/*! \page ogsflib GRASS GIS OGSF Library
<!-- doxygenized from "GRASS 5 Programmer's Manual"
     by M. Neteler 2/2004
     Updated by Martin Landa <landa.martin gmail.com> in 6/2011
  -->

by GRASS Development Team (https://grass.osgeo.org)

\section ogsfintro OGSF Library for OpenGL programming

<b>Overview</b>

The OGSF (gsurf) library, consisting of approximately 27,000 lines of
C code, contains some 250 public functions and about twice as many
internal functions for run-time data storage, manipulation, querying,
and visualization using OpenGL. The library handles all drawing and
lighting operations, including use of user-defined clipping planes and
drawing various style "fences" on clipping planes when drawing
multiple surfaces, and treats datasets as objects which can be used
for various attributes of the rendering.  It allows data sharing
(%e.g., same data for more than one attribute of same or different
surfaces), separate masking for each surface, multiple surfaces,
%vector sets, or %point sets, and will also allow multiple volumes.
The library provides all query features such as 3D "point on surface",
keyframe animation routines, and full state saving functionality.
Database-specific routines for interfacing with the \ref gislib are
kept isolated for easier library reuse with other databases.  The
gsurf library is not dependent upon any particular interface library,
and has been used successfully with both Motif, Tcl/Tk or wxPython. It
is used for Nviz visualization tool.

The library is designed to provide a unique "handle" or identifier
number to the calling program for each new geographic object added to
the model.  The object could be a surface, %vector set, or %point set,
which could each be defined by one or more database files. Once
created, the application only needs to keep track of the "handles" to
the objects (which are returned by the creation routines); for
example, to draw a surface the application would make the call:

\subsection ogsfNames Naming Conventions

The following naming conventions for function prefixes are used:

 - <b>GS_</b> - Functions which have to do with loading &amp;
        manipulating surfaces.  Also functions for library
        initialization, setting global variables, viewer positioning,
        and lighting.

 - <b>GSU_</b> - Utility functions for distance calculations, common
        2D &amp; 3D unit %vector operations such as cross product or
        %vector arithmetic.

 - <b>GV_</b> - Functions which have to do with loading &amp;
   manipulating %vector sets.

 - <b>GP_</b> - Functions which have to do with loading &amp;
   manipulating %point sets.

 - <b>GVL_</b> - Functions which have to do with loading &amp;
   manipulating 3D volumes.

 - <b>GK_</b> - Functions which have to do with setting &amp;
        manipulating keyframes for viewer position animation (fly-bys).

Programmers' documentation is currently incomplete, but see the
following for more details of the library design and capabilities in
the appendix (PLEASE ADD EXPLANATIONS!!):

 - public function prototypes
 - public include file include/gsurf.h
 - public include file include/keyframe.h
 - public color packing utility macros rgbpack.h
 - private types and defines include/gstypes.h
 - private utilities gsget.h

\section ogsfTodo Major todos

- remove global variables
- dynamically allocate items instead of static arrays
- merge GP_ functions into GV_

\section ogsfPublic Public function prototypes

\subsection ogsfGs Initialization and positioning surfaces (GS)

Functions which have to do with loading &amp; manipulating surfaces.
Also functions for library initialization, setting global variables,
viewer positioning, and lighting.

- GS_alldraw_cplane_fences()

- GS_alldraw_surf()

- GS_alldraw_wire()

- GS_check_cancel()

- GS_clear()

- GS_coordpair_repeats()

- GS_delete_list()

- GS_delete_surface()

- GS_distance()

- GS_done_draw()

- GS_draw_all_list()

- GS_draw_cplane()

- GS_draw_cplane_fence()

- GS_draw_flowline_at_xy()

- GS_draw_fringe()

- GS_draw_legend()

- GS_draw_lighting_model()

- GS_draw_lighting_model1()

- GS_draw_line_onsurf()

- GS_draw_nline_onsurf()

- GS_draw_surf()

- GS_draw_wire()

- GS_draw_X()

- GS_dv3norm()

- GS_geodistance()

- GS_get_aspect()

- GS_get_att()

- GS_get_cat_at_xy()

- GS_Get_ClientData()

- GS_get_dims()

- GS_get_distance_alongsurf()

- GS_get_drawmode()

- GS_get_drawres()

- GS_get_exag_guess()

- GS_get_fencecolor()

- GS_get_focus()

- GS_get_fov()

- GS_get_from()

- GS_get_from_real()

- GS_getlight_ambient()

- GS_getlight_color()

- GS_getlight_position()

- GS_get_longdim()

- GS_get_maskmode()

- GS_get_modelposition()

- GS_get_modelposition1()

- GS_get_norm_at_xy()

- GS_get_nozero()

- GS_get_region()

- GS_get_scale()

- GS_get_SDscale()

- GS_get_SDsurf()

- GS_get_selected_point_on_surface()

- GS_get_surf_list()

- GS_get_to()

- GS_get_to_real()

- GS_get_trans()

- GS_get_twist()

- GS_get_val_at_xy()

- GS_get_viewdir()

- GS_get_wire_color()

- GS_get_zextents()

- GS_get_zrange()

- GS_get_zrange_nz()

- GS_global_exag()

- GS_has_transparency()

- GS_init_view()

- GS_is_masked()

- GS_libinit()

- GS_lights_off()

- GS_lights_on()

- GS_load_3dview()

- GS_load_att_map()

- GS_look_here()

- GS_moveto()

- GS_moveto_real()

- GS_new_light()

- GS_new_surface()

- GS_num_surfs()

- GS_P2distance()

- GS_ready_draw()

- GS_save_3dview()

- GS_setall_drawmode()

- GS_setall_drawres()

- GS_set_att_const()

- GS_set_att_defaults()

- GS_set_cancel()

- GS_Set_ClientData()

- GS_set_cplane()

- GS_set_cplane_rot()

- GS_set_cplane_trans()

- GS_set_cxl_func()

- GS_set_draw()

- GS_set_drawmode()

- GS_set_drawres()

- GS_set_exag()

- GS_set_fencecolor()

- GS_set_focus()

- GS_set_focus_center_map()

- GS_set_focus_real()

- GS_set_fov()

- GS_set_global_exag()

- GS_set_infocus()

- GS_setlight_ambient()

- GS_setlight_color()

- GS_setlight_position()

- GS_set_maskmode()

- GS_set_Narrow()

- GS_set_nofocus()

- GS_set_nozero()

- GS_set_SDscale()

- GS_set_SDsurf()

- GS_set_trans()

- GS_set_twist()

- GS_set_viewdir()

- GS_set_viewport()

- GS_set_wire_color()

- GS_surf_exists()

- GS_switchlight()

- GS_transp_is_set()

- GS_unset_att()

- GS_unset_cplane()

- GS_unset_SDsurf()

- GS_update_curmask()

- GS_update_normals()

- GS_util.c()

- GS_v2dir()

- GS_v2norm()

- GS_v3add()

- GS_v3cross()

- GS_v3dir()

- GS_v3eq()

- GS_v3mag()

- GS_v3mult()

- GS_v3norm()

- GS_v3normalize()

- GS_v3sub()

- GS_write_ppm()

- GS_write_tif()

- GS_write_zoom()

- GS_zoom_setup()

\subsection ogsfGv Loading and manipulation of vector maps (GV)

Functions which have to do with loading &amp; manipulating %vector
sets.

- GV_alldraw_fastvect()

- GV_alldraw_vect()

- GV_delete_vector()

- GV_draw_fastvect()

- GV_draw_vect()

- GV_Get_ClientData()

- GV_get_trans()

- GV_get_vect_list()

- GV_get_style()

- GV_get_vectname()

- GV_load_vector()

- GV_new_vector()

- GV_num_vects()

- GV_select_surf()

- GV_Set_ClientData()

- GV_set_trans()

- GV_set_style()

- GV_surf_is_selected()

- GV_unselect_surf()

- GV_vect_exists()

\subsection ogsfGp Loading and manipulation of vector point maps (GP)

Functions which have to do with loading &amp; manipulating %point
sets.

- GP_alldraw_site()

- GP_attmode_color()

- GP_attmode_none()

- GP_delete_site()

- GP_draw_site()

- GP_Get_ClientData()

- GP_get_site_list()

- GP_get_sitename()

- GP_get_style()

- GP_get_trans()

- GP_get_zmode()

- GP_load_site()

- GP_new_site()

- GP_num_sites()

- GP_select_surf()

- GP_Set_ClientData()

- GP_set_style()

- GP_set_style_thematic()

- GP_set_trans()

- GP_set_zmode()

- GP_site_exists()

- GP_str_to_marker()

- GP_surf_is_selected()

- GP_unselect_surf()

\subsection ogsf ogsfGk Keyframe animation

Functions which have to do with setting &amp; manipulating keyframes
for viewer position animation (fly-bys).

- GK_add_key()

- GK_clear_keys()

- GK_delete_key()

- GK_do_framestep()

- GK_move_key()

- GK_print_keys()

- GK_set_interpmode()

- GK_set_numsteps()

- GK_set_tension()

- GK_show_list()

- GK_show_path()

- GK_show_site()

- GK_showtension_start()

- GK_showtension_stop()

- GK_show_vect()

- GK_show_vol()

- GK_update_frames()

- GK_update_tension()


\subsection ogsfGvl  Loading and manipulation of volume maps (GVL)

Functions which have to do with loading &amp; manipulating 3D volumes.

- GVL_alldraw_vol()

- GVL_alldraw_wire()

- GVL_delete_vol()

- GVL_draw_vol()

- GVL_draw_wire()

- GVL_Get_ClientData()

- GVL_get_dims()

- GVL_get_region()

- GVL_get_trans()

- GVL_get_vol_list()

- GVL_get_volname()

- GVL_get_window()

- GVL_isosurf_add()

- GVL_isosurf_del()

- GVL_isosurf_get_att()

- GVL_isosurf_get_drawmode()

- GVL_isosurf_get_drawres()

- GVL_isosurf_get_flags()

- GVL_isosurf_get_maskmode()

- GVL_isosurf_move_down()

- GVL_isosurf_move_up()

- GVL_isosurf_num_isosurfs()

- GVL_isosurf_set_att_const()

- GVL_isosurf_set_att_map()

- GVL_isosurf_set_drawmode()

- GVL_isosurf_set_drawres()

- GVL_isosurf_set_flags()

- GVL_isosurf_set_maskmode()

- GVL_isosurf_unset_att()

- GVL_libinit()

- GVL_load_vol()

- GVL_new_vol()

- GVL_num_vols()

- GVL_Set_ClientData()

- GVL_set_focus_center_map()

- GVL_set_trans()

- GVL_slice_add()

- GVL_slice_del()

- GVL_slice_get_drawmode()

- GVL_slice_get_drawres()

- GVL_slice_get_pos()

- GVL_slice_get_transp()

- GVL_slice_move_down()

- GVL_slice_move_up()

- GVL_slice_num_slices()

- GVL_slice_set_drawmode()

- GVL_slice_set_drawres()

- GVL_slice_set_pos()

- GVL_slice_set_transp()

- GVL_vol_exists()

\subsection ogsfGvlIso Loading and manipulation of isosurfaces (GVL)

Functions which have to do with loading &amp; manipulating
isosurfaces.

- GVL_isosurf_add()

- GVL_isosurf_del()

- GVL_isosurf_get_att()

- GVL_isosurf_get_drawmode()

- GVL_isosurf_get_drawres()

- GVL_isosurf_get_flags()

- GVL_isosurf_get_maskmode()

- GVL_isosurf_move_down()

- GVL_isosurf_move_up()

- GVL_isosurf_num_isosurfs()

- GVL_isosurf_set_att_const()

- GVL_isosurf_set_att_map()

- GVL_isosurf_set_drawmode()

- GVL_isosurf_set_drawres()

- GVL_isosurf_set_flags()

- GVL_isosurf_set_maskmode()

- GVL_isosurf_unset_att()

\subsection ogsfGvlSlice  Loading and manipulation of slices (GVL)

Functions which have to do with loading &amp; manipulating slices.

- GVL_slice_add()

- GVL_slice_del()

- GVL_slice_get_drawmode()

- GVL_slice_get_drawres()

- GVL_slice_get_pos()

- GVL_slice_get_transp()

- GVL_slice_move_down()

- GVL_slice_move_up()

- GVL_slice_num_slices()

- GVL_slice_set_drawmode()

- GVL_slice_set_drawres()

- GVL_slice_set_pos()

- GVL_slice_set_transp()

\section authors Authors

 Bill Brown GMSL/University of Illinois

*/