98 lines
3.8 KiB
Plaintext
98 lines
3.8 KiB
Plaintext
#ifndef OSG_IMPOSTOR
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#define OSG_IMPOSTOR 1
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#include <osg/LOD>
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#include <osg/ImpostorSprite>
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namespace osg {
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/** Impostor - is a form of Level Of Detail group node which allows both switching
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* between children depending on distance from eye point and image caching.
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*
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* The principle behind Imposters is that they cache an image of real geometry and then the image is drawn
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* in subsequent frames instead of the real geometry. Its a bit like a
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* Billboard *but* is updated at runtime and w.r.t view point. By drawing
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* just the texture mapped quad you can cut down scene complexity and
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* improve performance.
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*
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* For more details have a look at:
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*
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* http://grail.cs.washington.edu/projects/hic/
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*
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* The OSG doesn't implement exactly the same technique as above, but its
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* should be a good starting place. The OSG's impostors are much less
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* intrusive since you don't need to restructure your whole scene to use
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* them.
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*
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* All you need to do to use Impostors is to set up the visible
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* range values for each LOD child of the Impostor, as per osg::LOD,
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* and set an Impostor threshold to tell the renderer at what distance
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* the Impostor's image caching should cut in. The osg::CullVisitor
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* automatically handles all the setting of pre-rendering stages to
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* calculate the required ImpostorSprites (which encapsulates the image
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* cache and quad), and updates them as the view point changes. If you
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* use osg::SceneView/CullVisitor all the complexity of supporting
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* Impostor will be nicely hidden away.
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*
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* TODO:
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* Various improvements are planned for the Impostor-
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* 1) Estimation of how many frames an ImpostorSprite will be reused, if
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* it won't be used more often than a minimum threshold then do not create
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* ImpostorSprite - use the real geometry.
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* 2) Sharing of texture memory between ImpostorSprites.
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* 3) Simple 3D geometry for ImpostorSprite's rather than Billboarding.
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* 4) Shrinking of the ImpostorSprite size to more closely fit the underlying
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* geometry.
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*/
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class SG_EXPORT Impostor : public LOD
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{
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public :
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Impostor();
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META_Node(Impostor);
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typedef std::vector< ref_ptr<ImpostorSprite> > ImpostorSpriteList;
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/** Set the Impostor threshold distance.
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* For eye points further than this threshold the Imposter is used if appropriate,
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* otherwise the LOD children as chosen as per a standard LOD node.*/
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inline void setImpostorThreshold(float distance) { _impostorThreshold = distance; }
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/** Set the Impostor threshold distance relative to the node's bounding
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* sphere's radius.*/
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inline void setImpostorThresholdToBound(float ratio=1.0f) { _impostorThreshold = getBound().radius()*ratio; }
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/* Get the Impostor threshold distance.*/
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inline const float getImpostorThreshold() const { return _impostorThreshold; }
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/* Get the Impostor threshold distance squared.*/
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inline const float getImpostorThreshold2() const { return _impostorThreshold*_impostorThreshold; }
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/** Find the ImposterSprite which fits the current eye point best.*/
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ImpostorSprite* findBestImpostorSprite(const osg::Vec3& currLocalEyePoint);
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/** Add an ImpostorSprite to the Impostor.*/
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void addImpostorSprite(ImpostorSprite* is);
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/** Get the list of ImpostorSprites attached to this Impostor.*/
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inline ImpostorSpriteList& getImpostorSpriteList() { return _impostorSpriteList; }
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/** Get a const list of ImpostorSprites attached to this const Impostor.*/
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inline const ImpostorSpriteList& getImpostorSpriteList() const { return _impostorSpriteList; }
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protected :
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virtual ~Impostor() {}
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virtual const bool computeBound() const;
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ImpostorSpriteList _impostorSpriteList;
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float _impostorThreshold;
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};
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};
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#endif
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