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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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</head>
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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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<tbody>
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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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</tbody>
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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
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the development of high peformance
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graphics applications such as flight simulators, games, virtual reality
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or scientific visualization. Providing an object orientated framework
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on top of OpenGL, it frees the developer
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from implementing and optimizing low level graphics calls, and provide
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many additional utilities for rapid development of graphics
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applications. </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
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porting a hang gliding simulator written on top of the Performer scene
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graph running on IRIX to what was then a humble Linux PC. In 1999,
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Robert Osfield began helping out with the simulator development and
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ported the scene graph element to Windows. In september 1999 the source
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code was open sourced, and the openscenegraph.org website was born,
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with Robert taking over as project lead and Don remaining focused on
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the hang gliding simulator.
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</p>
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<p> In April 2001, in response to growing interest in the project
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around the world, Robert went fulltime on the project, setting up <a
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href="http://www.openscenegraph.com">OpenSceneGraph Professional
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Services</a> providing commericial support, consultancy services and
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training. At the end of 2001 Don also formed his own company <a
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href="http://www.andesengineering.com">Andes Computer Engineering</a>
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and participates in the development and support of OpenSceneGraph as
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well as complimentary projects like <a
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href="http://www.andesengineering.com/Producer">OpenProducer</a> and <a
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href="http://www.andesengineering.com/BlueMarbleViewer">BlueMarbleViewer</a>.
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</p>
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<h3><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,
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leaves at the
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bottom. It all starts with a top-most root node which encompasses your
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whole
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virtual world, be it 2D or 3D. The world is then broken down into a
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hierarchy
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of nodes representing either spatial groupings of objects, settings of
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the
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position of objects, animations of objects, or definitions of logical
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relationships
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between objects such as those to manage the various states of a traffic
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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></p>
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<p>A scene graph isn't a complete game or simulation engine, although
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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.
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Physics models,
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collision detection and audio are left to other development libraries
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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
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interoprability
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with clients' own applications and tools and allows it to serve many
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varied
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markets from games, visual simulation, virtual reality,
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scientific and commercial visualization, training through to modeling
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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,
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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
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techniques
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- culling of the objects that won't be seen on screen, and state
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sorting
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of properties such as textures and materials, so that all similar
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objects
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are drawn together. Without culling the CPU, buses and GPU will all
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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
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scene
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graph makes this culling process very efficient, for instance a whole
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city can be culled
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with just a few operations! Without state sorting, the the buses and
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GPU
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will thrash between states, stalling the graphics pipeline and
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destroying graphics
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throughput. As GPU's get faster and faster, the cost of stalling the
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graphics pipeline
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is also going up, so scene graphs are becoming ever more important.
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<p></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
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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
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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
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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
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from
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helping users set up and manage graphics windows to importing of 3d
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models
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and images. All this together allows the user to achieve a great deal
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with
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very little coding. A dozen lines of code can be enough to load your
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data
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and create an interactive viewer!
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<p></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
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even
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eradicating the platform specific coding that you require in your own
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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></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
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performance
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across a range of machines, scene graphs also make it much easier to
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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
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graph
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will allow the developer to concentrate on developing their own
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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
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scene graph</i></u></h3>
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With the OpenSceneGraph our goal is make the benefits of scene graph
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technology freely available to all, for both commericial and non
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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
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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
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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
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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
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OpenSceneGraph
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one of the highest performance scene graph available. User feedback is
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that
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performance matches or surpasses that of much more established scene
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graphs such as Performer, VTree, Vega Scene Graph and Java3D! The
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OpenSceneGraph also supports easy customization
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of the drawing process, which has allowed implementation of Continuous
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Level
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of Detail (CLOD) meshes on top the scene graph. These allow the
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visualization
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of massive terrain databases interactively, examples of this approach
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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></p>
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<li><b><i>Productivity</i></b> </li>
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<p>The core scene graph provides encapsulate the majority of OpenGL
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functionality including latest extensions, provides rending
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optimizations
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such as culling and sorting, and a whole set of add on libraries which
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make
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it possible to develop high peformance graphics applications very
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rapidly. The application developer is freed to concentrate on content
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and how that content is controlled rather than low level coding. </p>
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<p>Combining lessons learned from established scene graphs like
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Performer
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and Open Inventor, with modern software engineering methods like Design
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Patterns, along with a great deal of feedback early on in the
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development cycle, it has been possible to design a library that is
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clean and extensible. This has made it easy for users to adopt to the
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OpenSceneGraph and to integrate it with their own applications. </p>
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<p>For reading and writing databases an the database library (osgDB)
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adds
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support for a wide
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variety of database formats via a extensible dynamic plugin mechansim -
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the distribution now includes 33
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seperate plugins for loading various 3D and Image data formats. 3D
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Database loaders include OpenFlight (.flt), TerraPage (.txp) including
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multi-threading support, LightWave (.lwo), Alias Wavefront (.obj),
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Carbon Graphics GEO (.geo), 3D Studio MAX (.3ds), Peformer (.pfb),
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Quake Character Models (.md2). Direct X (.x), and Inventor Ascii 2.0
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(.iv)/ VRML 1.0 (.wrl), Designer Workshop (.dw) and AC3D (.ac) and the
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native .osg ASCII format.
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Image loaders include .rgb, .gif, .jpg, .png, .tiff, .pic, .bmp, .dds
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(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
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the freetype plugin. </p>
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<p>The scene graph also has a set of <i>Node Kits</i> which are
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seperate
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libraries,
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that can be compiled in with your applications or loaded in at runtime,
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which add support for particle systems (osgParticle),
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high quality anti-aliased text (osgText) and navigational light points
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(osgSim). </p>
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<p>The community has also developed a number of additional <i>Node
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Kits</i>
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such as <a href="http://osgnv.sourceforge.net/">osgNV</a> (which
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includes support for NVidia's vertex, fragment, combiner etc extension
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and NVidia's Cg shader language.), <a
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href="http://www.terrainengine.com">Demeter</a> (CLOD terrain +
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integration with OSG). <a href="http://osgcal.sourceforge.net">osgCal</a>
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(which integrates <a href="http://cal3d.sourceforge.net//">Cal3D</a>
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and the OSG), <a href="http://www.vrlab.umu.se/research/osgvortex">osgVortex</a>
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(which integrates the <a href="http://www.cm-labs.com/">CM-Labs Vortex</a>
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physics enginer with OSG)
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and a whole set libraries that integrating the leading Windowing API's
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Links can be found in the bazaar sections on the <a
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href="http://www.openscenegraph.org/download/">download</a> page of
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OpenSceneGraph webiste. </p>
|
2003-12-04 05:45:32 +08:00
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<p>The project has also been integrated with <a
|
2003-11-25 17:23:04 +08:00
|
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href="http://www.vrjuggler.org/">VR Juggler</a> and <a
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href="http://http://vess.ist.ucf.edu/">Vess</a> virtual realilty the
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frameworks, with others in developments. </p>
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|
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<li><b><i>Portability</i></b></li>
|
2003-04-25 03:54:03 +08:00
|
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The core scene graph has also been designed to
|
2003-11-25 17:23:04 +08:00
|
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have minimal dependency on any specific platform, requiring little more
|
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|
than
|
2002-05-22 03:34:16 +08:00
|
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|
Standard C++ and OpenGL. This has allowed the scene graph to be rapidly
|
2003-11-25 17:23:04 +08:00
|
|
|
ported to a wide range of platforms - originally developed on IRIX,
|
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|
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then
|
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|
ported to Linux, then to Windows, then FreeBSD, Mac OSX, Solaris, HP-UX
|
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|
and we even a report of successful porting to PlayStation2! <br>
|
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|
The core scene graph library being completely windowing system
|
|
|
|
|
independent makes it easy for users to add their own window-specific
|
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|
|
|
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>,
|
|
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|
|
and in the Bazaar
|
|
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|
found at openscenegrph.org/download/ one can find examples of
|
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|
|
applications
|
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|
written on top of GLUT, Qt, MFC, WxWindows and SDL. Users have also
|
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|
integrated it
|
2002-04-25 14:27:09 +08:00
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with Motif, and X.
|
2003-11-25 17:23:04 +08:00
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<p></p>
|
|
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|
|
<li><b><i>Scalability</i></b></li>
|
2003-04-25 03:54:03 +08:00
|
|
|
The scene graph will not only run on portables all
|
2003-11-25 17:23:04 +08:00
|
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|
the way up to Onyx Infinite Reality Monsters, but also supports the
|
|
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|
|
multiple
|
2002-05-22 03:34:16 +08:00
|
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|
graphics subsystems found on machines like a mulitpipe Onyx. This is
|
2003-11-25 17:23:04 +08:00
|
|
|
possible because the core scene graph supports multiple graphics
|
|
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|
|
contexts
|
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|
|
for both OpenGL Display Lists and texture objects, and the cull and
|
|
|
|
|
draw
|
|
|
|
|
traversals have been designed to cache rendering data locally and use
|
|
|
|
|
the
|
|
|
|
|
scene graph almost entirely as a read-only operation. This allows
|
|
|
|
|
multiple
|
|
|
|
|
cull-draw pairs to run on multiple CPU's which are bound to multiple
|
|
|
|
|
graphics
|
|
|
|
|
subsystems. Support for multiple graphic context and multi-threading is
|
|
|
|
|
all
|
|
|
|
|
available out of the box via osgProducer - all the examples in the
|
|
|
|
|
distribution
|
2003-04-25 03:54:03 +08:00
|
|
|
can run multi-pipe just by use a simple configuation file.
|
|
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|
|
</ul>
|
2003-11-25 17:23:04 +08:00
|
|
|
All the source to the OSG is published under the Open Scene Graph
|
|
|
|
|
Public License
|
|
|
|
|
(a relaxed version on the LGPL) which allows both open source and
|
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|
|
closed source projects to use,
|
|
|
|
|
modify and distribute it freely as long its usage complies with the
|
|
|
|
|
OSGPL.
|
|
|
|
|
The project has been developed over the last four years, initiated by
|
|
|
|
|
Don
|
|
|
|
|
Burns, and then taken over by Robert Osfield who continues to lead the
|
|
|
|
|
project
|
|
|
|
|
today. There are many other contributors to the library, for a full
|
|
|
|
|
list
|
|
|
|
|
check out the AUTHORS file. Both Robert and Don now work on the
|
|
|
|
|
OpenSceneGraph
|
|
|
|
|
in a professional capacity providing consultancy and bespoke
|
|
|
|
|
development
|
2002-04-25 14:27:09 +08:00
|
|
|
on top the library, and are also collaborating on the book. Work on the
|
2003-11-25 17:23:04 +08:00
|
|
|
core scene graph and support of public mailing list remains unpaid as
|
|
|
|
|
are
|
|
|
|
|
the contributions of the rest of the community, but this hasn't
|
|
|
|
|
impacted
|
|
|
|
|
the quality of the source or support which once you get stuck in you
|
|
|
|
|
grow
|
2002-04-25 14:27:09 +08:00
|
|
|
to appreciate.
|
2003-11-25 17:23:04 +08:00
|
|
|
<p>The project is currently in beta, which means the main core features
|
|
|
|
|
are now in
|
|
|
|
|
place, with a 1.0 release in second half of 2003. Despite the beta
|
|
|
|
|
development status,
|
|
|
|
|
the project has already earned the reputation as the leading open
|
|
|
|
|
source scene
|
|
|
|
|
graph, and is establishing itself as a viable alternative to the
|
|
|
|
|
commercial
|
|
|
|
|
scene graphs. Numerous companies, university researchers and graphics
|
|
|
|
|
enthusiasts
|
|
|
|
|
have already adopted the OpenSceneGraph for their projects, all over
|
|
|
|
|
the world. Examples of the wide variety of applications already
|
|
|
|
|
developed ontop of the OpenSceneGraph include <a
|
|
|
|
|
href="http://http://www.andesengineering.com/BlueMarbleViewer/">Blue
|
|
|
|
|
Marble Viewer</a>, <a href="http://www.vterrain.org"> Virtual Terrain
|
|
|
|
|
Project</a>, <a href="http://http://csp.sourceforge.net/">Combat
|
|
|
|
|
Simulator Project</a>, <a href="http://osgedit.sourceforge.net/">OSG-Edit</a>.
|
|
|
|
|
This is just a snippet of the projects that use the project, more
|
|
|
|
|
examples can be found on the screenshot pages and bazaar on the
|
|
|
|
|
website.
|
2003-04-28 19:37:53 +08:00
|
|
|
</p>
|
2002-04-25 14:27:09 +08:00
|
|
|
<h3>
|
|
|
|
|
<u>Getting started</u></h3>
|
2003-11-25 17:23:04 +08:00
|
|
|
The first thing is to select the distribution which suits you, there
|
|
|
|
|
are
|
2002-04-25 14:27:09 +08:00
|
|
|
binary, development and source code distributions, these can be loaded
|
|
|
|
|
from the
|
|
|
|
|
<a href="http://www.openscenegraph.org/download">http://www.openscenegraph.org/download</a>
|
2003-11-25 17:23:04 +08:00
|
|
|
page. The latest developments area available as via a nightly tarball
|
|
|
|
|
or
|
2002-04-25 14:27:09 +08:00
|
|
|
via cvs.
|
|
|
|
|
<p>The binary distribution contains just the libraries (.dll's /.so's)
|
2003-11-25 17:23:04 +08:00
|
|
|
and example executables. This is suitable for using the OpenSceneGraph
|
|
|
|
|
with
|
2002-04-25 14:27:09 +08:00
|
|
|
an application that has already been compiled but depends at runtime on
|
|
|
|
|
the OpenSceneGraph.
|
2003-04-25 03:54:03 +08:00
|
|
|
</p>
|
2002-04-25 14:27:09 +08:00
|
|
|
<p>The development distribution contains the libraries (.dll's /.so's),
|
2003-11-25 17:23:04 +08:00
|
|
|
example executables, include files, and source to the examples. This is
|
|
|
|
|
suitable
|
2003-04-28 19:37:53 +08:00
|
|
|
for developers using the OpenSceneGraph.
|
2003-04-25 03:54:03 +08:00
|
|
|
</p>
|
2002-05-22 03:34:16 +08:00
|
|
|
<p>The source distribution contains all the source and include files
|
2002-04-25 14:27:09 +08:00
|
|
|
required to build the OpenSceneGraph from scratch, and is ideal if you
|
2003-11-25 17:23:04 +08:00
|
|
|
want to learn more about how the scene graph works, how to extend it,
|
|
|
|
|
and
|
2002-05-22 03:34:16 +08:00
|
|
|
to track down and fix any problems that you come across.
|
2003-04-25 03:54:03 +08:00
|
|
|
</p>
|
2003-11-25 17:23:04 +08:00
|
|
|
<p>If you are using a source distribution then read the <a
|
|
|
|
|
href="install.html">installation</a>
|
2002-04-25 14:27:09 +08:00
|
|
|
instructions for how to get the OpenSceneGraph compiling and installed
|
2003-11-25 17:23:04 +08:00
|
|
|
on your system. You may also need to download libraries that parts of
|
|
|
|
|
the
|
|
|
|
|
OpenSceneGraph depend upon, such as Producer. Check the <a
|
|
|
|
|
href="dependencies.html">dependencies</a>
|
2002-04-25 14:27:09 +08:00
|
|
|
list for further details.
|
2003-04-25 03:54:03 +08:00
|
|
|
</p>
|
2003-11-25 17:23:04 +08:00
|
|
|
<p>For full instructions of how to run the examples read the <a
|
|
|
|
|
href="examples.html">examples</a>
|
2002-04-25 21:26:33 +08:00
|
|
|
page.
|
2003-04-25 03:54:03 +08:00
|
|
|
</p>
|
2002-04-25 14:27:09 +08:00
|
|
|
<h3>
|
2002-05-22 03:34:16 +08:00
|
|
|
<u>Learning how to use the OpenSceneGraph</u></h3>
|
2003-11-25 17:23:04 +08:00
|
|
|
<p>The OpenSceneGraph distribution comes with a reference guide for
|
|
|
|
|
each of
|
|
|
|
|
the component libraries - osg, osgDB, osgUtil, osgText, osgSim,
|
|
|
|
|
osgParticle and osgProducer, a set
|
|
|
|
|
of 42 examples - the source of which can be found in examples/
|
|
|
|
|
directory in the distribution. For questions
|
|
|
|
|
or help which can't be easily be answered by the reference guide and
|
|
|
|
|
examples
|
|
|
|
|
source, one should join the mailing list (details below). There are
|
|
|
|
|
also
|
|
|
|
|
the beginnings of a <a
|
|
|
|
|
href="http://www.c2.com/cgi/wiki?OpenSceneGraphFaq">Wiki
|
2002-04-25 14:27:09 +08:00
|
|
|
based FAQ</a> which may help answer a few of the common queries.
|
2003-04-25 03:54:03 +08:00
|
|
|
</p>
|
2003-11-25 17:23:04 +08:00
|
|
|
<p>A programming guide will be available in form of a OpenSceneGraph
|
|
|
|
|
book
|
|
|
|
|
which is being written by Don Burns and Robert Osfield, parts of it
|
|
|
|
|
will
|
2002-04-25 14:27:09 +08:00
|
|
|
be available online.
|
2003-04-25 03:54:03 +08:00
|
|
|
</p>
|
2002-04-25 14:27:09 +08:00
|
|
|
<p>Although not directly related to the OpenSceneGraph, once can learn
|
2003-11-25 17:23:04 +08:00
|
|
|
about scene graph technology from such sources as the <a
|
|
|
|
|
href="http://www.sgi.com/software/inventor/manuals.html">Open
|
|
|
|
|
Inventor Mentor</a>, and <a
|
|
|
|
|
href="http://www.cineca.it/manuali/Performer/ProgGuide24/html">Performer
|
2002-05-22 03:34:16 +08:00
|
|
|
Programming Guides</a>. The latter is the closer in design to
|
2003-11-25 17:23:04 +08:00
|
|
|
the OpenSceneGraph, although the Performer manuals are in C, alas. Also
|
|
|
|
|
of use
|
|
|
|
|
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
|
2002-04-25 14:27:09 +08:00
|
|
|
course</a>.
|
2003-04-25 03:54:03 +08:00
|
|
|
</p>
|
2003-11-25 17:23:04 +08:00
|
|
|
<p>The OpenSceneGraph uses OpenGL and does so with a deliberately thin
|
|
|
|
|
layer,
|
|
|
|
|
making it easy to control the underlying OpenGL and to extend it with
|
|
|
|
|
OpenGL
|
|
|
|
|
extensions. The close tie with OpenGL is also reflected in the naming
|
|
|
|
|
of
|
2002-05-22 03:34:16 +08:00
|
|
|
many of the OpenGL state related classes, and the parameters that they
|
2003-11-25 17:23:04 +08:00
|
|
|
encapsulate, which means that knowledge of OpenGL itself will go a long
|
|
|
|
|
way
|
2002-04-25 14:27:09 +08:00
|
|
|
to understanding how to get the best out of the OpenSceneGraph. To this
|
2003-11-25 17:23:04 +08:00
|
|
|
end it is worth obtaining a copy of the OpenGL programming guide - <a
|
|
|
|
|
href="http://fly.cc.fer.hr/%7Eunreal/theredbook/">`Red
|
|
|
|
|
Book`</a> and OpenGL reference guide 'Blue Book'. The main <a
|
|
|
|
|
href="http://www.opengl.org">OpenGL
|
2002-04-25 14:27:09 +08:00
|
|
|
website</a> is also a good source of links and further information.
|
2003-04-25 03:54:03 +08:00
|
|
|
</p>
|
2002-04-25 14:27:09 +08:00
|
|
|
<h3>
|
2003-11-25 17:23:04 +08:00
|
|
|
<u>Support and discussion - the <i>osg-user</i> mailing list</u></h3>
|
2002-04-25 14:27:09 +08:00
|
|
|
For scene graph related questions, bug reports, bug fixes, and general
|
2003-11-25 17:23:04 +08:00
|
|
|
design and development discussion one should join the <a
|
|
|
|
|
href="http://dburns.dhs.org/mailman/listinfo/osg-user"><span
|
|
|
|
|
style="text-decoration: underline;">osg-user</span></a>
|
|
|
|
|
mailing list, and check the the mailing list <a
|
|
|
|
|
href="http://osgcvs.no-ip.com/osgarchiver/">archives</a>.
|
|
|
|
|
<p>Professional support is also available in the form of confidential
|
|
|
|
|
online,
|
|
|
|
|
phone and onsite support and consultancy, for details contact Robert
|
|
|
|
|
Osfield
|
2002-04-25 14:27:09 +08:00
|
|
|
at <a href="mailto:robert@openscenegraph.com">robert@openscenegraph.com</a>.
|
2003-11-25 17:23:04 +08:00
|
|
|
</p>
|
2002-04-19 05:29:31 +08:00
|
|
|
</body>
|
2002-04-24 21:08:30 +08:00
|
|
|
</html>
|
