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OpenSG: A scene graph system for flexible and efficient realtime rendering for virtual and augmented reality applications

: Reiners, D.
: Encarnacao, J.L.; Müller, S.

Darmstadt, 2002
Darmstadt, TU, Diss., 2002
Fraunhofer IGD ()
scene graph; Realtime Rendering; virtual reality

This work covers the problems of scene graph systems. Currently used systems like Open Inventor or OpenGL Performer cover current and coming developments only partially. The work is concerned with three main parts: Extensibility, Parallelisation and Graphics Hardware Abstraction. Extensibility is a central problem given the quickly changing requirements posed by new applications. To support it new mechanisms are developed that allow dynamically extending the system. This concerns object creation as well as manipulation of objects, which is done via a reflectivity concept. The active components of the system, the traversals, have also been embedded into a new, extensible concept. Parallel processing is gaining importance due to the latest developments in processor and system architectures. In a VR application there are a number of independent tasks which can be executed in parallel and which access and anipulate the scene graph's data. To protect these from each other each task needs a private copy of the data. Using an appropriate synchronisation of accesses this division could be achieved using minimal memory overhead while allowing fast access and easy distribution of data between threads. Graphics hardware abstraction is forced by the growing diversification in the graphics board market. At the same time algorithms to create real time displays are moving further and further away from the classic, simple approaches and switch to using multiple stages and/or passes to create the final image. To give an application a usable access to these features without burdening it with too many details an extensible method to encapsulate the OpenGL state has mbeen developed, which together with a new structure called DrawTree is used optimize and abstract the display tasks. The central algorithms and methods developed in this work have been implemented in the free OpenSG system ( It is used and enhanced by a number of universities and research institutes.