using the a custom gl_FragCoord.xy.
uint computeClusterIndexUsingCustomFragCoord(
	float near, float clustererMagic, float zVSpace, uint tileCountX, uint tileCountY, vec2 fragCoord)
{
	// Compute tile idx
	uvec2 f = uvec2(fragCoord) >> 6;
	uint tileIdx = f.y * tileCountX + f.x;

	return computeClusterIndexUsingTileIdx(near, clustererMagic, zVSpace, tileIdx, tileCountX, tileCountY);
}

// Compute the cluster index using the gl_FragCoord.xy.
uint computeClusterIndexUsingFragCoord(
	float near, float clustererMagic, float zVSpace, uint tileCountX, uint tileCountY)
{
	return computeClusterIndexUsingCustomFragCoord(
		near, clustererMagic, zVSpace, tileCountX, tileCountY, gl_FragCoord.xy);
}

// Compute the Z of the near plane given a cluster idx
float computeClusterNear(uint k, float near, float clustererMagic)
{
	return 1.0 / clustererMagic * pow(float(k), 2.0) - near;
}

float computeClusterFar(uint k, float near, float clustererMagic)
{
	return 1.0 / clustererMagic * pow(float(k + 1u), 2.0) - near;
}

uint computeClusterKFromZViewSpace(float zViewSpace, float near, float far, float clustererMagic)
{
	float z = clamp(zViewSpace, -far, -near);
	z = -z;
	float kf = sqrt((z - near) * -clustererMagic);
	return uint(kf);
}

#endif