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flightgear/src/Scenery/scenery.hxx
ehofman 4c10ef139c Mathias:
I have done a patch to eliminate the jitter of 3D-objects near the viewpoint
(for example 3D cockpit objects).
The problem is the roundoff accuracy of the float values used in the
scenegraph together with the transforms of the eyepoint relative to the
scenery center.

The solution will be to move the scenery center near the view point.
This way floats relative accuracy is enough to show a stable picture.

To get that right I have introduced a transform node for the scenegraph which
is responsible for that shift and uses double values as long as possible.
The scenery subsystem now has a list of all those transforms required to place
objects in the world and will tell all those transforms that the scenery
center has changed when the set_scenery_center() of the scenery subsystem is
called.
The problem was not solvable by SGModelPlacement and SGLocation, since not all
objects, especially the scenery, are placed using these classes.

The first approach was to have the scenery center exactly at the eyepoint.
This works well for the cockpit.
But then the ground jitters a bit below the aircraft. With our default views
you can't see that, but that F-18 has a camera view below the left engine
intake with the nose gear and the ground in its field of view, here I could
see that.
Having the scenery center constant will still have this roundoff problems, but
like it is now too, the roundoff error here is exactly the same in each
frame, so you will not notice any jitter.

The real solution is now to keep the scenery center constant as long as it is
in a ball of 30m radius around the view point. If the scenery center is
outside this ball, just put it at the view point.

As a sideeffect of now beeing able to switch the scenery center in the whole
scenegraph with one function call, I was able to remove a one half of a
problem when switching views, where the scenery center was far off for one or
two frames past switching from one view to the next. Also included is a fix
to the other half of this problem, where the view position was not yet copied
into a view when it is switched (at least under glut). This was responsible
for the 'Error: ...' messages of the cloud subsystem when views were
switched.
2005-04-29 14:38:24 +00:00

161 lines
4.5 KiB
C++

// scenery.hxx -- data structures and routines for managing scenery.
//
// Written by Curtis Olson, started May 1997.
//
// Copyright (C) 1997 Curtis L. Olson - http://www.flightgear.org/~curt
//
// 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 _SCENERY_HXX
#define _SCENERY_HXX
#ifndef __cplusplus
# error This library requires C++
#endif
#include <list>
#include <plib/sg.h>
#include <simgear/compiler.h>
#include <simgear/structure/subsystem_mgr.hxx>
#include <simgear/math/point3d.hxx>
SG_USING_STD(list);
class ssgRoot;
class ssgBranch;
class ssgPlacementTransform;
// Define a structure containing global scenery parameters
class FGScenery : public SGSubsystem {
// center of current scenery chunk
Point3D center;
// next center of current scenery chunk
Point3D next_center;
// angle of sun relative to current local horizontal
double sun_angle;
// elevation of terrain at our current lat/lon (based on the
// actual drawn polygons)
double cur_elev;
// the distance (radius) from the center of the earth to the
// current scenery elevation point
double cur_radius;
// unit normal at point used to determine current elevation
sgdVec3 cur_normal;
// SSG scene graph
ssgRoot *scene_graph;
ssgBranch *terrain_branch;
ssgRoot *gnd_lights_root;
ssgRoot *vasi_lights_root;
ssgRoot *rwy_lights_root;
ssgRoot *taxi_lights_root;
ssgBranch *models_branch;
ssgBranch *aircraft_branch;
// list of all placement transform, used to move the scenery center on the fly.
typedef list<ssgPlacementTransform*> placement_list_type;
placement_list_type _placement_list;
public:
FGScenery();
~FGScenery();
// Implementation of SGSubsystem.
void init ();
void bind ();
void unbind ();
void update (double dt);
inline double get_cur_elev() const { return cur_elev; }
inline void set_cur_elev( double e ) { cur_elev = e; }
inline Point3D get_center() const { return center; }
void set_center( Point3D p );
inline Point3D get_next_center() const { return next_center; }
inline void set_next_center( Point3D p ) { next_center = p; }
inline void set_cur_radius( double r ) { cur_radius = r; }
inline void set_cur_normal( sgdVec3 n ) { sgdCopyVec3( cur_normal, n ); }
inline ssgRoot *get_scene_graph () const { return scene_graph; }
inline void set_scene_graph (ssgRoot * s) { scene_graph = s; }
inline ssgBranch *get_terrain_branch () const { return terrain_branch; }
inline void set_terrain_branch (ssgBranch * t) { terrain_branch = t; }
inline ssgRoot *get_gnd_lights_root () const {
return gnd_lights_root;
}
inline void set_gnd_lights_root (ssgRoot *r) {
gnd_lights_root = r;
}
inline ssgRoot *get_vasi_lights_root () const {
return vasi_lights_root;
}
inline void set_vasi_lights_root (ssgRoot *r) {
vasi_lights_root = r;
}
inline ssgRoot *get_rwy_lights_root () const {
return rwy_lights_root;
}
inline void set_rwy_lights_root (ssgRoot *r) {
rwy_lights_root = r;
}
inline ssgRoot *get_taxi_lights_root () const {
return taxi_lights_root;
}
inline void set_taxi_lights_root (ssgRoot *r) {
taxi_lights_root = r;
}
inline ssgBranch *get_models_branch () const {
return models_branch;
}
inline void set_models_branch (ssgBranch *t) {
models_branch = t;
}
inline ssgBranch *get_aircraft_branch () const {
return aircraft_branch;
}
inline void set_aircraft_branch (ssgBranch *t) {
aircraft_branch = t;
}
void register_placement_transform(ssgPlacementTransform *trans);
void unregister_placement_transform(ssgPlacementTransform *trans);
};
#endif // _SCENERY_HXX