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| 8 | <title>Introduction to the OpenSceneGraph</title> |
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| 9 | </head> |
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| 10 | <body bgcolor="#ffffff"> |
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| 11 | <img src="images/OpenSceneGraphBanner_Distribution.jpg" border="0"> |
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| 12 | <table> |
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| 13 | <tbody> |
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| 14 | <tr> |
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| 15 | <td><a href="index.html">Index</a></td> |
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| 16 | <td><a href="introduction.html">Introduction</a></td> |
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| 17 | <td><a href="contents.html">Contents</a></td> |
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| 18 | <td><a href="install.html">Install</a></td> |
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| 19 | <td><a href="dependencies.html">Dependencies</a></td> |
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| 20 | <td><a href="examples.html">examples</a></td> |
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| 21 | <td><a href="data.html">Data</a></td> |
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| 22 | <td><a href="osgviewer.html">Viewer</a></td> |
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| 23 | <td><a href="stereo.html">Stereo</a></td> |
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| 24 | <td><a href="osgdem.html">osgdem</a></td> |
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| 25 | <td><a href="plan.html">Plan</a></td> |
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| 26 | <td><a href="documentation.html">Reference Guides</a></td> |
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| 27 | </tr> |
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| 28 | </tbody> |
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| 29 | </table> |
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| 30 | <h2> |
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| 31 | <u>Introduction to the OpenSceneGraph</u></h2> |
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| 32 | <p>The OpenSceneGraph is an portable, high level graphics toolkit for |
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| 33 | the development of high peformance |
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| 34 | graphics applications such as flight simulators, games, virtual reality |
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| 35 | or scientific visualization. Providing an object orientated framework |
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| 36 | on top of OpenGL, it frees the developer |
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| 37 | from implementing and optimizing low level graphics calls, and provide |
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| 38 | many additional utilities for rapid development of graphics |
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| 39 | applications. </p> |
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| 40 | <p> |
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| 41 | The project was started as a hobby by Don Burns in 1998, as means of |
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| 42 | porting a hang gliding simulator written on top of the Performer scene |
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| 43 | graph running on IRIX to what was then a humble Linux PC. In 1999, |
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| 44 | Robert Osfield began helping out with the simulator development and |
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| 45 | ported the scene graph element to Windows. In september 1999 the source |
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| 46 | code was open sourced, and the openscenegraph.org website was born, |
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| 47 | with Robert taking over as project lead and Don remaining focused on |
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| 48 | the hang gliding simulator. |
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| 49 | </p> |
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| 50 | <p> In April 2001, in response to growing interest in the project |
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| 51 | around the world, Robert went fulltime on the project, setting up <a |
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| 52 | href="http://www.openscenegraph.com">OpenSceneGraph Professional |
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| 53 | Services</a> providing commericial support, consultancy services and |
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| 54 | training. At the end of 2001 Don also formed his own company <a |
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| 55 | href="http://www.andesengineering.com">Andes Computer Engineering</a> |
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| 56 | and participates in the development and support of OpenSceneGraph as |
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| 57 | well as complimentary projects like <a |
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| 58 | href="http://www.andesengineering.com/Producer">OpenProducer</a> and <a |
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| 59 | href="http://www.andesengineering.com/BlueMarbleViewer">BlueMarbleViewer</a>. |
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| 60 | </p> |
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| 61 | <h3><u>What is a Scene Graph?</u></h3> |
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| 62 | Its a tree! Quite simply one the best and most reusable data structures |
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| 63 | invented. Typically drawn schematically with the root at the top, |
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| 64 | leaves at the |
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| 65 | bottom. It all starts with a top-most root node which encompasses your |
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| 66 | whole |
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| 67 | virtual world, be it 2D or 3D. The world is then broken down into a |
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| 68 | hierarchy |
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| 69 | of nodes representing either spatial groupings of objects, settings of |
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| 70 | the |
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| 71 | position of objects, animations of objects, or definitions of logical |
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| 72 | relationships |
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| 73 | between objects such as those to manage the various states of a traffic |
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| 74 | light. |
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| 75 | The leaves of the graph represent the physical objects themselves, the |
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| 76 | drawable geometry and their material properties. |
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| 77 | <p></p> |
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| 78 | <p>A scene graph isn't a complete game or simulation engine, although |
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| 79 | it may |
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| 80 | be one of the main components of such an engine; it's primary focus is |
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| 81 | representation of your 3d worlds, and efficient rendering thereof. |
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| 82 | Physics models, |
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| 83 | collision detection and audio are left to other development libraries |
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| 84 | that |
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| 85 | a user will integrate with. The fact that scene graphs don't typically |
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| 86 | integrate all these features is actually a really good thing: it aids |
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| 87 | interoprability |
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| 88 | with clients' own applications and tools and allows it to serve many |
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| 89 | varied |
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| 90 | markets from games, visual simulation, virtual reality, |
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| 91 | scientific and commercial visualization, training through to modeling |
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| 92 | programs. |
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| 93 | </p> |
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| 94 | <h3> |
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| 95 | <u>Benefits that Scene Graphs provide</u></h3> |
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| 96 | The key reasons that many graphics developers uses scene graphs are <i>Performance, |
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| 97 | Productivity, Portability and Scalability:</i> |
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| 98 | <ul> |
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| 99 | <li><b><i>Performance</i></b></li> |
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| 100 | Scene graphs provide an excellent framework for |
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| 101 | maximizing graphics performance. A good scene graph employs two key |
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| 102 | techniques |
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| 103 | - culling of the objects that won't be seen on screen, and state |
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| 104 | sorting |
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| 105 | of properties such as textures and materials, so that all similar |
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| 106 | objects |
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| 107 | are drawn together. Without culling the CPU, buses and GPU will all |
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| 108 | become |
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| 109 | swamped by many times the amount of data than they actually require to |
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| 110 | represent your scenes accurately. The hierarchical structure of the |
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| 111 | scene |
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| 112 | graph makes this culling process very efficient, for instance a whole |
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| 113 | city can be culled |
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| 114 | with just a few operations! Without state sorting, the the buses and |
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| 115 | GPU |
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| 116 | will thrash between states, stalling the graphics pipeline and |
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| 117 | destroying graphics |
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| 118 | throughput. As GPU's get faster and faster, the cost of stalling the |
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| 119 | graphics pipeline |
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| 120 | is also going up, so scene graphs are becoming ever more important. |
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| 121 | <p></p> |
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| 122 | <li><b><i>Productivity</i></b></li> |
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| 123 | Scene graphs take away much of the hard work required |
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| 124 | to develop high performance graphics applications. The scene graph |
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| 125 | manages |
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| 126 | all the graphics for you, reducing what would be thousands of lines of |
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| 127 | OpenGL down to a few simple calls. Furthermore, one of most powerful |
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| 128 | concepts |
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| 129 | in Object Oriented programming is that of object composition, enshrined |
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| 130 | in the <i>Composite Design Pattern</i>, which fits the scene graph |
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| 131 | tree structure |
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| 132 | perfectly and makes it a highly flexible and reusable design - in real |
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| 133 | terms this means that it can be easily adapted to solve your problems. |
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| 134 | Scene graphs also often come additional utility libraries which range |
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| 135 | from |
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| 136 | helping users set up and manage graphics windows to importing of 3d |
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| 137 | models |
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| 138 | and images. All this together allows the user to achieve a great deal |
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| 139 | with |
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| 140 | very little coding. A dozen lines of code can be enough to load your |
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| 141 | data |
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| 142 | and create an interactive viewer! |
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| 143 | <p></p> |
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| 144 | <li><b><i>Portability</i></b></li> |
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| 145 | Scene graphs encapsulate much of the lower level |
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| 146 | tasks of rendering graphics and reading and writing data, reducing or |
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| 147 | even |
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| 148 | eradicating the platform specific coding that you require in your own |
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| 149 | application. |
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| 150 | If the underlying scene graph is portable then moving from platform to |
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| 151 | platform can be as simple as recompiling your source code. |
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| 152 | <p></p> |
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| 153 | <li><b><i>Scalability</i></b></li> |
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| 154 | Along with being able to dynamic manage the complexity |
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| 155 | of scenes automatically to account for differences in graphics |
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| 156 | performance |
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| 157 | across a range of machines, scene graphs also make it much easier to |
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| 158 | manage |
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| 159 | complex hardware configurations, such as clusters of graphics machines, |
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| 160 | or multiprocessor/multipipe systems such as SGI's Onyx. A good scene |
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| 161 | graph |
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| 162 | will allow the developer to concentrate on developing their own |
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| 163 | application |
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| 164 | while the rendering framework of the scene graph handles the different |
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| 165 | underlying hardware configurations. |
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| 166 | </ul> |
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| 167 | <h3> |
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| 168 | <u>The OpenSceneGraph - <i> a robust, high peformance Open Source |
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| 169 | scene graph</i></u></h3> |
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| 170 | With the OpenSceneGraph our goal is make the benefits of scene graph |
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| 171 | technology freely available to all, for both commericial and non |
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| 172 | commericial users. Whilst our scene graph |
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| 173 | is still in development, it has already gained a respect |
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| 174 | amongst the development community for its high performance, cleanness |
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| 175 | of |
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| 176 | design and portability. Written entirely in Standard C++ and OpenGL, it |
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| 177 | makes full use of the STL and Design Patterns, and leverages the open |
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| 178 | source |
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| 179 | development model to provide a development library that is legacy free |
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| 180 | and focused on the needs of end users. The OpenSceneGraph delivers on |
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| 181 | the four key benefits of scene graph technology outlined above with the |
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| 182 | following features: |
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| 183 | <ul> |
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| 184 | <li><b><i>Performance</i></b></li> |
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| 185 | Supports view frustum culling, occlusion culling, small feature |
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| 186 | culling, |
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| 187 | Level Of Detail (LOD) nodes, state sorting, vertex arrays and display |
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| 188 | lists as part of the core scene graph. These together make the |
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| 189 | OpenSceneGraph |
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| 190 | one of the highest performance scene graph available. User feedback is |
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| 191 | that |
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| 192 | performance matches or surpasses that of much more established scene |
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| 193 | graphs such as Performer, VTree, Vega Scene Graph and Java3D! The |
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| 194 | OpenSceneGraph also supports easy customization |
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| 195 | of the drawing process, which has allowed implementation of Continuous |
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| 196 | Level |
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| 197 | of Detail (CLOD) meshes on top the scene graph. These allow the |
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| 198 | visualization |
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| 199 | of massive terrain databases interactively, examples of this approach |
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| 200 | can |
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| 201 | be found at Vterrain.org and TerrainEngine.com, both of which integrate |
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| 202 | with the OpenSceneGraph. |
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| 203 | <p></p> |
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| 204 | <li><b><i>Productivity</i></b> </li> |
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| 205 | <p>The core scene graph provides encapsulate the majority of OpenGL |
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| 206 | functionality including latest extensions, provides rending |
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| 207 | optimizations |
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| 208 | such as culling and sorting, and a whole set of add on libraries which |
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| 209 | make |
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| 210 | it possible to develop high peformance graphics applications very |
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| 211 | rapidly. The application developer is freed to concentrate on content |
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| 212 | and how that content is controlled rather than low level coding. </p> |
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| 213 | <p>Combining lessons learned from established scene graphs like |
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| 214 | Performer |
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| 215 | and Open Inventor, with modern software engineering methods like Design |
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| 216 | Patterns, along with a great deal of feedback early on in the |
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| 217 | development cycle, it has been possible to design a library that is |
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| 218 | clean and extensible. This has made it easy for users to adopt to the |
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| 219 | OpenSceneGraph and to integrate it with their own applications. </p> |
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| 220 | <p>For reading and writing databases an the database library (osgDB) |
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| 221 | adds |
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| 222 | support for a wide |
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| 223 | variety of database formats via a extensible dynamic plugin mechansim - |
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| 224 | the distribution now includes 33 |
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| 225 | seperate plugins for loading various 3D and Image data formats. 3D |
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| 226 | Database loaders include OpenFlight (.flt), TerraPage (.txp) including |
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| 227 | multi-threading support, LightWave (.lwo), Alias Wavefront (.obj), |
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| 228 | Carbon Graphics GEO (.geo), 3D Studio MAX (.3ds), Peformer (.pfb), |
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| 229 | Quake Character Models (.md2). Direct X (.x), and Inventor Ascii 2.0 |
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| 230 | (.iv)/ VRML 1.0 (.wrl), Designer Workshop (.dw) and AC3D (.ac) and the |
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| 231 | native .osg ASCII format. |
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| 232 | Image loaders include .rgb, .gif, .jpg, .png, .tiff, .pic, .bmp, .dds |
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| 233 | (include compressed mip mapped imagery), .tga and qucktime (under OSX). |
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| 234 | A whole set of high quality, anti-aliased fonts can also be loaded via |
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| 235 | the freetype plugin. </p> |
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| 236 | <p>The scene graph also has a set of <i>Node Kits</i> which are |
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| 237 | seperate |
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| 238 | libraries, |
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| 239 | that can be compiled in with your applications or loaded in at runtime, |
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| 240 | which add support for particle systems (osgParticle), |
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| 241 | high quality anti-aliased text (osgText) and navigational light points |
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| 242 | (osgSim). </p> |
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| 243 | <p>The community has also developed a number of additional <i>Node |
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| 244 | Kits</i> |
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| 245 | such as <a href="http://osgnv.sourceforge.net/">osgNV</a> (which |
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| 246 | includes support for NVidia's vertex, fragment, combiner etc extension |
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| 247 | and NVidia's Cg shader language.), <a |
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| 248 | href="http://www.terrainengine.com">Demeter</a> (CLOD terrain + |
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| 249 | integration with OSG). <a href="http://osgcal.sourceforge.net">osgCal</a> |
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| 250 | (which integrates <a href="http://cal3d.sourceforge.net//">Cal3D</a> |
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| 251 | and the OSG), <a href="http://www.vrlab.umu.se/research/osgvortex">osgVortex</a> |
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| 252 | (which integrates the <a href="http://www.cm-labs.com/">CM-Labs Vortex</a> |
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| 253 | physics enginer with OSG) |
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| 254 | and a whole set libraries that integrating the leading Windowing API's |
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| 255 | Links can be found in the bazaar sections on the <a |
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| 256 | href="http://www.openscenegraph.org/download/">download</a> page of |
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| 257 | OpenSceneGraph webiste. </p> |
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| 258 | <p>The project has also been integrated with <a |
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| 259 | href="http://www.vrjuggler.org/">VR Juggler</a> and <a |
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| 260 | href="http://http://vess.ist.ucf.edu/">Vess</a> virtual realilty the |
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| 261 | frameworks, with others in developments. </p> |
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| 262 | <li><b><i>Portability</i></b></li> |
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| 263 | The core scene graph has also been designed to |
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| 264 | have minimal dependency on any specific platform, requiring little more |
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| 265 | than |
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| 266 | Standard C++ and OpenGL. This has allowed the scene graph to be rapidly |
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| 267 | ported to a wide range of platforms - originally developed on IRIX, |
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| 268 | then |
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| 269 | ported to Linux, then to Windows, then FreeBSD, Mac OSX, Solaris, HP-UX |
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| 270 | and we even a report of successful porting to PlayStation2! <br> |
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| 271 | The core scene graph library being completely windowing system |
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| 272 | independent makes it easy for users to add their own window-specific |
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| 273 | libraries and applications on top. |
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| 274 | In the distribution there is already the osgProducer library which |
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| 275 | integrates with <a href="http://www.andesengineering.com/Producer/">OpenProducer</a>, |
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| 276 | and in the Bazaar |
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| 277 | found at openscenegrph.org/download/ one can find examples of |
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| 278 | applications |
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| 279 | written on top of GLUT, Qt, MFC, WxWindows and SDL. Users have also |
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| 280 | integrated it |
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| 281 | with Motif, and X. |
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| 282 | <p></p> |
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| 283 | <li><b><i>Scalability</i></b></li> |
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| 284 | The scene graph will not only run on portables all |
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| 285 | the way up to Onyx Infinite Reality Monsters, but also supports the |
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| 286 | multiple |
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| 287 | graphics subsystems found on machines like a mulitpipe Onyx. This is |
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| 288 | possible because the core scene graph supports multiple graphics |
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| 289 | contexts |
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| 290 | for both OpenGL Display Lists and texture objects, and the cull and |
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| 291 | draw |
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| 292 | traversals have been designed to cache rendering data locally and use |
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| 293 | the |
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| 294 | scene graph almost entirely as a read-only operation. This allows |
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| 295 | multiple |
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| 296 | cull-draw pairs to run on multiple CPU's which are bound to multiple |
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| 297 | graphics |
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| 298 | subsystems. Support for multiple graphic context and multi-threading is |
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| 299 | all |
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| 300 | available out of the box via osgProducer - all the examples in the |
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| 301 | distribution |
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| 302 | can run multi-pipe just by use a simple configuation file. |
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| 303 | </ul> |
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| 304 | All the source to the OSG is published under the Open Scene Graph |
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| 305 | Public License |
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| 306 | (a relaxed version on the LGPL) which allows both open source and |
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| 307 | closed source projects to use, |
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| 308 | modify and distribute it freely as long its usage complies with the |
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| 309 | OSGPL. |
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| 310 | The project has been developed over the last four years, initiated by |
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| 311 | Don |
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| 312 | Burns, and then taken over by Robert Osfield who continues to lead the |
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| 313 | project |
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| 314 | today. There are many other contributors to the library, for a full |
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| 315 | list |
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| 316 | check out the AUTHORS file. Both Robert and Don now work on the |
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| 317 | OpenSceneGraph |
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| 318 | in a professional capacity providing consultancy and bespoke |
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| 319 | development |
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| 320 | on top the library, and are also collaborating on the book. Work on the |
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| 321 | core scene graph and support of public mailing list remains unpaid as |
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| 322 | are |
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| 323 | the contributions of the rest of the community, but this hasn't |
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| 324 | impacted |
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| 325 | the quality of the source or support which once you get stuck in you |
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| 326 | grow |
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| 327 | to appreciate. |
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| 328 | <p>The project is currently in beta, which means the main core features |
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| 329 | are now in |
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| 330 | place, with a 1.0 release in second half of 2004. Despite the beta |
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| 331 | development status, |
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| 332 | the project has already earned the reputation as the leading open |
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| 333 | source scene |
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| 334 | graph, and is establishing itself as a viable alternative to the |
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| 335 | commercial |
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| 336 | scene graphs. Numerous companies, university researchers and graphics |
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| 337 | enthusiasts |
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| 338 | have already adopted the OpenSceneGraph for their projects, all over |
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| 339 | the world. Examples of the wide variety of applications already |
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| 340 | developed ontop of the OpenSceneGraph include <a |
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| 341 | href="http://http://www.andesengineering.com/BlueMarbleViewer/">Blue |
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| 342 | Marble Viewer</a>, <a href="http://www.vterrain.org"> Virtual Terrain |
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| 343 | Project</a>, <a href="http://http://csp.sourceforge.net/">Combat |
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| 344 | Simulator Project</a>, <a href="http://osgedit.sourceforge.net/">OSG-Edit</a>. |
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| 345 | This is just a snippet of the projects that use the project, more |
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| 346 | examples can be found on the screenshot pages and bazaar on the |
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| 347 | website. |
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| 348 | </p> |
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| 349 | <h3> |
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| 350 | <u>Getting started</u></h3> |
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| 351 | The first thing is to select the distribution which suits you, there |
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| 352 | are |
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| 353 | binary, development and source code distributions, these can be loaded |
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| 354 | from the |
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| 355 | <a href="http://openscenegraph.sf.net/downloads">http://openscenegraph.sf.net/downloads</a> |
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| 356 | page. The latest developments area available as via a nightly tarball |
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| 357 | or |
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| 358 | via cvs. |
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| 359 | <p>The binary distribution contains just the libraries (.dll's /.so's) |
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| 360 | and example executables. This is suitable for using the OpenSceneGraph |
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| 361 | with |
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| 362 | an application that has already been compiled but depends at runtime on |
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| 363 | the OpenSceneGraph. |
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| 364 | </p> |
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| 365 | <p>The development distribution contains the libraries (.dll's /.so's), |
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| 366 | example executables, include files, and source to the examples. This is |
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| 367 | suitable |
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| 368 | for developers using the OpenSceneGraph. |
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| 369 | </p> |
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| 370 | <p>The source distribution contains all the source and include files |
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| 371 | required to build the OpenSceneGraph from scratch, and is ideal if you |
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| 372 | want to learn more about how the scene graph works, how to extend it, |
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| 373 | and |
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| 374 | to track down and fix any problems that you come across. |
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| 375 | </p> |
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| 376 | <p>If you are using a source distribution then read the <a |
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| 377 | href="install.html">installation</a> |
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| 378 | instructions for how to get the OpenSceneGraph compiling and installed |
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| 379 | on your system. You may also need to download libraries that parts of |
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| 380 | the |
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| 381 | OpenSceneGraph depend upon, such as Producer. Check the <a |
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| 382 | href="dependencies.html">dependencies</a> |
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| 383 | list for further details. |
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| 384 | </p> |
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| 385 | <p>For full instructions of how to run the examples read the <a |
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| 386 | href="examples.html">examples</a> |
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| 387 | page. |
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| 388 | </p> |
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| 389 | <h3> |
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| 390 | <u>Learning how to use the OpenSceneGraph</u></h3> |
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| 391 | <p>The main collections of resources for learning how to use the |
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| 392 | OpenSceneGraph can be found on openscenegraph.org documentaiton page, |
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| 393 | please check this out regular for new entries.<br> |
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| 394 | </p> |
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| 395 | <p>The OpenSceneGraph distribution comes with a reference guide for |
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| 396 | each of |
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| 397 | the component libraries - osg, osgDB, osgUtil, osgText, osgSim, |
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| 398 | osgParticle and osgProducer, a set |
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| 399 | of 42 examples - the source of which can be found in examples/ |
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| 400 | directory in the distribution. For questions |
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| 401 | or help which can't be easily be answered by the reference guide and |
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| 402 | examples |
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| 403 | source, one should join the mailing list (details below). There are |
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| 404 | also |
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| 405 | the beginnings of a <a |
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| 406 | href="http://www.c2.com/cgi/wiki?OpenSceneGraphFaq">Wiki |
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| 407 | based FAQ</a> which may help answer a few of the common queries. |
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| 408 | </p> |
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| 409 | <p>Two sets of online tutorial been written by members of the |
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| 410 | OpenSceneGraph community:<br> |
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| 411 | Jason McVeigh's <a |
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| 412 | href="http://www.tersesolutions.net/osgt/">OpenSceneGraph Tutorials</a><br> |
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| 413 | Joseph Sullivan's <a |
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| 414 | href="http://www.nps.navy.mil/cs/sullivan/osgTutorials/index.html">OpenSceneGraph |
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| 415 | Tutorials</a><br> |
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| 416 | <br> |
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| 417 | A programming guide will be available in form of a OpenSceneGraph |
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| 418 | book |
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| 419 | which is being written by Don Burns and Robert Osfield, parts of it |
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| 420 | will |
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| 421 | be available online. |
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| 422 | </p> |
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| 423 | <p>Although not directly related to the OpenSceneGraph, once can learn |
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| 424 | about scene graph technology from such sources as the <a |
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| 425 | href="http://www.sgi.com/software/inventor/manuals.html">Open |
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| 426 | Inventor Mentor</a>, and <a |
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| 427 | href="http://www.cineca.it/manuali/Performer/ProgGuide24/html">Performer |
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| 428 | Programming Guides</a>. The latter is the closer in design to |
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| 429 | the OpenSceneGraph, although the Performer manuals are in C, alas. Also |
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| 430 | of use |
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| 431 | as a background to some of the techniques used is a SIGGRAPH <a |
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| 432 | href="http://www.opengl.org/developers/code/sig99/advanced99/course_slides/vissim/index.htm">Vis-Sim |
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| 433 | course</a>. |
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| 434 | </p> |
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| 435 | <p>The OpenSceneGraph uses OpenGL and does so with a deliberately thin |
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| 436 | layer, |
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| 437 | making it easy to control the underlying OpenGL and to extend it with |
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| 438 | OpenGL |
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| 439 | extensions. The close tie with OpenGL is also reflected in the naming |
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| 440 | of |
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| 441 | many of the OpenGL state related classes, and the parameters that they |
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| 442 | encapsulate, which means that knowledge of OpenGL itself will go a long |
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| 443 | way |
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| 444 | to understanding how to get the best out of the OpenSceneGraph. To this |
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| 445 | end it is worth obtaining a copy of the OpenGL programming guide - <a |
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| 446 | href="http://fly.cc.fer.hr/%7Eunreal/theredbook/">`Red |
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| 447 | Book`</a> and OpenGL reference guide 'Blue Book'. The main <a |
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| 448 | href="http://www.opengl.org">OpenGL |
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| 449 | website</a> is also a good source of links and further information. |
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| 450 | </p> |
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| 451 | <h3> |
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| 452 | <u>Support and discussion - the <i>osg-user</i> mailing list</u></h3> |
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| 453 | For scene graph related questions, bug reports, bug fixes, and general |
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| 454 | design and development discussion one should join the <a |
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| 455 | href="http://dburns.dhs.org/mailman/listinfo/osg-user"><span |
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| 456 | style="text-decoration: underline;">osg-user</span></a> |
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| 457 | mailing list, and check the the mailing list <a |
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| 458 | href="http://osgcvs.no-ip.com/osgarchiver/">archives</a>. |
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| 459 | <p>Professional support is also available in the form of confidential |
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| 460 | online, |
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| 461 | phone and onsite support and consultancy, for details contact Robert |
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| 462 | Osfield |
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| 463 | at <a href="mailto:robert@openscenegraph.com">robert@openscenegraph.com</a>. |
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| 464 | </p> |
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| 465 | </body> |
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| 466 | </html> |
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