OpenSceneGraph/include/osgSim/Impostor
2012-03-21 17:36:20 +00:00

122 lines
4.8 KiB
C++

/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 Robert Osfield
*
* This library is open source and may be redistributed and/or modified under
* the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or
* (at your option) any later version. The full license is in LICENSE file
* included with this distribution, and on the openscenegraph.org website.
*
* This library 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
* OpenSceneGraph Public License for more details.
*/
#ifndef OSGSIM_IMPOSTOR
#define OSGSIM_IMPOSTOR 1
#include <osg/LOD>
#include <osg/buffered_value>
#include <osgUtil/CullVisitor>
#include <osgSim/ImpostorSprite>
namespace osgSim {
/** Impostor - is a form of Level Of Detail group node which allows both switching
* between children depending on distance from eye point and image caching.
*
* The principle behind Imposters is that they cache an image of real geometry and then the image is drawn
* in subsequent frames instead of the real geometry. It's a bit like a
* Billboard *but* is updated at runtime and w.r.t view point. By drawing
* just the texture mapped quad you can cut down scene complexity and
* improve performance.
*
* For more details have a look at:
*
* http://grail.cs.washington.edu/projects/hic/
*
* The OSG doesn't implement exactly the same technique as above, but its
* should be a good starting place. The OSG's impostors are much less
* intrusive since you don't need to restructure your whole scene to use
* them.
*
* All you need to do to use Impostors is to set up the visible
* range values for each LOD child of the Impostor, as per osg::LOD,
* and set an Impostor threshold to tell the renderer at what distance
* the Impostor's image caching should cut in. The osg::CullVisitor
* automatically handles all the setting of pre-rendering stages to
* calculate the required ImpostorSprites (which encapsulates the image
* cache and quad), and updates them as the view point changes. If you
* use osg::SceneView/CullVisitor all the complexity of supporting
* Impostor will be nicely hidden away.
*
* TODO:
* Various improvements are planned for the Impostor-
* 1) Estimation of how many frames an ImpostorSprite will be reused, if
* it won't be used more often than a minimum threshold then do not create
* ImpostorSprite - use the real geometry.
* 2) Sharing of texture memory between ImpostorSprites.
* 3) Simple 3D geometry for ImpostorSprite's rather than Billboarding.
* 4) Shrinking of the ImpostorSprite size to more closely fit the underlying
* geometry.
*/
class OSGSIM_EXPORT Impostor : public osg::LOD
{
public :
Impostor();
Impostor(const Impostor& es, const osg::CopyOp& copyop=osg::CopyOp::SHALLOW_COPY):
osg::LOD(es,copyop),
_impostorThreshold(es._impostorThreshold) {}
META_Node(osgSim, Impostor);
virtual void traverse(osg::NodeVisitor& nv);
typedef std::vector< osg::ref_ptr<ImpostorSprite> > ImpostorSpriteList;
/** Set the Impostor threshold distance.
* For eye points further than this threshold the Imposter is used if appropriate,
* otherwise the LOD children as chosen as per a standard LOD node.
*/
inline void setImpostorThreshold(float distance) { _impostorThreshold = distance; }
/* Get the Impostor threshold distance. */
inline float getImpostorThreshold() const { return _impostorThreshold; }
/** Set the Impostor threshold distance relative to the node's bounding
* sphere's radius.
*/
inline void setImpostorThresholdToBound(float ratio=1.0f) { _impostorThreshold = getBound().radius()*ratio; }
/** Find the ImposterSprite which fits the current eye point best. */
ImpostorSprite* findBestImpostorSprite(unsigned int contextID, const osg::Vec3& currLocalEyePoint) const;
/** Add an ImpostorSprite to the Impostor. */
void addImpostorSprite(unsigned int contextID, ImpostorSprite* is);
/** Get the list of ImpostorSprites attached to this Impostor. */
inline ImpostorSpriteList& getImpostorSpriteList(unsigned int contexID) { return _impostorSpriteListBuffer[contexID]; }
/** Get a const list of ImpostorSprites attached to this const Impostor. */
inline const ImpostorSpriteList& getImpostorSpriteList(unsigned int contexID) const { return _impostorSpriteListBuffer[contexID]; }
virtual osg::BoundingSphere computeBound() const;
protected :
virtual ~Impostor() {}
mutable osg::buffered_object<ImpostorSpriteList> _impostorSpriteListBuffer;
ImpostorSprite* createImpostorSprite(osgUtil::CullVisitor* cv);
float _impostorThreshold;
};
}
#endif