345 lines
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HTML
345 lines
20 KiB
HTML
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<meta name="GENERATOR" content="Mozilla/4.77 [en] (X11; U; Linux 2.4.3-20mdk i686) [Netscape]">
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<title>Introduction to the OpenSceneGraph</title>
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<body bgcolor="#FFFFFF">
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<img SRC="images/OpenSceneGraphBanner_Distribution.jpg" BORDER=0>
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<table>
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<tr>
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<td><a href="index.html">Index</a></td>
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<td><a href="introduction.html">Introduction</a></td>
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<td><a href="contents.html">Contents</a></td>
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<td><a href="install.html">Install</a></td>
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<td><a href="dependencies.html">Dependencies</a></td>
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<td><a href="examples.html">examples</a></td>
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<td><a href="data.html">Data</a></td>
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<td><a href="osgviewer.html">Viewer</a></td>
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<td><a href="stereo.html">Stereo</a></td>
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<td><a href="plan.html">Plan</a></td>
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<td><a href="documentation.html">Reference Guides</a></td>
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</tr>
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</table>
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<h2>
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<u>Introduction to the OpenSceneGraph</u></h2>
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<p>The OpenSceneGraph is an portable, high level graphics toolkit for the development of high peformance
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graphics applications such as flight simulators, games, virtual reality or scientific visualization.
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Providing an object orientated framework on top of OpenGL, it frees the developer
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from implementing and optimizing low level graphics calls, and provide many additional utilities for
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rapid development of graphics applications.
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</p>
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<p>
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The project was started as a hobby by Don Burns in 1998, as means of porting a hang gliding simulator written on top of the
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Performer scene graph running on IRIX to what was then a humble Linux PC. In 1999, Robert Osfield began helping out with
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the simulator development and ported the scene graph element to Windows. In september 1999 the source code was open sourced,
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and the openscenegraph.org website was born, with Robert taking over as project lead and Don remaining focused on the hang
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gliding simulator.
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<p> In April 2001, in response to growing interest in the project around the world, Robert went fulltime
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on the project, setting up <a href="http://www.openscenegraph.com">OpenSceneGraph Professional Services</a> providing commericial support,
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consultancy services and training. At the end of 2001 Don also formed his own company <A HREF="http://www.andesengineering.com">Andes Computer Engineering</a>
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and participates in the development and support of OpenSceneGraph as well as complimentary projects like
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<A HREF="http://www.andesengineering.com/Producer">OpenProducer</A> and <A HREF="http://www.andesengineering.com/BlueMarbleViewer">BlueMarbleViewer</A>.
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<h3>
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<u>What is a Scene Graph?</u></h3>
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Its a tree! Quite simply one the best and most reusable data structures
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invented. Typically drawn schematically with the root at the top, leaves at the
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bottom. It all starts with a top-most root node which encompasses your whole
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virtual world, be it 2D or 3D. The world is then broken down into a hierarchy
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of nodes representing either spatial groupings of objects, settings of the
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position of objects, animations of objects, or definitions of logical relationships
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between objects such as those to manage the various states of a traffic light.
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The leaves of the graph represent the physical objects themselves, the
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drawable geometry and their material properties.
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</p>
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<p>A scene graph isn't a complete game or simulation engine, although it may
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be one of the main components of such an engine; it's primary focus is
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representation of your 3d worlds, and efficient rendering thereof. Physics models,
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collision detection and audio are left to other development libraries that
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a user will integrate with. The fact that scene graphs don't typically
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integrate all these features is actually a really good thing: it aids interoprability
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with clients' own applications and tools and allows it to serve many varied
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markets from games, visual simulation, virtual reality,
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scientific and commercial visualization, training through to modeling programs.
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</p>
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<h3>
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<u>Benefits that Scene Graphs provide</u></h3>
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The key reasons that many graphics developers uses scene graphs are <i>Performance, Productivity, Portability and Scalability:</i>
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<ul>
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<li><b><i>Performance</i></b></li>
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Scene graphs provide an excellent framework for
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maximizing graphics performance. A good scene graph employs two key techniques
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- culling of the objects that won't be seen on screen, and state sorting
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of properties such as textures and materials, so that all similar objects
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are drawn together. Without culling the CPU, buses and GPU will all become
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swamped by many times the amount of data than they actually require to
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represent your scenes accurately. The hierarchical structure of the scene
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graph makes this culling process very efficient, for instance a whole city can be culled
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with just a few operations! Without state sorting, the the buses and GPU
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will thrash between states, stalling the graphics pipeline and destroying graphics
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throughput. As GPU's get faster and faster, the cost of stalling the graphics pipeline
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is also going up, so scene graphs are becoming ever more important.
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<p>
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<li><b><i>Productivity</i></b></li>
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Scene graphs take away much of the hard work required
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to develop high performance graphics applications. The scene graph manages
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all the graphics for you, reducing what would be thousands of lines of
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OpenGL down to a few simple calls. Furthermore, one of most powerful concepts
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in Object Oriented programming is that of object composition, enshrined
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in the <i>Composite Design Pattern</i>, which fits the scene graph tree structure
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perfectly and makes it a highly flexible and reusable design - in real
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terms this means that it can be easily adapted to solve your problems.
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Scene graphs also often come additional utility libraries which range from
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helping users set up and manage graphics windows to importing of 3d models
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and images. All this together allows the user to achieve a great deal with
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very little coding. A dozen lines of code can be enough to load your data
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and create an interactive viewer!
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<p>
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<li><b><i>Portability</i></b></li>
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Scene graphs encapsulate much of the lower level
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tasks of rendering graphics and reading and writing data, reducing or even
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eradicating the platform specific coding that you require in your own application.
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If the underlying scene graph is portable then moving from platform to
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platform can be as simple as recompiling your source code.
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<p>
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<li><b><i>Scalability</i></b></li>
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Along with being able to dynamic manage the complexity
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of scenes automatically to account for differences in graphics performance
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across a range of machines, scene graphs also make it much easier to manage
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complex hardware configurations, such as clusters of graphics machines,
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or multiprocessor/multipipe systems such as SGI's Onyx. A good scene graph
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will allow the developer to concentrate on developing their own application
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while the rendering framework of the scene graph handles the different
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underlying hardware configurations.
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</ul>
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<h3>
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<u>The OpenSceneGraph - <i> a robust, high peformance Open Source scene graph</i></u></h3>
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With the OpenSceneGraph our goal is make the benefits of scene graph technology
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freely available to all, for both commericial and non commericial users. Whilst our scene graph
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is still in development, it has already gained a respect
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amongst the development community for its high performance, cleanness of
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design and portability. Written entirely in Standard C++ and OpenGL, it
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makes full use of the STL and Design Patterns, and leverages the open source
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development model to provide a development library that is legacy free
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and focused on the needs of end users. The OpenSceneGraph delivers on
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the four key benefits of scene graph technology outlined above with the
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following features:
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<ul>
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<li><b><i>Performance</i></b></li>
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Supports view frustum culling, occlusion culling, small feature culling,
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Level Of Detail (LOD) nodes, state sorting, vertex arrays and display
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lists as part of the core scene graph. These together make the OpenSceneGraph
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one of the highest performance scene graph available. User feedback is that
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performance matches or surpasses that of much more established scene graphs such
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as Performer, VTree, Vega Scene Graph and Java3D! The OpenSceneGraph also supports easy customization
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of the drawing process, which has allowed implementation of Continuous Level
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of Detail (CLOD) meshes on top the scene graph. These allow the visualization
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of massive terrain databases interactively, examples of this approach can
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be found at Vterrain.org and TerrainEngine.com, both of which integrate
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with the OpenSceneGraph.
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<p>
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<li><b><i>Productivity</i></b> </li>
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<p>
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The core scene graph provides encapsulate the majority of OpenGL
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functionality including latest extensions, provides rending optimizations
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such as culling and sorting, and a whole set of add on libraries which make
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it possible to develop high peformance graphics applications very rapidly. The
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application developer is freed to concentrate on content and how that content is
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controlled rather than low level coding.
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</p>
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<p>
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Combining lessons learned from established scene graphs like Performer
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and Open Inventor, with modern software engineering methods like Design Patterns,
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along with a great deal of feedback early on in the development cycle, it has been
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possible to design a library that is clean and extensible. This has made it easy
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for users to adopt to the OpenSceneGraph and to integrate it with their own applications.
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</p>
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<p>
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For reading and writing databases an the database library (osgDB) adds support for a wide
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variety of database formats via a extensible dynamic plugin mechansim - the distribution now includes 33
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seperate plugins for loading various 3D and Image data formats. 3D Database loaders include OpenFlight (.flt),
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TerraPage (.txp) including multi-threading support, LightWave (.lwo), Alias Wavefront (.obj),
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Carbon Graphics GEO (.geo), 3D Studio MAX (.3ds), Peformer (.pfb), Quake Character Models (.md2). Direct X (.x),
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and Inventor Ascii 2.0 (.iv)/ VRML 1.0 (.wrl), Designer Workshop (.dw) and AC3D (.ac) and the native .osg ASCII format.
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Image loaders include .rgb, .gif, .jpg, .png, .tiff, .pic, .bmp, .dds (include compressed mip mapped imagery), .tga and qucktime (under OSX).
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A whole set of high quality, anti-aliased fonts can also be loaded via the freetype plugin.
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</p>
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<p>
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The scene graph also has a set of <i>Node Kits</i> which are seperate libraries,
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that can be compiled in with your applications or loaded in at runtime, which add support for particle systems (osgParticle),
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high quality anti-aliased text (osgText) and navigational light points (osgSim).
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</p>
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<p>
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The community has also developed a number of additional <i>Node Kits</i> such as
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<a href="http://osgnv.sourceforge.net/">osgNV</a> (which includes support for NVidia's vertex, fragment, combiner etc extension and NVidia's Cg shader language.),
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<a href="http://www.terrainengine.com">Demeter</a> (CLOD terrain + integration with OSG).
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<a href="http://osgcal.sourceforge.net">osgCal</a> (which integrates <a href="http://cal3d.sourceforge.net//">Cal3D</a> and the OSG),
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<a href="http://www.cs.umu.se/kurser/TDBD12/HT02/lab/osgVortex/">osgVortex</a> (which integrates the <a href="http://www.cm-labs.com/">CM-Labs Vortex</a> physics enginer with OSG)
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and a whole set libraries that integrating the leading Windowing API's Links can be found in the bazaar sections on the
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<a href="http://www.openscenegraph.org/download/">download</a> page of OpenSceneGraph webiste.
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</p>
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<p>
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The project has also been integrated with <a href=http://www.vrjuggler.org/>VR Juggler</a> and
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<a href="http://http://vess.ist.ucf.edu/">Vess</a> virtual realilty the frameworks, with others in developments.
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<li><b><i>Portability</i></b></li>
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The core scene graph has also been designed to
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have minimal dependency on any specific platform, requiring little more than
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Standard C++ and OpenGL. This has allowed the scene graph to be rapidly
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ported to a wide range of platforms - originally developed on IRIX, then
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ported to Linux, then to Windows, then FreeBSD, Mac OSX, Solaris, HP-UX and
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we even a report of successful porting to PlayStation2!
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<br>
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The core scene graph library being completely windowing system independent makes
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it easy for users to add their own window-specific libraries and applications on top.
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In the distribution there is already the osgProducer library which integrates with <a href="http://www.andesengineering.com/Producer/">OpenProducer</a>, and in the Bazaar
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found at openscenegrph.org/download/ one can find examples of applications
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written on top of GLUT, Qt, MFC, WxWindows and SDL. Users have also integrated it
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with Motif, and X.
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<p>
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<li><b><i>Scalability</i></b></li>
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The scene graph will not only run on portables all
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the way up to Onyx Infinite Reality Monsters, but also supports the multiple
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graphics subsystems found on machines like a mulitpipe Onyx. This is
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possible because the core scene graph supports multiple graphics contexts
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for both OpenGL Display Lists and texture objects, and the cull and draw
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traversals have been designed to cache rendering data locally and use the
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scene graph almost entirely as a read-only operation. This allows multiple
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cull-draw pairs to run on multiple CPU's which are bound to multiple graphics
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subsystems. Support for multiple graphic context and multi-threading is all
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available out of the box via osgProducer - all the examples in the distribution
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can run multi-pipe just by use a simple configuation file.
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</ul>
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All the source to the OSG is published under the Open Scene Graph Public License
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(a relaxed version on the LGPL) which allows both open source and closed source projects to use,
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modify and distribute it freely as long its usage complies with the OSGPL.
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The project has been developed over the last four years, initiated by Don
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Burns, and then taken over by Robert Osfield who continues to lead the project
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today. There are many other contributors to the library, for a full list
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check out the AUTHORS file. Both Robert and Don now work on the OpenSceneGraph
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in a professional capacity providing consultancy and bespoke development
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on top the library, and are also collaborating on the book. Work on the
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core scene graph and support of public mailing list remains unpaid as are
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the contributions of the rest of the community, but this hasn't impacted
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the quality of the source or support which once you get stuck in you grow
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to appreciate.
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<p>The project is currently in beta, which means the main core features are now in
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place, with a 1.0 release in second half of 2003. Despite the beta development status,
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the project has already earned the reputation as the leading open source scene
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graph, and is establishing itself as a viable alternative to the commercial
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scene graphs. Numerous companies, university researchers and graphics enthusiasts
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have already adopted the OpenSceneGraph for their projects, all over the world.
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Examples of the wide variety of applications already developed ontop of the OpenSceneGraph include
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<a href="http://http://www.andesengineering.com/BlueMarbleViewer/">Blue Marble Viewer</a>,
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<a href="http://www.vterrain.org"> Virtual Terrain Project</a>,
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<a href="http://http://csp.sourceforge.net/">Combat Simulator Project</a>,
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<a href="http://osgedit.sourceforge.net/">OSG-Edit</a>. This is just a snippet of the projects
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that use the project, more examples can be found on the screenshot pages and bazaar on the website.
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</p>
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<h3>
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<u>Getting started</u></h3>
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The first thing is to select the distribution which suits you, there are
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binary, development and source code distributions, these can be loaded
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from the
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<a href="http://www.openscenegraph.org/download">http://www.openscenegraph.org/download</a>
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page. The latest developments area available as via a nightly tarball or
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via cvs.
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<p>The binary distribution contains just the libraries (.dll's /.so's)
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and example executables. This is suitable for using the OpenSceneGraph with
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an application that has already been compiled but depends at runtime on
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the OpenSceneGraph.
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</p>
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<p>The development distribution contains the libraries (.dll's /.so's),
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example executables, include files, and source to the examples. This is suitable
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for developers using the OpenSceneGraph.
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</p>
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<p>The source distribution contains all the source and include files
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required to build the OpenSceneGraph from scratch, and is ideal if you
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want to learn more about how the scene graph works, how to extend it, and
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to track down and fix any problems that you come across.
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</p>
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<p>If you are using a source distribution then read the <a href="install.html">installation</a>
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instructions for how to get the OpenSceneGraph compiling and installed
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on your system. You may also need to download libraries that parts of the
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OpenSceneGraph depend upon, such as Producer. Check the <a href="dependencies.html">dependencies</a>
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list for further details.
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</p>
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<p>For full instructions of how to run the examples read the <a href="examples.html">examples</a>
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page.
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</p>
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<h3>
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<u>Learning how to use the OpenSceneGraph</u></h3>
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<p>The OpenSceneGraph distribution comes with a reference guide for each of
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the component libraries - osg, osgDB, osgUtil, osgText, osgSim, osgParticle and osgProducer, a set
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of 42 examples - the source of which can be found in examples/ directory in the distribution. For questions
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or help which can't be easily be answered by the reference guide and examples
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source, one should join the mailing list (details below). There are also
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the beginnings of a <a href="http://www.c2.com/cgi/wiki?OpenSceneGraphFaq">Wiki
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based FAQ</a> which may help answer a few of the common queries.
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</p>
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<p>A programming guide will be available in form of a OpenSceneGraph book
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which is being written by Don Burns and Robert Osfield, parts of it will
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be available online.
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</p>
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<p>Although not directly related to the OpenSceneGraph, once can learn
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about scene graph technology from such sources as the <a href="http://www.sgi.com/software/inventor/manuals.html">Open
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Inventor Mentor</a>, and <a href="http://www.cineca.it/manuali/Performer/ProgGuide24/html">Performer
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Programming Guides</a>. The latter is the closer in design to
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the OpenSceneGraph, although the Performer manuals are in C, alas. Also of use
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as a background to some of the techniques used is a SIGGRAPH <a href="http://www.opengl.org/developers/code/sig99/advanced99/course_slides/vissim/index.htm">Vis-Sim
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course</a>.
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</p>
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<p>The OpenSceneGraph uses OpenGL and does so with a deliberately thin layer,
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making it easy to control the underlying OpenGL and to extend it with OpenGL
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extensions. The close tie with OpenGL is also reflected in the naming of
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many of the OpenGL state related classes, and the parameters that they
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encapsulate, which means that knowledge of OpenGL itself will go a long way
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to understanding how to get the best out of the OpenSceneGraph. To this
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end it is worth obtaining a copy of the OpenGL programming guide - <a href="http://fly.cc.fer.hr/~unreal/theredbook/">`Red
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Book`</a> and OpenGL reference guide 'Blue Book'. The main <a href="http://www.opengl.org">OpenGL
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website</a> is also a good source of links and further information.
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</p>
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<h3>
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<u>Support and discussion - the <i>openscenegraph-news</i> mailing list</u></h3>
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For scene graph related questions, bug reports, bug fixes, and general
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design and development discussion one should join the <a href="http://lists.sourceforge.net/mailman/listinfo/openscenegraph-news">openscenegraph-news</a>
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mailing list, and check the the mailing list <a href="http://sourceforge.net/mailarchive/forum.php?forum_id=4775">archives</a>.
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<p>Professional support is also available in the form of confidential online,
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phone and onsite support and consultancy, for details contact Robert Osfield
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at <a href="mailto:robert@openscenegraph.com">robert@openscenegraph.com</a>.
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</body>
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</html>
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