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1/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 Robert Osfield
2 *
3 * This library is open source and may be redistributed and/or modified under
4 * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or
5 * (at your option) any later version.  The full license is in LICENSE file
6 * included with this distribution, and on the openscenegraph.org website.
7 *
8 * This library is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
11 * OpenSceneGraph Public License for more details.
12*/
13
14#ifndef OSGSIM_IMPOSTOR
15#define OSGSIM_IMPOSTOR 1
16
17#include <osg/LOD>
18#include <osg/buffered_value>
19
20#include <osgUtil/CullVisitor>
21
22#include <osgSim/ImpostorSprite>
23
24namespace osgSim {
25
26/** Impostor - is a form of Level Of Detail group node which allows both switching
27  * between children depending on distance from eye point and image caching.
28  *
29  * The principle behind Imposters is that they cache an image of real geometry and then the image is drawn
30  * in subsequent frames instead of the real geometry. It's a bit like a
31  * Billboard *but* is updated at runtime and w.r.t view point. By drawing
32  * just the texture mapped quad you can cut down scene complexity and
33  * improve performance.
34  *
35  * For more details have a look at:
36  *
37  *    http://grail.cs.washington.edu/projects/hic/
38  *
39  * The OSG doesn't implement exactly the same technique as above, but its
40  * should be a good starting place. The OSG's impostors are much less
41  * intrusive since you don't need to restructure your whole scene to use
42  * them.
43  *
44  * All you need to do to use Impostors is to set up the visible
45  * range values for each LOD child of the Impostor, as per osg::LOD,
46  * and set an Impostor threshold to tell the renderer at what distance
47  * the Impostor's image caching should cut in.  The osg::CullVisitor
48  * automatically handles all the setting of pre-rendering stages to
49  * calculate the required ImpostorSprites (which encapsulates the image
50  * cache and quad), and updates them as the view point changes. If you
51  * use osg::SceneView/CullVisitor all the complexity of supporting
52  * Impostor will be nicely hidden away.
53  *
54  * TODO:
55  * Various improvements are planned for the Impostor-
56  * 1) Estimation of how many frames an ImpostorSprite will be reused, if
57  * it won't be used more often than a minimum threshold then do not create
58  * ImpostorSprite - use the real geometry.
59  * 2) Sharing of texture memory between ImpostorSprites.
60  * 3) Simple 3D geometry for ImpostorSprite's rather than Billboarding.
61  * 4) Shrinking of the ImpostorSprite size to more closely fit the underlying
62  * geometry.
63  */
64class OSGSIM_EXPORT Impostor : public osg::LOD
65{
66    public :
67        Impostor();
68
69        Impostor(const Impostor& es, const osg::CopyOp& copyop=osg::CopyOp::SHALLOW_COPY):
70            osg::LOD(es,copyop),
71            _impostorThreshold(es._impostorThreshold) {}
72
73        META_Node(osgSim, Impostor);
74
75        virtual void traverse(osg::NodeVisitor& nv);
76
77        typedef std::vector< osg::ref_ptr<ImpostorSprite> > ImpostorSpriteList;
78
79        /** Set the Impostor threshold distance.
80          * For eye points further than this threshold the Imposter is used if appropriate,
81          * otherwise the LOD children as chosen as per a standard LOD node.
82        */
83        inline void setImpostorThreshold(float distance) { _impostorThreshold = distance; }
84
85        /* Get the Impostor threshold distance. */
86        inline float getImpostorThreshold() const { return _impostorThreshold; }
87
88        /** Set the Impostor threshold distance relative to the node's bounding
89          * sphere's radius.
90          */
91        inline void setImpostorThresholdToBound(float ratio=1.0f) { _impostorThreshold = getBound().radius()*ratio; }
92
93        /** Find the ImposterSprite which fits the current eye point best. */
94        ImpostorSprite* findBestImpostorSprite(unsigned int contextID, const osg::Vec3& currLocalEyePoint) const;
95
96        /** Add an ImpostorSprite to the Impostor. */
97        void addImpostorSprite(unsigned int contextID, ImpostorSprite* is);
98
99        /** Get the list of ImpostorSprites attached to this Impostor. */
100        inline ImpostorSpriteList& getImpostorSpriteList(unsigned int contexID) { return _impostorSpriteListBuffer[contexID]; }
101
102        /** Get a const list of ImpostorSprites attached to this const Impostor. */
103        inline const ImpostorSpriteList& getImpostorSpriteList(unsigned int contexID) const { return _impostorSpriteListBuffer[contexID]; }
104
105        virtual osg::BoundingSphere computeBound() const;
106
107    protected :
108
109        virtual ~Impostor() {}
110
111        mutable osg::buffered_object<ImpostorSpriteList>  _impostorSpriteListBuffer;
112
113        ImpostorSprite* createImpostorSprite(osgUtil::CullVisitor* cv);
114
115        float _impostorThreshold;
116
117};
118
119}
120
121#endif
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