-// sky.hxx -- ssg based sky model
-//
+/**
+ * \file sky.hxx
+ * Provides a class to model a realistic (time/date/position) based sky.
+ */
+
// Written by Curtis Olson, started December 1997.
// SSG-ified by Curtis Olson, February 2000.
//
typedef layer_list_type::iterator layer_list_iterator;
typedef layer_list_type::const_iterator layer_list_const_iterator;
+/**
+ * A class to model a realistic (time/date/position) based sky.
+ *
+ * Introduction
+ *
+ * The SGSky class models a blended sky dome, a haloed sun, a textured
+ * moon with phase that properly matches the date, stars and planets,
+ * and cloud layers. SGSky is designed to be dropped into existing
+ * plib based applications and depends heavily on plib's scene graph
+ * library, ssg. The sky implements various time of day lighting
+ * effects, it plays well with fog and visibility effects, and
+ * implements scudded cloud fly-through effects. Additionally, you can
+ * wire in the output of the SGEphemeris class to accurately position
+ * all the objects in the sky.
+ *
+ * Building the sky
+ *
+
+ * Once you have created an instance of SGSky you must call the
+ * build() method. Building the sky requires several textures. So,
+ * you must specify the path/directory where these textures reside
+ * before building the sky. You do this first by calling the
+ * texture_path() method.
+
+ * The arguments you pass to the build() method allow you to specify
+ * the size of your sun sphere and moon sphere, a number of planets,
+ * and a multitude of stars. For the planets and stars you pass in an
+ * array of right ascensions, declinations, magnitudes, and the
+ * distance from the view point.
+
+ * Cloud Layers
+
+ * Cloud layers can be added, changed, or removed individually. To add
+ * a cloud layer use the add_cloud_layer() method. The arguments
+ * allow you to specify base height above sea level, layer thickness,
+ * a transition zone for entering/leaving the cloud layer, the size of
+ * the cloud object, and the type of cloud texture. All distances are
+ * in meters. There are additional forms of this method that allow you
+ * to specify your own ssgSimpleState or texture name for drawing the
+ * cloud layer.
+
+ * Repainting the Sky
+
+ * As the sun circles the globe, you can call the repaint() method to
+ * recolor the sky objects to simulate sunrise and sunset effects,
+ * visibility, and other lighting changes. The arguments allow you to
+ * specify a base sky color (for the top of the dome), a fog color
+ * (for the horizon), the sun angle with the horizon (for
+ * sunrise/sunset effects), the moon angle (so we can make it more
+ * yellow at the horizon), and new star and planet data so that we can
+ * optionally change the magnitude of these (for day / night
+ * transitions.)
+
+ * Positioning Sky Objects
+
+ * As time progresses and as you move across the surface of the earth,
+ * the apparent position of the objects and the various lighting
+ * effects can change. the reposition() method allows you to specify
+ * the positions of all the sky objects as well as your view position.
+ * The arguments allow you to specify your view position in world
+ * Cartesian coordinates, the zero elevation position in world
+ * Cartesian coordinates (your longitude, your latitude, sea level),
+ * the ``up'' vector in world Cartesian coordinates, current
+ * longitude, latitude, and altitude. A ``spin'' angle can be
+ * specified for orienting the sky with the sun position so sunset and
+ * sunrise effects look correct. You must specify GMT side real time,
+ * the sun right ascension, sun declination, and sun distance from
+ * view point (to keep it inside your view volume.) You also must
+ * specify moon right ascension, moon declination, and moon distance
+ * from view point.
+
+ * Rendering the Sky
+
+ * The sky is designed to be rendered in two stages. The first stage
+ * renders the parts that form your back drop - the sky dome, the
+ * stars and planets, the sun, and the moon. These should be rendered
+ * before the rest of your scene by calling the preDraw() method. The
+ * second stage renders the clouds which are likely to be translucent
+ * (depending on type) and should be drawn after your scene has been
+ * rendered. Use the postDraw() method to draw the second stage of
+ * the sky.
+
+ * A typical application might do the following:
+
+ * <li> thesky->preDraw();
+ * <li> ssgCullAndDraw ( myscene ) ;
+ * <li> thesky->postDraw( my_altitude );
+
+ * The current altitude in meters is passed to the postDraw() method
+ * so the clouds layers can be rendered correction from most distant
+ * to closest.
+
+ * Visibility Effects
+
+ * Visibility and fog is important for correctly rendering the
+ * sky. You can inform SGSky of the current visibility by calling the
+ * set_visibility() method.
+
+ * When transitioning through clouds, it is nice to pull in the fog as
+ * you get close to the cloud layer to hide the fact that the clouds
+ * are drawn as a flat polygon. As you get nearer to the cloud layer
+ * it is also nice to temporarily pull in the visibility to simulate
+ * the effects of flying in and out of the puffy edge of the
+ * cloud. These effects can all be accomplished by calling the
+ * modify_vis() method. The arguments allow you to specify your
+ * current altitude (which is then compared to the altitudes of the
+ * various cloud layers.) You can also specify a time factor which
+ * should be the length in seconds since the last time you called
+ * modify_vis(). The time_factor value allows the puffy cloud effect
+ * to be calculated correctly.
+
+ * The modify_vis() method alters the SGSky's internal idea of
+ * visibility, so you should subsequently call get_visibility() to get
+ * the actual modified visibility. You should then make the
+ * appropriate glFog() calls to setup fog properly for your scene.
+
+ * Accessor Methods
+
+ * Once an instance of SGSky has been successfully initialized, there
+ * are a couple accessor methods you can use such as get_num_layers()
+ * to return the number of cloud layers, get_cloud_layer(i) to return
+ * cloud layer number i, get_visibility() to return the actual
+ * visibility as modified by the sky/cloud model.
+
+ */
class SGSky {
public:
- // Constructor
+ /** Constructor */
SGSky( void );
- // Destructor
+ /** Destructor */
~SGSky( void );
- // initialize the sky and connect the components to the scene
- // graph at the provided branch
+ /**
+ * Initialize the sky and connect the components to the scene
+ * graph at the provided branch. See discussion in detailed class
+ * description.
+ * @param sun_size size of sun
+ * @param moon_size size of moon
+ * @param nplanets number of planets
+ * @param planet_data an array of planet right ascensions, declinations,
+ * and magnitudes
+ * @param planet_dist distance from viewer to put the planets
+ * @param nstars number of stars
+ * @param star_data an array of star right ascensions, declinations,
+ * and magnitudes
+ * @param star_dist distance from viewer to put the stars */
void build( double sun_size, double moon_size,
int nplanets, sgdVec3 *planet_data, double planet_dist,
int nstars, sgdVec3 *star_data, double star_dist );
- // repaint the sky components based on current value of sun_angle,
- // sky, and fog colors.
- //
- // sun angle in degrees relative to verticle
- // 0 degrees = high noon
- // 90 degrees = sun rise/set
- // 180 degrees = darkest midnight
+ /**
+ * Repaint the sky components based on current value of sun_angle,
+ * sky, and fog colors. You can also specify new star and planet
+ * data so that we can optionally change the magnitude of these
+ * (for day/night transitions.) See discussion in detailed
+ * class description.
+ *
+ * Sun and moon angles are specified in degrees relative to local up
+ * <li> 0 degrees = high noon
+ * <li> 90 degrees = sun rise/set
+ * <li> 180 degrees = darkest midnight
+ * @param sky_color the base sky color (for the top of the dome)
+ * @param fog_color the fog color (for the horizon)
+ * @param sun_angle the sun angle with the horizon (for sunrise/sunset
+ * effects)
+ * @param moon_angle the moon angle (so we can make it more yellow
+ * at the horizon)
+ * @param nplanets number of planets
+ * @param planet_data an array of planet right ascensions, declinations,
+ * and magnitudes
+ * @param nstars number of stars
+ * @param star_data an array of star right ascensions, declinations,
+ * and magnitudes
+ */
bool repaint( sgVec4 sky_color, sgVec4 fog_color,
double sun_angle, double moon_angle,
int nplanets, sgdVec3 *planet_data,
int nstars, sgdVec3 *star_data );
- // reposition the sky at the specified origin and orientation
- //
- // lon specifies a rotation about the Z axis
- // lat specifies a rotation about the new Y axis
- // spin specifies a rotation about the new Z axis (this allows
- // additional orientation for the sunrise/set effects and is used
- // by the skydome and perhaps clouds.
+ /**
+ * Reposition the sky at the specified origin and orientation
+ *
+ * lon specifies a rotation about the Z axis
+ * lat specifies a rotation about the new Y axis
+ * spin specifies a rotation about the new Z axis (this allows
+ * additional orientation for the sunrise/set effects and is used
+ * by the skydome and perhaps clouds. See discussion in detailed
+ * class description.
+ * @param view_pos specify your view position in world Cartesian
+ * coordinates
+ * @param zero_elev the zero elevation position in world Cartesian
+ * coordinates
+ * @param view_up the up vector in world Cartesian coordinates
+ * @param lon current longitude
+ * @param lat current latitude
+ * @param alt current altitude
+ * @param spin an offset angle for orienting the sky effects with the
+ * sun position so sunset and sunrise effects look correct.
+ * @param gst GMT side real time
+ * @param sun_ra the sun's current right ascension
+ * @param sun_dec the sun's current declination
+ * @param sun_dist the sun's distance from the current view point
+ * (to keep it inside your view volume.)
+ * @param moon_ra the moon's current right ascension
+ * @param moon_dec the moon's current declination
+ * @param moon_dist the moon's distance from the current view point.
+ */
bool reposition( sgVec3 view_pos, sgVec3 zero_elev, sgVec3 view_up,
double lon, double lat, double alt, double spin,
double gst,
double sun_ra, double sun_dec, double sun_dist,
double moon_ra, double moon_dec, double moon_dist );
- // modify the given visibility based on cloud layers, thickness,
- // transition range, and simulated "puffs".
+ /**
+ * Modify the given visibility based on cloud layers, thickness,
+ * transition range, and simulated "puffs". See discussion in detailed
+ * class description.
+ * @param alt current altitude
+ * @param time_factor amount of time since modify_vis() last called so
+ * we can scale effect rates properly despite variable frame rates.
+ */
void modify_vis( float alt, float time_factor );
- // draw background portions of the sky ... do this before you draw
- // the rest of your scene.
+ /**
+ * Draw background portions of the sky ... do this before you draw
+ * the rest of your scene. See discussion in detailed
+ * class description.
+ */
void preDraw();
- // draw translucent clouds ... do this after you've drawn all the
- // oapaque elements of your scene.
+ /**
+ * Draw translucent clouds ... do this after you've drawn all the
+ * oapaque elements of your scene. See discussion in detailed
+ * class description.
+ * @param alt current altitude
+ */
void postDraw( float alt );
- // specify the texture path (optional, defaults to current directory)
+ /**
+ * Specify the texture path (optional, defaults to current directory)
+ * @param path base path to texture locations
+ */
inline void texture_path( const string& path ) {
tex_path = SGPath( path );
}
- // enable the sky
+ /** Enable drawing of the sky. */
inline void enable() {
pre_selector->select( 1 );
post_selector->select( 1 );
}
- // disable the sky in the scene graph. The leaf node is still
- // there, how ever it won't be traversed on by ssgCullandRender()
+ /**
+ * Disable drawing of the sky in the scene graph. The leaf node is still
+ * there, how ever it won't be traversed on by ssgCullandRender()
+ */
inline void disable() {
pre_selector->select( 0 );
post_selector->select( 0 );
}
- // add a cloud layer (above sea level in meters)
+ /**
+ * Add a cloud layer (distances in meters).
+ * @param asl cloud base height above sea level
+ * @param thickness cloud layer thickness
+ * @param transition thickness of transition layer from 100% out of
+ * cloud to 100% in cloud. Used for scudded clouds effect.
+ * @param span horizontal size of cloud object
+ * @param type type of cloud (chosen from available cloud types)
+ */
void add_cloud_layer( double asl, double thickness,
double transition, double span,
SGCloudType type );
+
+ /**
+ * Add a cloud layer (distances in meters).
+ * @param asl cloud base height above sea level
+ * @param thickness cloud layer thickness
+ * @param transition thickness of transition layer from 100% out of
+ * cloud to 100% in cloud. Used for scudded clouds effect.
+ * @param span horizontal size of cloud object
+ * @param tex_path file name of a cloud texture
+ */
void add_cloud_layer( double asl, double thickness,
double transition, double span,
const string &tex_path );
+
+ /**
+ * Add a cloud layer (distances in meters).
+ * @param asl cloud base height above sea level
+ * @param thickness cloud layer thickness
+ * @param transition thickness of transition layer from 100% out of
+ * cloud to 100% in cloud. Used for scudded clouds effect.
+ * @param span horizontal size of cloud object
+ * @param state pointer to an existing ssgSimpleState
+ */
void add_cloud_layer( double asl, double thickness,
double transition, double span,
ssgSimpleState *state );
+ /** @return number of cloud layers */
inline int get_num_layers() const { return cloud_layers.size(); }
+
+ /**
+ * Get a cloud layer
+ * @param i which cloud layer
+ * @return cloud layer number i */
inline SGCloudLayer *get_cloud_layer( int i ) const {
return cloud_layers[i];
}
+ /** @return current effective visibility */
inline float get_visibility() const { return effective_visibility; }
+
+ /** Set desired clear air visibility.
+ * @param v visibility in meters
+ */
inline void set_visibility( float v ) {
effective_visibility = visibility = v;
}
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