#include "stdafx.h"
#include "opengl/glew.h"
#include "skydome.h"
#include "color.h"

// sky gradient based on "A practical analytic model for daylight" 
// by A. J. Preetham Peter Shirley Brian Smits (University of Utah)

float CSkyDome::m_distributionluminance[ 5 ][ 2 ] = {	// Perez distributions
		{  0.17872f , -1.46303f },		// a = darkening or brightening of the horizon
		{ -0.35540f ,  0.42749f },		// b = luminance gradient near the horizon,
		{ -0.02266f ,  5.32505f },		// c = relative intensity of the circumsolar region
		{  0.12064f , -2.57705f },		// d = width of the circumsolar region
		{ -0.06696f ,  0.37027f }		// e = relative backscattered light
	};
float CSkyDome::m_distributionxcomp[ 5 ][ 2 ] = {
		{ -0.01925f , -0.25922f },
		{ -0.06651f ,  0.00081f },
		{ -0.00041f ,  0.21247f },
		{ -0.06409f , -0.89887f },
		{ -0.00325f ,  0.04517f }
	};
float CSkyDome::m_distributionycomp[ 5 ][ 2 ] = {
		{ -0.01669f , -0.26078f },
		{ -0.09495f ,  0.00921f },
		{ -0.00792f ,  0.21023f },
		{ -0.04405f , -1.65369f },
		{ -0.01092f ,  0.05291f }	
	};

float CSkyDome::m_zenithxmatrix[ 3 ][ 4 ] = {
		{  0.00165f, -0.00375f,  0.00209f,  0.00000f },
		{ -0.02903f,  0.06377f, -0.03202f,  0.00394f },
		{  0.11693f, -0.21196f,  0.06052f,  0.25886f }
	};
float CSkyDome::m_zenithymatrix[ 3 ][ 4 ] = {
		{  0.00275f, -0.00610f,  0.00317f,  0.00000f },
		{ -0.04214f,  0.08970f, -0.04153f,  0.00516f },
		{  0.15346f, -0.26756f,  0.06670f,  0.26688f }
	};

//******************************************************************************//

float clamp( float const Value, float const Min, float const Max ) {

    float value = Value;
    if( value < Min ) { value = Min; }
    if( value > Max ) { value = Max; }
    return value;
}

float interpolate( float const First, float const Second, float const Factor ) {

    return ( First * ( 1.0f - Factor ) ) + ( Second * Factor );
}

//******************************************************************************//

CSkyDome::CSkyDome (int const Tesselation) :
               m_tesselation( Tesselation ) {

//	SetSunPosition( Math3D::vector3(75.0f, 0.0f, 0.0f) );
	SetTurbidity( 3.5f );
	SetExposure( true, 16.0f );
	SetOvercastFactor( 0.08f );
	SetGammaCorrection( 2.2f );
    Generate();
}

CSkyDome::~CSkyDome() {
}

//******************************************************************************//

void CSkyDome::Generate() {
	// radius of dome
    float const radius = 1.0f; // 100.0f;

	// create geometry chunk
    int const latitudes = m_tesselation / 2;
    int const longitudes = m_tesselation;

    for( int i = 0; i < latitudes; ++i ) {

        float lat0 = M_PI * ( -0.5f + (float)( i ) / latitudes );
        float z0 = std::sin( lat0 );
        float zr0 = std::cos( lat0 );

        float lat1 = M_PI * ( -0.5f + (float)( i + 1 ) / latitudes );
        float z1 = std::sin( lat1 );
        float zr1 = std::cos( lat1 );

        // quad strip
        for( int j = 0; j <= longitudes / 2; ++j ) {

            float longitude = 2.0 * M_PI * (float)( j ) / longitudes;
            float x = std::cos( longitude );
            float y = std::sin( longitude );

            m_vertices.emplace_back( float3( x * zr0, y * zr0 - 0.1f, z0 ) * radius );
//            m_normals.emplace_back( float3( -x * zr0, -y * zr0, -z0 ) );
            m_colours.emplace_back( float3( 0.75f, 0.75f, 0.75f ) );

            m_vertices.emplace_back( float3( x * zr1, y * zr1 - 0.1f, z1 ) * radius );
//            m_normals.emplace_back( float3( -x * zr1, -y * zr1, -z1 ) );
            m_colours.emplace_back( float3( 0.75f, 0.75f, 0.75f ) );
        }
    }
}

//******************************************************************************//

void CSkyDome::Update( Math3D::vector3 const &Sun ) {

    if( true == SetSunPosition( Sun ) ) {
        // build colors if there's a change in sun position
        RebuildColors();
    }
}

// render skydome to screen
void CSkyDome::Render() {

    int const latitudes = m_tesselation / 2;
    int const longitudes = m_tesselation;
    int idx = 0;

    for( int i = 0; i < latitudes; ++i ) {

        ::glBegin( GL_QUAD_STRIP );
        for( int j = 0; j <= longitudes / 2; ++j ) {

            ::glColor3f( m_colours[ idx ].x, m_colours[ idx ].y, m_colours[ idx ].z );
//            ::glNormal3f( m_normals[ idx ].x, m_normals[ idx ].y, m_normals[ idx ].z );
            ::glVertex3f( m_vertices[ idx ].x, m_vertices[ idx ].y, m_vertices[ idx ].z );
            ++idx;
            ::glColor3f( m_colours[ idx ].x, m_colours[ idx ].y, m_colours[ idx ].z );
//            ::glNormal3f( m_normals[ idx ].x, m_normals[ idx ].y, m_normals[ idx ].z );
            ::glVertex3f( m_vertices[ idx ].x, m_vertices[ idx ].y, m_vertices[ idx ].z );
            ++idx;
        }
        glEnd();
    }
}

//******************************************************************************//

bool CSkyDome::SetSunPosition( Math3D::vector3 const &Direction ) {

    auto sundirection = SafeNormalize( float3( Direction.x, Direction.y, Direction.z) );
    if( sundirection == m_sundirection ) {

        return false;
    }

    m_sundirection = sundirection;
	m_thetasun = std::acosf( m_sundirection.y );
	m_phisun = std::atan2( m_sundirection.z , m_sundirection.x );

    return true;
}


void CSkyDome::SetTurbidity( float const Turbidity ) {

	m_turbidity = clamp( Turbidity, 1.0f, 512.0f );
}

void CSkyDome::SetExposure( bool const Linearexposure, float const Expfactor ) {

	m_linearexpcontrol = Linearexposure;
	m_expfactor = 1.0f / clamp( Expfactor, 1.0f, std::numeric_limits<float>::infinity() );
}

void CSkyDome::SetGammaCorrection( float const Gamma ) {

	m_gammacorrection = 1.0f / clamp( Gamma, std::numeric_limits<float>::epsilon(), std::numeric_limits<float>::infinity() );		
}

void CSkyDome::SetOvercastFactor( float const Overcast ) {

	m_overcast = clamp( Overcast, 0.0f, 1.0f );
}

//******************************************************************************//

void CSkyDome::GetPerez( float *Perez, float Distribution[ 5 ][ 2 ], const float Turbidity ) {

	Perez[ 0 ] = Distribution[ 0 ][ 0 ] * Turbidity + Distribution[ 0 ][ 1 ];
	Perez[ 1 ] = Distribution[ 1 ][ 0 ] * Turbidity + Distribution[ 1 ][ 1 ];
	Perez[ 2 ] = Distribution[ 2 ][ 0 ] * Turbidity + Distribution[ 2 ][ 1 ];
	Perez[ 3 ] = Distribution[ 3 ][ 0 ] * Turbidity + Distribution[ 3 ][ 1 ];
	Perez[ 4 ] = Distribution[ 4 ][ 0 ] * Turbidity + Distribution[ 4 ][ 1 ];
}

float CSkyDome::GetZenith( float Zenithmatrix[ 3 ][ 4 ], const float Theta, const float Turbidity ) {

	const float theta2 = Theta*Theta;
	const float theta3 = Theta*theta2;
	
	return	( Zenithmatrix[0][0] * theta3 + Zenithmatrix[0][1] * theta2 + Zenithmatrix[0][2] * Theta + Zenithmatrix[0][3]) * Turbidity * Turbidity +
			( Zenithmatrix[1][0] * theta3 + Zenithmatrix[1][1] * theta2 + Zenithmatrix[1][2] * Theta + Zenithmatrix[1][3]) * Turbidity +
			( Zenithmatrix[2][0] * theta3 + Zenithmatrix[2][1] * theta2 + Zenithmatrix[2][2] * Theta + Zenithmatrix[2][3]);

}

//******************************************************************************//

float CSkyDome::PerezFunctionO1( float Perezcoeffs[ 5 ], const float Thetasun, const float Zenithval ) {

	const float val = ( 1.0f + Perezcoeffs[ 0 ] * std::exp( Perezcoeffs[ 1 ] ) ) *
						( 1.0f + Perezcoeffs[ 2 ] * std::exp( Perezcoeffs[ 3 ] * Thetasun ) + Perezcoeffs[ 4 ] * std::pow( std::cos( Thetasun ), 2 ) );

	return Zenithval / val;
}

float CSkyDome::PerezFunctionO2( float Perezcoeffs[ 5 ], const float Icostheta, const float Gamma, const float Cosgamma2, const float Zenithval ) {
	// iCosTheta = 1.0f / cosf(theta)
	// cosGamma2 = SQR( cosf( gamma ) )
	return Zenithval * ( 1.0f + Perezcoeffs[ 0 ] * std::exp( Perezcoeffs[ 1 ] * Icostheta ) ) * 
						( 1.0f + Perezcoeffs[ 2 ] * std::exp( Perezcoeffs[ 3 ] * Gamma ) + Perezcoeffs[ 4 ] * Cosgamma2 );
}

//******************************************************************************//
void CSkyDome::RebuildColors() {

	// get zenith luminance
	float const chi = ( (4.0f / 9.0f) - (m_turbidity / 120.0f) ) * ( M_PI - (2.0f * m_thetasun) );
	float zenithluminance = ( (4.0453f * m_turbidity) - 4.9710f ) * std::tan( chi ) - (0.2155f * m_turbidity) + 2.4192f; 

	// get x / y zenith
	float zenithx = GetZenith( m_zenithxmatrix, m_thetasun, m_turbidity );
	float zenithy = GetZenith( m_zenithymatrix, m_thetasun, m_turbidity );

	// get perez function parametrs
	float perezluminance[5], perezx[5], perezy[5];  
	GetPerez( perezluminance, m_distributionluminance, m_turbidity );
	GetPerez( perezx, m_distributionxcomp, m_turbidity );
	GetPerez( perezy, m_distributionycomp, m_turbidity );

	// make some precalculation
	zenithx = PerezFunctionO1( perezx, m_thetasun, zenithx );
	zenithy = PerezFunctionO1( perezy, m_thetasun, zenithy );
	zenithluminance = PerezFunctionO1( perezluminance, m_thetasun, zenithluminance );

    // start with fresh average for the new pass
    float3 averagecolor{ 0.0f, 0.0f, 0.0f };

	// trough all vertices
	float3 vertex;
	float3 color, colorconverter;

	for ( unsigned int i = 0; i < m_vertices.size(); ++i ) {
		// grab it
		vertex = SafeNormalize( m_vertices[ i ] );

		// angle between sun and vertex
		const float gamma = std::acos( DotProduct( vertex, m_sundirection ) );

		// warning : major hack!!! .. i had to do something with values under horizon
		//vertex.y = Clamp<float>( vertex.y, 0.05f, 1.0f );
		if ( vertex.y < 0.05f ) vertex.y = 0.05f;

//		from paper:
//			const float theta = arccos( vertex.y );
//			const float iCosTheta = 1.0f / cosf( theta );
//		optimized:
//			iCosTheta = 
//				= 1.0f / cosf( arccos( vertex.y ) );
//				= 1.0f / vertex.y;
		float const icostheta = 1.0f / vertex.y;
		float const cosgamma2 = std::pow( std::cos( gamma ), 2 );

		// Compute x,y values  
		float const x = PerezFunctionO2( perezx, icostheta, gamma, cosgamma2, zenithx );
		float const y = PerezFunctionO2( perezy, icostheta, gamma, cosgamma2, zenithy );

		// luminance(Y) for clear & overcast sky
		float const yclear = PerezFunctionO2( perezluminance, icostheta, gamma, cosgamma2, zenithluminance );
		float const yover = ( 1.0f + 2.0f * vertex.y ) / 3.0f;
		
		float const Y = interpolate( yclear, yover, m_overcast );
		float const X = (x / y) * Y;  
		float const Z = ((1.0f - x - y) / y) * Y;
		
		colorconverter = float3( X, Y, Z );
		color = XYZtoRGB( colorconverter );

		colorconverter = RGBtoHSV(color);
		if ( m_linearexpcontrol ) {
            // linear scale
			colorconverter.z *= m_expfactor;
		} else {
            // exp scale
			colorconverter.z = 1.0f - exp( -m_expfactor * colorconverter.z );  
		}
		color = HSVtoRGB(colorconverter);
/*
		// gamma control		
		color.x = std::pow( color.x, m_gammacorrection );
		color.x = std::pow( color.y, m_gammacorrection );
		color.x = std::pow( color.z, m_gammacorrection );
*/
        // crude correction for the times where the model breaks (late night)
        // TODO: use proper night sky calculation for these times instead
        if( ( color.x <= 0.0f )
         && ( color.y <= 0.0f ) ) {
            // darken the sky as the sun goes deeper below the horizon
            // 15:50:75 is picture-based night sky colour. it may not be accurate but looks 'right enough'
            color.z = 0.75f * std::max( color.z + m_sundirection.y, 0.075f );
            color.x = 0.20f * color.z; 
            color.y = 0.65f * color.z;
            color = color * ( 1.15f - vertex.y ); // simple gradient, darkening towards the top
        }

		// save
        m_colours[ i ] = color;
        averagecolor += color;
	}

    m_averagecolour = averagecolor / m_vertices.size();
    m_averagecolour.x = std::max( m_averagecolour.x, 0.0f );
    m_averagecolour.y = std::max( m_averagecolour.y, 0.0f );
    m_averagecolour.z = std::max( m_averagecolour.z, 0.0f );
}

//******************************************************************************//