// oursun.hxx -- model earth's sun
//
// Written by Durk Talsma. Originally started October 1997, for distribution  
// with the FlightGear project. Version 2 was written in August and 
// September 1998. This code is based upon algorithms and data kindly 
// provided by Mr. Paul Schlyter. (pausch@saaf.se). 
//
// Separated out rendering pieces and converted to ssg by Curt Olson,
// March 2000
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Library General Public
// License as published by the Free Software Foundation; either
// version 2 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Library General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
//
// $Id: oursun.cxx,v 1.24 2007-12-22 23:01:36 timoore Exp $


#ifdef HAVE_CONFIG_H
#  include <simgear_config.h>
#endif

#include <simgear/compiler.h>

#include <osg/AlphaFunc>
#include <osg/BlendFunc>
#include <osg/Fog>
#include <osg/Geode>
#include <osg/Geometry>
#include <osg/Material>
#include <osg/ShadeModel>
#include <osg/TexEnv>
#include <osg/Texture2D>
#include <osgDB/ReadFile>

#include <simgear/misc/PathOptions.hxx>
#include <simgear/screen/colors.hxx>
#include <simgear/scene/model/model.hxx>
#include "oursun.hxx"

using namespace simgear;

// Constructor
SGSun::SGSun( void ) :
    visibility(-9999.0), prev_sun_angle(-9999.0), path_distance(60000.0),
    sun_exp2_punch_through(7.0e-06)
{

}


// Destructor
SGSun::~SGSun( void ) {
}


// initialize the sun object and connect it into our scene graph root
osg::Node*
SGSun::build( SGPath path, double sun_size, SGPropertyNode *property_tree_Node ) {

    env_node = property_tree_Node;

    osg::ref_ptr<osgDB::ReaderWriter::Options> options
        = makeOptionsFromPath(path);
    // build the ssg scene graph sub tree for the sky and connected
    // into the provide scene graph branch
    sun_transform = new osg::MatrixTransform;
    osg::StateSet* stateSet = sun_transform->getOrCreateStateSet();

    osg::TexEnv* texEnv = new osg::TexEnv;
    texEnv->setMode(osg::TexEnv::MODULATE);
    stateSet->setTextureAttribute(0, texEnv, osg::StateAttribute::ON);
 
    osg::Material* material = new osg::Material;
    material->setColorMode(osg::Material::AMBIENT_AND_DIFFUSE);
    material->setEmission(osg::Material::FRONT_AND_BACK,
                          osg::Vec4(0, 0, 0, 1));
    material->setSpecular(osg::Material::FRONT_AND_BACK,
                          osg::Vec4(0, 0, 0, 1));
    stateSet->setAttribute(material);

    osg::ShadeModel* shadeModel = new osg::ShadeModel;
    shadeModel->setMode(osg::ShadeModel::SMOOTH);
    stateSet->setAttributeAndModes(shadeModel);

    osg::AlphaFunc* alphaFunc = new osg::AlphaFunc;
    alphaFunc->setFunction(osg::AlphaFunc::ALWAYS);
    stateSet->setAttributeAndModes(alphaFunc);

    osg::BlendFunc* blendFunc = new osg::BlendFunc;
    blendFunc->setSource(osg::BlendFunc::SRC_ALPHA);
    blendFunc->setDestination(osg::BlendFunc::ONE_MINUS_SRC_ALPHA);
    stateSet->setAttributeAndModes(blendFunc);

    stateSet->setMode(GL_FOG, osg::StateAttribute::OFF);
    stateSet->setMode(GL_LIGHTING, osg::StateAttribute::OFF);
    stateSet->setMode(GL_CULL_FACE, osg::StateAttribute::OFF);
    stateSet->setMode(GL_DEPTH_TEST, osg::StateAttribute::OFF);

    osg::Geode* geode = new osg::Geode;
    stateSet = geode->getOrCreateStateSet();

    stateSet->setRenderBinDetails(-6, "RenderBin");

    // set up the sun-state
    osg::Texture2D* texture = SGLoadTexture2D("sun.rgba", options.get());
    stateSet->setTextureAttributeAndModes(0, texture);

    // Build scenegraph
    sun_cl = new osg::Vec4Array;
    sun_cl->push_back(osg::Vec4(1, 1, 1, 1));

    osg::Vec3Array* sun_vl = new osg::Vec3Array;
    sun_vl->push_back(osg::Vec3(-sun_size, 0, -sun_size));
    sun_vl->push_back(osg::Vec3(sun_size, 0, -sun_size));
    sun_vl->push_back(osg::Vec3(-sun_size, 0, sun_size));
    sun_vl->push_back(osg::Vec3(sun_size, 0, sun_size));

    osg::Vec2Array* sun_tl = new osg::Vec2Array;
    sun_tl->push_back(osg::Vec2(0, 0));
    sun_tl->push_back(osg::Vec2(1, 0));
    sun_tl->push_back(osg::Vec2(0, 1));
    sun_tl->push_back(osg::Vec2(1, 1));

    osg::Geometry* geometry = new osg::Geometry;
    geometry->setUseDisplayList(false);
    geometry->setVertexArray(sun_vl);
    geometry->setColorArray(sun_cl.get());
    geometry->setColorBinding(osg::Geometry::BIND_OVERALL);
    geometry->setNormalBinding(osg::Geometry::BIND_OFF);
    geometry->setTexCoordArray(0, sun_tl);
    geometry->addPrimitiveSet(new osg::DrawArrays(GL_TRIANGLE_STRIP, 0, 4));
    geode->addDrawable(geometry);

    sun_transform->addChild( geode );

    // set up the inner-halo state
    geode = new osg::Geode;
    stateSet = geode->getOrCreateStateSet();
    stateSet->setRenderBinDetails(-7, "RenderBin");
    
    texture = SGLoadTexture2D("inner_halo.rgba", options.get());
    stateSet->setTextureAttributeAndModes(0, texture);

    // Build ssg structure
    ihalo_cl = new osg::Vec4Array;
    ihalo_cl->push_back(osg::Vec4(1, 1, 1, 1));

    float ihalo_size = sun_size * 2.0;
    osg::Vec3Array* ihalo_vl = new osg::Vec3Array;
    ihalo_vl->push_back(osg::Vec3(-ihalo_size, 0, -ihalo_size));
    ihalo_vl->push_back(osg::Vec3(ihalo_size, 0, -ihalo_size));
    ihalo_vl->push_back(osg::Vec3(-ihalo_size, 0, ihalo_size));
    ihalo_vl->push_back(osg::Vec3(ihalo_size, 0, ihalo_size));

    osg::Vec2Array* ihalo_tl = new osg::Vec2Array;
    ihalo_tl->push_back(osg::Vec2(0, 0));
    ihalo_tl->push_back(osg::Vec2(1, 0));
    ihalo_tl->push_back(osg::Vec2(0, 1));
    ihalo_tl->push_back(osg::Vec2(1, 1));

    geometry = new osg::Geometry;
    geometry->setUseDisplayList(false);
    geometry->setVertexArray(ihalo_vl);
    geometry->setColorArray(ihalo_cl.get());
    geometry->setColorBinding(osg::Geometry::BIND_OVERALL);
    geometry->setNormalBinding(osg::Geometry::BIND_OFF);
    geometry->setTexCoordArray(0, ihalo_tl);
    geometry->addPrimitiveSet(new osg::DrawArrays(GL_TRIANGLE_STRIP, 0, 4));
    geode->addDrawable(geometry);

    sun_transform->addChild( geode );
    
    // set up the outer halo state
    
    geode = new osg::Geode;
    stateSet = geode->getOrCreateStateSet();
    stateSet->setRenderBinDetails(-8, "RenderBin");

    texture = SGLoadTexture2D("outer_halo.rgba", options.get());
    stateSet->setTextureAttributeAndModes(0, texture);

    // Build ssg structure
    ohalo_cl = new osg::Vec4Array;
    ohalo_cl->push_back(osg::Vec4(1, 1, 1, 1));

    double ohalo_size = sun_size * 8.0;
    osg::Vec3Array* ohalo_vl = new osg::Vec3Array;
    ohalo_vl->push_back(osg::Vec3(-ohalo_size, 0, -ohalo_size));
    ohalo_vl->push_back(osg::Vec3(ohalo_size, 0, -ohalo_size));
    ohalo_vl->push_back(osg::Vec3(-ohalo_size, 0, ohalo_size));
    ohalo_vl->push_back(osg::Vec3(ohalo_size, 0, ohalo_size));

    osg::Vec2Array* ohalo_tl = new osg::Vec2Array;
    ohalo_tl->push_back(osg::Vec2(0, 0));
    ohalo_tl->push_back(osg::Vec2(1, 0));
    ohalo_tl->push_back(osg::Vec2(0, 1));
    ohalo_tl->push_back(osg::Vec2(1, 1));

    geometry = new osg::Geometry;
    geometry->setUseDisplayList(false);
    geometry->setVertexArray(ohalo_vl);
    geometry->setColorArray(ohalo_cl.get());
    geometry->setColorBinding(osg::Geometry::BIND_OVERALL);
    geometry->setNormalBinding(osg::Geometry::BIND_OFF);
    geometry->setTexCoordArray(0, ohalo_tl);
    geometry->addPrimitiveSet(new osg::DrawArrays(GL_TRIANGLE_STRIP, 0, 4));
    geode->addDrawable(geometry);

    sun_transform->addChild( geode );


    // force a repaint of the sun colors with arbitrary defaults
    repaint( 0.0, 1.0 );

    return sun_transform.get();
}


// repaint the sun colors based on current value of sun_angle in
// degrees relative to verticle
// 0 degrees = high noon
// 90 degrees = sun rise/set
// 180 degrees = darkest midnight
bool SGSun::repaint( double sun_angle, double new_visibility ) {
    
	if ( visibility != new_visibility ) {
        	visibility = new_visibility;

        	static const double sqrt_m_log01 = sqrt( -log( 0.01 ) );
        	sun_exp2_punch_through = sqrt_m_log01 / ( visibility * 15 );
    	}

    	if ( prev_sun_angle != sun_angle ) {
        	prev_sun_angle = sun_angle;

		// determine how much aerosols are in the air (rough guess)
		double aerosol_factor;
		if ( visibility < 100 ){
        		aerosol_factor = 8000;
		}
		else {
        		aerosol_factor = 80.5 / log( visibility / 100 );
		}

		// get environmental data from property tree or use defaults
		double rel_humidity, density_avg;

		if ( !env_node )
		{
			rel_humidity = 0.5;
			density_avg = 0.7;
		}
		else
		{
			rel_humidity = env_node->getFloatValue( "relative-humidity" ); 
			density_avg =  env_node->getFloatValue( "atmosphere/density-tropo-avg" );
		}

		// ok, now let's go and generate the sun color
                osg::Vec4 i_halo_color, o_halo_color, sun_color;

		// Some comments: 
		// When the sunangle changes, light has to travel a longer distance through the atmosphere.
		// So it's scattered more due to raleigh scattering, which affects blue more than green light.
		// Red is almost not scattered and effectively only get's touched when the sun is near the horizon.
		// Visability also affects suncolor inasmuch as more particles are in the air that cause more scattering.
		// We base our calculation on the halo's color, which is most scattered. 
 
		// Red - is almost not scattered 	
		// Lambda is 700 nm
		
		double red_scat_f = ( aerosol_factor * path_distance * density_avg ) / 5E+07;
		sun_color[0] = 1 - red_scat_f;
		i_halo_color[0] = 1 - ( 1.1 * red_scat_f );
		o_halo_color[0] = 1 - ( 1.4 * red_scat_f );

		// Green - 546.1 nm
		double green_scat_f = ( aerosol_factor * path_distance * density_avg ) / 8.8938E+06;
		sun_color[1] = 1 - green_scat_f;
		i_halo_color[1] = 1 - ( 1.1 * green_scat_f );
		o_halo_color[1] = 1 - ( 1.4 * green_scat_f );
 
		// Blue - 435.8 nm
		double blue_scat_f = ( aerosol_factor * path_distance * density_avg ) / 3.607E+06;
		sun_color[2] = 1 - blue_scat_f;
		i_halo_color[2] = 1 - ( 1.1 * blue_scat_f );
		o_halo_color[2] = 1 - ( 1.4 * blue_scat_f );

		// Alpha
		sun_color[3] = 1;
		i_halo_color[3] = 1;

		o_halo_color[3] = blue_scat_f; 
		if ( ( new_visibility < 10000 ) &&  ( blue_scat_f > 1 )){
			o_halo_color[3] = 2 - blue_scat_f; 
		}


		// Now that we have the color calculated 
		// let's consider the saturation which is produced by mie scattering
		double saturation = 1 - ( rel_humidity / 200 );
		sun_color[1] += (( 1 - saturation ) * ( 1 - sun_color[1] ));
		sun_color[2] += (( 1 - saturation ) * ( 1 - sun_color[2] ));

		i_halo_color[1] += (( 1 - saturation ) * ( 1 - i_halo_color[1] ));
		i_halo_color[2] += (( 1 - saturation ) * ( 1 - i_halo_color[2] )); 

		o_halo_color[1] += (( 1 - saturation ) * ( 1 - o_halo_color[1] )); 
		o_halo_color[2] += (( 1 - saturation ) * ( 1 - o_halo_color[2] )); 

		// just to make sure we're in the limits
		if ( sun_color[0] < 0 ) sun_color[0] = 0;
		else if ( sun_color[0] > 1) sun_color[0] = 1;
		if ( i_halo_color[0] < 0 ) i_halo_color[0] = 0;
		else if ( i_halo_color[0] > 1) i_halo_color[0] = 1;
		if ( o_halo_color[0] < 0 ) o_halo_color[0] = 0;
		else if ( o_halo_color[0] > 1) o_halo_color[0] = 1;

		if ( sun_color[1] < 0 ) sun_color[1] = 0;
		else if ( sun_color[1] > 1) sun_color[1] = 1;
		if ( i_halo_color[1] < 0 ) i_halo_color[1] = 0;
		else if ( i_halo_color[1] > 1) i_halo_color[1] = 1;
		if ( o_halo_color[1] < 0 ) o_halo_color[1] = 0;
		else if ( o_halo_color[1] > 1) o_halo_color[1] = 1;

		if ( sun_color[2] < 0 ) sun_color[2] = 0;
		else if ( sun_color[2] > 1) sun_color[2] = 1;
		if ( i_halo_color[2] < 0 ) i_halo_color[2] = 0;
		else if ( i_halo_color[2] > 1) i_halo_color[2] = 1;
		if ( o_halo_color[2] < 0 ) o_halo_color[2] = 0;
		else if ( o_halo_color[2] > 1) o_halo_color[2] = 1;
		if ( o_halo_color[3] < 0 ) o_halo_color[3] = 0;
		else if ( o_halo_color[3] > 1) o_halo_color[3] = 1;

        
		gamma_correct_rgb( i_halo_color._v );
		gamma_correct_rgb( o_halo_color._v );
		gamma_correct_rgb( sun_color._v );	

        	(*sun_cl)[0] = sun_color;
                sun_cl->dirty();
        	(*ihalo_cl)[0] = i_halo_color;
                ihalo_cl->dirty();
        	(*ohalo_cl)[0] = o_halo_color;
                ohalo_cl->dirty();
    }

    return true;
}


// reposition the sun at the specified right ascension and
// declination, offset by our current position (p) so that it appears
// fixed at a great distance from the viewer.  Also add in an optional
// rotation (i.e. for the current time of day.)
// Then calculate stuff needed for the sun-coloring
bool SGSun::reposition( const SGVec3f& p, double angle,
			double rightAscension, double declination, 
			double sun_dist, double lat, double alt_asl, double sun_angle)
{
    // GST - GMT sidereal time 
    osg::Matrix T1, T2, GST, RA, DEC;

    T1.makeTranslate(p.osg());
    GST.makeRotate(SGD_DEGREES_TO_RADIANS*angle, osg::Vec3(0, 0, -1));

    // xglRotatef( ((SGD_RADIANS_TO_DEGREES * rightAscension)- 90.0),
    //             0.0, 0.0, 1.0);
    RA.makeRotate(rightAscension - 90*SGD_DEGREES_TO_RADIANS, osg::Vec3(0, 0, 1));

    // xglRotatef((SGD_RADIANS_TO_DEGREES * declination), 1.0, 0.0, 0.0);
    DEC.makeRotate(declination, osg::Vec3(1, 0, 0));

    // xglTranslatef(0,sun_dist);
    T2.makeTranslate(osg::Vec3(0, sun_dist, 0));

    sun_transform->setMatrix(T2*DEC*RA*GST*T1);

    // Suncolor related things:
    if ( prev_sun_angle != sun_angle ) {
      if ( sun_angle == 0 ) sun_angle = 0.1;
         const double r_earth_pole = 6356752.314;
         const double r_tropo_pole = 6356752.314 + 8000;
         const double epsilon_earth2 = 6.694380066E-3;
         const double epsilon_tropo2 = 9.170014946E-3;

         double r_tropo = r_tropo_pole / sqrt ( 1 - ( epsilon_tropo2 * pow ( cos( lat ), 2 )));
         double r_earth = r_earth_pole / sqrt ( 1 - ( epsilon_earth2 * pow ( cos( lat ), 2 )));
 
         double position_radius = r_earth + alt_asl;

         double gamma =  SG_PI - sun_angle;
         double sin_beta =  ( position_radius * sin ( gamma )  ) / r_tropo;
         double alpha =  SG_PI - gamma - asin( sin_beta );

         // OK, now let's calculate the distance the light travels
         path_distance = sqrt( pow( position_radius, 2 ) + pow( r_tropo, 2 )
                        - ( 2 * position_radius * r_tropo * cos( alpha ) ));

         double alt_half = sqrt( pow ( r_tropo, 2 ) + pow( path_distance / 2, 2 ) - r_tropo * path_distance * cos( asin( sin_beta )) ) - r_earth;

         if ( alt_half < 0.0 ) alt_half = 0.0;

         // Push the data to the property tree, so it can be used in the enviromental code
         if ( env_node ){
            env_node->setDoubleValue( "atmosphere/altitude-troposphere-top", r_tropo - r_earth );
            env_node->setDoubleValue( "atmosphere/altitude-half-to-sun", alt_half );
      }
    }

    return true;
}

SGVec4f
SGSun::get_color()
{
    return SGVec4f((*sun_cl)[0][0], (*sun_cl)[0][1], (*sun_cl)[0][2], (*sun_cl)[0][3]);
}
