A class to model a realistic (time/date/position) based sky. More...
#include <sky.hxx>
Public Member Functions | |
| SGSky (void) | |
| Constructor. | |
| ~SGSky (void) | |
| Destructor. | |
| void | build (double h_radius_m, double v_radius_m, double sun_size, double moon_size, const SGEphemeris &eph, SGPropertyNode *property_tree_node) |
| Initialize the sky and connect the components to the scene graph at the provided branch. | |
| bool | repaint (const SGSkyColor &sc, const SGEphemeris &eph) |
| Repaint the sky components based on current value of sun_angle, sky, and fog colors. | |
| bool | reposition (const SGSkyState &st, const SGEphemeris &eph, double dt=0.0) |
| Reposition the sky at the specified origin and orientation. | |
| void | modify_vis (float alt, float time_factor) |
| Modify the given visibility based on cloud layers, thickness, transition range, and simulated "puffs". | |
| void | texture_path (const string &path) |
| Specify the texture path (optional, defaults to current directory). | |
| void | enable () |
| Enable drawing of the sky. | |
| void | disable () |
| Disable drawing of the sky in the scene graph. | |
| SGVec4f | get_sun_color () |
| Get the current sun color. | |
| SGVec4f | get_scene_color () |
| Get the current scene color. | |
| void | add_cloud_layer (SGCloudLayer *layer) |
| Add a cloud layer. | |
| const SGCloudLayer * | get_cloud_layer (int i) const |
| Get a cloud layer (const). | |
| SGCloudLayer * | get_cloud_layer (int i) |
| Get a cloud layer (non-const). | |
| int | get_cloud_layer_count () const |
| Return the number of cloud layers currently available. | |
| float | get_visibility () const |
| void | set_visibility (float v) |
| Set desired clear air visibility. | |
| virtual double | get_3dCloudDensity () const |
| Get 3D cloud density. | |
| virtual void | set_3dCloudDensity (double density) |
| Set 3D cloud density. | |
| virtual float | get_3dCloudVisRange () const |
| Get 3D cloud visibility range. | |
| virtual void | set_3dCloudVisRange (float vis) |
| Set 3D cloud visibility range. | |
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 horizontal and vertical radiuses of the sky dome, 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, and magnitudes.
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 three 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 that are above the viewer. This stage is done before translucent objects in the main scene are drawn. It is seperated from the preDraw routine to enable to implement a multi passes technique and is located in the drawUpperClouds() method. The third stage renders the clouds that are below the viewer an which are likely to be translucent (depending on type) and should be drawn after your scene has been rendered. Use the drawLowerClouds() method to draw the second stage of the sky.
A typical application might do the following:
thesky->preDraw( my_altitude ); thesky->drawUpperClouds(); ssgCullAndDraw ( myscene ) ; thesky->drawLowerClouds();
The current altitude in meters is passed to the preDraw() 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.
Definition at line 209 of file sky.hxx.
| void SGSky::add_cloud_layer | ( | SGCloudLayer * | layer | ) |
| void SGSky::build | ( | double | h_radius_m, | |
| double | v_radius_m, | |||
| double | sun_size, | |||
| double | moon_size, | |||
| const SGEphemeris & | eph, | |||
| SGPropertyNode * | property_tree_node | |||
| ) |
Initialize the sky and connect the components to the scene graph at the provided branch.
See discussion in detailed class description.
| h_radius_m | horizontal radius of sky dome | |
| v_radius_m | vertical radius of sky dome | |
| sun_size | size of sun | |
| moon_size | size of moon | |
| nplanets | number of planets | |
| planet_data | an array of planet right ascensions, declinations, and magnitudes | |
| nstars | number of stars | |
| star_data | an array of star right ascensions, declinations, and magnitudes |
| void SGSky::disable | ( | ) | [inline] |
| SGCloudLayer * SGSky::get_cloud_layer | ( | int | i | ) |
| const SGCloudLayer * SGSky::get_cloud_layer | ( | int | i | ) | const |
| int SGSky::get_cloud_layer_count | ( | ) | const |
| float SGSky::get_visibility | ( | ) | const [inline] |
| void SGSky::modify_vis | ( | float | alt, | |
| float | time_factor | |||
| ) |
Modify the given visibility based on cloud layers, thickness, transition range, and simulated "puffs".
See discussion in detailed class description.
| alt | current altitude | |
| time_factor | amount of time since modify_vis() last called so we can scale effect rates properly despite variable frame rates. |
| bool SGSky::repaint | ( | const SGSkyColor & | sc, | |
| const SGEphemeris & | eph | |||
| ) |
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 0 degrees = high noon 90 degrees = sun rise/set 180 degrees = darkest midnight
| sky_color | the base sky color (for the top of the dome) | |
| fog_color | the fog color (for the horizon) | |
| sun_angle | the sun angle with the horizon (for sunrise/sunset effects) | |
| moon_angle | the moon angle (so we can make it more yellow at the horizon) | |
| nplanets | number of planets | |
| planet_data | an array of planet right ascensions, declinations, and magnitudes | |
| nstars | number of stars | |
| star_data | an array of star right ascensions, declinations, and magnitudes |
| bool SGSky::reposition | ( | const SGSkyState & | st, | |
| const SGEphemeris & | eph, | |||
| double | dt = 0.0 | |||
| ) |
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.
| view_pos | specify your view position in world Cartesian coordinates | |
| zero_elev | the zero elevation position in world Cartesian coordinates | |
| view_up | the up vector in world Cartesian coordinates | |
| lon | current longitude | |
| lat | current latitude | |
| alt | current altitude | |
| spin | an offset angle for orienting the sky effects with the sun position so sunset and sunrise effects look correct. | |
| gst | GMT side real time | |
| sun_ra | the sun's current right ascension | |
| sun_dec | the sun's current declination | |
| sun_dist | the sun's distance from the current view point (to keep it inside your view volume.) | |
| moon_ra | the moon's current right ascension | |
| moon_dec | the moon's current declination | |
| moon_dist | the moon's distance from the current view point. |
| void SGSky::set_3dCloudDensity | ( | double | density | ) | [virtual] |
| void SGSky::set_3dCloudVisRange | ( | float | vis | ) | [virtual] |
| void SGSky::set_visibility | ( | float | v | ) | [inline] |
| void SGSky::texture_path | ( | const string & | path | ) |
1.6.1