// viewer.hxx -- class for managing a viewer in the flightgear world.
//
// Written by Curtis Olson, started August 1997.
//                          overhaul started October 2000.
//
// Copyright (C) 1997 - 2000  Curtis L. Olson  - curt@flightgear.org
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// This program 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
// 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., 675 Mass Ave, Cambridge, MA 02139, USA.
//
// $Id$


#ifndef _VIEWER_HXX
#define _VIEWER_HXX


#ifndef __cplusplus                                                          
# error This library requires C++
#endif                                   

#include <simgear/compiler.h>
#include <simgear/constants.h>

#include <plib/sg.h>		// plib include

#include "fgfs.hxx"


#define FG_FOV_MIN 0.1
#define FG_FOV_MAX 179.9


/**
 * Representation of a single viewpoint in the FlightGear world.
 */
class FGViewPoint
{
public:
  FGViewPoint ();
  virtual ~FGViewPoint ();

  /**
   * Set the geodetic position for the view point.
   */
  virtual void setPosition (double lon_deg, double lat_deg, double alt_ft);


  /**
   * Get the longitude in degrees.
   */
  virtual double getLongitude_deg () const { return _lon_deg; }

  /**
   * Get the latitude in degrees.
   */
  virtual double getLatitude_deg () const { return _lat_deg; }

  /**
   * Get the altitude in feet ASL.
   */
  virtual double getAltitudeASL_ft () const { return _alt_ft; }

  /**
   * Get the absolute view position in fgfs coordinates.
   */
  virtual const double * getAbsoluteViewPos () const;


  /**
   * Get the relative view position in fgfs coordinates.
   *
   * The position is relative to the scenery centre.
   */
  virtual const float * getRelativeViewPos () const;


  /**
   * Get the absolute zero-elevation view position in fgfs coordinates.
   */
  virtual const float * getZeroElevViewPos () const;

private:

  void recalc () const;

  mutable sgdVec3 _absolute_view_pos;
  mutable sgVec3 _relative_view_pos;
  mutable sgVec3 _zero_elev_view_pos;

  bool _dirty;
  double _lon_deg;
  double _lat_deg;
  double _alt_ft;

};


// Define a structure containing view information
class FGViewer {

public:

    enum fgViewType {
	FG_RPH = 0,
	FG_LOOKAT = 1,
	FG_HPR = 2
    };

    enum fgScalingType {  // nominal Field Of View actually applies to ...
	FG_SCALING_WIDTH,       // window width
	FG_SCALING_MAX,         // max(width, height)
	// FG_SCALING_G_MEAN,      // geometric_mean(width, height)
	// FG_SCALING_INDEPENDENT  // whole screen
    };

private:

    // flag forcing a recalc of derived view parameters
    bool dirty;

protected:

    fgViewType _type;
    fgScalingType scalingType;

    FGViewPoint view_point;

    // the nominal field of view (angle, in degrees)
    double fov; 

    // ratio of window width and height; height = width * aspect_ratio
    double aspect_ratio;

    // the current view offset angle from forward (rotated about the
    // view_up vector)
    double view_offset;
    bool reverse_view_offset;

    // the goal view offset angle  (used for smooth view changes)
    double goal_view_offset;

    // the view tilt angles
    double view_tilt;
    double goal_view_tilt;

    // geodetic view position
    sgdVec3 geod_view_pos;

    // absolute view position in earth coordinates
    sgdVec3 abs_view_pos;

    // view position in opengl world coordinates (this is the
    // abs_view_pos translated to scenery.center)
    sgVec3 view_pos;

    // radius to sea level from center of the earth (m)
    double sea_level_radius;

    // cartesion coordinates of current lon/lat if at sea level
    // translated to scenery.center
    sgVec3 zero_elev;

    // height ASL of the terrain for our current view position
    // (future?) double ground_elev;

    // pilot offset from center of gravity.  The X axis is positive
    // out the tail, Y is out the right wing, and Z is positive up.
    // Distances in meters of course.
    sgVec3 pilot_offset;

    // surface vector heading south
    sgVec3 surface_south;

    // surface vector heading east (used to unambiguously align sky
    // with sun)
    sgVec3 surface_east;

    // world up vector (normal to the plane tangent to the earth's
    // surface at the spot we are directly above
    sgVec3 world_up;

    // sg versions of our friendly matrices
    sgMat4 VIEW, VIEW_ROT, UP;

    inline void set_dirty() { dirty = true; }
    inline void set_clean() { dirty = false; }

    // Update the view volume, position, and orientation
    virtual void update() = 0;

public:

    // Constructor
    FGViewer( void );

    // Destructor
    virtual ~FGViewer( void );

    virtual void init ();
    virtual void bind ();
    virtual void unbind ();
    virtual void update (int dt);

    //////////////////////////////////////////////////////////////////////
    // setter functions
    //////////////////////////////////////////////////////////////////////

    inline void set_fov( double fov_deg ) {
	fov = fov_deg;
    }

    inline void set_aspect_ratio( double r ) {
	aspect_ratio = r;
    }
    inline void set_view_offset( double a ) {
	set_dirty();
	view_offset = a;
    }
    inline void inc_view_offset( double amt ) {
	set_dirty();
	view_offset += amt;
    }
    inline void set_goal_view_offset( double a) {
	set_dirty();
	goal_view_offset = a;
	while ( goal_view_offset < 0.0 ) {
	    goal_view_offset += SGD_2PI;
	}
	while ( goal_view_offset > SGD_2PI ) {
	    goal_view_offset -= SGD_2PI;
	}
    }
    inline void set_reverse_view_offset( bool val ) {
	reverse_view_offset = val;
    }
    inline void set_view_tilt( double a ) {
	set_dirty();
	view_tilt = a;
    }
    inline void inc_view_tilt( double amt ) {
	set_dirty();
	view_tilt += amt;
    }
    inline void set_goal_view_tilt( double a) {
	set_dirty();
	goal_view_tilt = a;
	while ( goal_view_tilt < 0 ) {
	    goal_view_tilt += 360.0;
	}
	while ( goal_view_tilt > 360.0 ) {
	    goal_view_tilt -= 360.0;
	}
    }
    inline void set_geod_view_pos( double lon, double lat, double alt ) {
	// data should be in radians and meters asl
	set_dirty();
	// cout << "set_geod_view_pos = " << lon << ", " << lat << ", " << alt
	//      << endl;
	sgdSetVec3( geod_view_pos, lon, lat, alt );
    }
    inline void set_pilot_offset( float x, float y, float z ) {
	set_dirty();
	sgSetVec3( pilot_offset, x, y, z );
    }
    inline void set_sea_level_radius( double r ) {
	// data should be in meters from the center of the earth
	set_dirty();
	sea_level_radius = r;
    }

    //////////////////////////////////////////////////////////////////////
    // accessor functions
    //////////////////////////////////////////////////////////////////////
    inline int get_type() const { return _type ; }
    inline int is_a( int t ) const { return get_type() == t ; }
    inline bool is_dirty() const { return dirty; }
    inline double get_fov() const { return fov; }
    inline double get_aspect_ratio() const { return aspect_ratio; }
    inline double get_view_offset() const { return view_offset; }
    inline bool get_reverse_view_offset() const { return reverse_view_offset; }
    inline double get_goal_view_offset() const { return goal_view_offset; }
    inline double get_view_tilt() const { return view_tilt; }
    inline double get_goal_view_tilt() const { return goal_view_tilt; }
    inline double *get_geod_view_pos() { return geod_view_pos; }
    inline float *get_pilot_offset() { return pilot_offset; }
    inline double get_sea_level_radius() const { return sea_level_radius; }
    // Get horizontal field of view angle, in degrees.
    double get_h_fov();
    // Get vertical field of view angle, in degrees.
    double get_v_fov();

    //////////////////////////////////////////////////////////////////////
    // derived values accessor functions
    //////////////////////////////////////////////////////////////////////
    inline double *get_abs_view_pos() {
	if ( dirty ) { update(); }
	return abs_view_pos;
    }
    inline float *get_view_pos() {
	if ( dirty ) { update(); }
	return view_pos;
    }
    inline float *get_zero_elev() {
	if ( dirty ) { update(); }
	return zero_elev;
    }
    // (future?)
    // inline double get_ground_elev() {
    //  if ( dirty ) { update(); }
    //	return ground_elev;
    // }
    inline float *get_surface_south() {
	if ( dirty ) { update(); }
	return surface_south;
    }
    inline float *get_surface_east() {
	if ( dirty ) { update(); }
	return surface_east;
    }
    inline float *get_world_up() {
	if ( dirty ) { update(); }
	return world_up;
    }
    inline const sgVec4 *get_VIEW() {
	if ( dirty ) { update(); }
	return VIEW;
    }
    inline const sgVec4 *get_VIEW_ROT() {
	if ( dirty ) { update(); }
	return VIEW_ROT;
    }
    inline const sgVec4 *get_UP() {
	if ( dirty ) { update(); }
	return UP;
    }
};


#endif // _VIEWER_HXX