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| 6 | <title>Introduction to the OpenSceneGraph</title> |
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| 7 | </head> |
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| 8 | <body bgcolor="#FFFFFF"> |
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| 9 | <img SRC="images/OpenSceneGraphBanner_Distribution.jpg" BORDER=0> |
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| 10 | <table> |
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| 11 | <tr> |
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| 12 | <td><a href="index.html">Index</a></td> |
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| 13 | |
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| 14 | <td><a href="introduction.html">Introduction</a></td> |
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| 15 | |
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| 16 | <td><a href="contents.html">Contents</a></td> |
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| 17 | |
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| 18 | <td><a href="install.html">Install</a></td> |
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| 19 | |
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| 20 | <td><a href="dependencies.html">Dependencies</a></td> |
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| 21 | |
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| 22 | <td><a href="examples.html">examples</a></td> |
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| 23 | |
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| 24 | <td><a href="data.html">Data</a></td> |
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| 25 | |
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| 26 | <td><a href="osgviewer.html">Viewer</a></td> |
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| 27 | |
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| 28 | <td><a href="stereo.html">Stereo</a></td> |
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| 29 | |
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| 30 | <td><a href="plan.html">Plan</a></td> |
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| 31 | |
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| 32 | <td><a href="documentation.html">Reference Guides</a></td> |
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| 33 | </tr> |
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| 34 | </table> |
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| 35 | |
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| 36 | <h2> |
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| 37 | <u>Introduction to the OpenSceneGraph</u></h2> |
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| 38 | Welcome to OpenSceneGraph project! |
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| 39 | <p>The OpenSceneGraph is an Open Source <a href="../LICENSE.txt">(OSGPL)</a>, Cross Platform (Windows, |
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| 40 | Linux, Mac OSX, FreeBSD, Irix, Solaris and HP-UX), Standard C++ and OpenGL based |
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| 41 | graphics development library. Uses range from visual simulation, games, |
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| 42 | virtual reality, scientific visualization and graphics research. This page |
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| 43 | introduces what scene graphs are, why graphics developers use them, and |
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| 44 | details about the OpenSceneGraph project, how to learn how to use it and |
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| 45 | contribute to the OpenSceneGraph community. |
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| 46 | <p><i>Robert Osfield, Project Lead. July 2002.</i> |
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| 47 | <br> |
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| 48 | <hr> |
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| 49 | <h3> |
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| 50 | <u>What is a Scene Graph?</u></h3> |
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| 51 | Its a tree! Quite simply one the best and most reusable data structures |
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| 52 | invented. Typically drawn schematically with the root at the top, leaves at the |
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| 53 | bottom. It all starts with a top-most root node which encompasses your whole |
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| 54 | virtual world, be it 2D or 3D. The world is then broken down into a hierarchy |
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| 55 | of nodes representing either spatial groupings of objects, settings of the |
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| 56 | position of objects, animations of objects, or definitions of logical relationships |
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| 57 | between objects such as those to manage the various states of a traffic light. |
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| 58 | The leaves of the graph represent the physical objects themselves, the |
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| 59 | drawable geometry and their material properties. |
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| 60 | <p>A scene graph isn't a complete game or simulation engine, although it may |
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| 61 | be one of the main components of such an engine; it's primary focus is |
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| 62 | representation of your 3d worlds, and efficient rendering thereof. Physics models, |
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| 63 | collision detection and audio are left to other development libraries that |
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| 64 | a user will integrate with. The fact that scene graphs don't typically |
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| 65 | integrate all these features is actually a really good thing: it aids interoprability |
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| 66 | with clients' own applications and tools and allows them to serve many varied |
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| 67 | markets from games, visual simulation, virtual reality, |
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| 68 | scientific and commercial visualization, training through to modeling programs. |
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| 69 | <br> |
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| 70 | <hr> |
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| 71 | <h3> |
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| 72 | <u>Why use a Scene Graph - Performance, Productivity, Portability and Scalability</u>.</h3> |
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| 73 | |
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| 74 | <ol><b><i>Performance</i></b> - scene graphs provide an excellent framework for |
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| 75 | maximizing graphics performance. A good scene graph employs two key techniques |
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| 76 | - culling of the objects that won't be seen on screen, and state sorting |
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| 77 | of properties such as textures and materials, so that all similar objects |
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| 78 | are drawn together. Without culling the CPU, buses and GPU will all become |
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| 79 | swamped by many times the amount of data than they actually require to |
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| 80 | represent your work accurately. The hierarchical structure of the scene |
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| 81 | graph makes this culling process very efficient with whole town being culled |
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| 82 | with just a few operations! Without state sorting, the the buses and GPU |
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| 83 | will thrash between states, stalling the graphics pipeline and destroying graphics |
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| 84 | througput. As GPU's get faster and faster, the cost of stalling the graphics |
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| 85 | is also going up, so scene graphs are becoming ever more important. |
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| 86 | <p><b><i>Productivity</i></b> - scene graphs take away much of the hard work required |
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| 87 | to develop high performance graphics applications. The scene graph manages |
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| 88 | all the graphics for you, reducing what would be thousands of lines of |
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| 89 | OpenGL down to a few simple calls. Furthermore, one of most powerful concepts |
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| 90 | in Object Oriented programming is that of object composition, enshrined |
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| 91 | in the <i>Composite Design Pattern</i>, which fits the scene graph tree structure |
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| 92 | perfectly and makes it a highly flexible and reusable design - in real |
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| 93 | terms this means that it can be easily adapted to solve your problems. |
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| 94 | With scene graphs often also come additional utility libraries which range from |
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| 95 | helping users set up and manage graphics windows to importing of 3d models |
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| 96 | and images. All this together allows the user to achieve a great deal with |
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| 97 | very little coding. A dozen lines of code can be enough to load your data |
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| 98 | and create an interactive viewer! |
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| 99 | <p><b><i>Portability</i></b> - scene graphs encapsulate much of the lower level |
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| 100 | tasks of rendering graphics and reading and writing data, reducing or even |
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| 101 | eradicating the platform specific coding that you require in your own application. |
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| 102 | If the underlying scene graph is portable then moving from platform to |
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| 103 | platform can be as simple as recompiling your source code. |
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| 104 | <p><b><i>Scalability</i></b> - along with being able to dynamic manage the complexity |
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| 105 | of scenes automatically to account for differences in graphics performance |
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| 106 | across a range of machines, scene graphs also make it much easier to manage |
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| 107 | complex hardware configurations, such as clusters of graphics machines, |
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| 108 | or multiprocessor/multipipe systems such as SGI's Onyx. A good scene graph |
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| 109 | will allow the developer to concentrate on developing their own application |
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| 110 | while the rendering framework of the scene graph handles the different |
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| 111 | underlying hardware configurations.</ol> |
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| 112 | |
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| 113 | <hr> |
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| 114 | <h3> |
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| 115 | <u>So what about the OpenSceneGraph project?</u></h3> |
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| 116 | The OpenSceneGraph is an Open Source Scene Graph, and our goal is make |
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| 117 | the benefits of scene graph technology available to all. Our scene graph |
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| 118 | is still in development, but has already gained a great deal of respect |
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| 119 | amongst the development community for its high performance, cleanness of |
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| 120 | design and portability. Written entirely in Standard C++ and OpenGL, it |
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| 121 | makes full use of the STL and Design Patterns, and leverages the open source |
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| 122 | development model to provide a development library that is legacy free |
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| 123 | and well focused on the solving the task. The OpenSceneGraph delivers on |
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| 124 | the four key benefits of scene graph technology outlined above using the |
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| 125 | following features: |
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| 126 | <ol><b><i>Performance</i></b> - supports view frustum culling, occlusion culling, small feature culling, |
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| 127 | Level Of Detail (LOD) nodes, state sorting, vertex arrays and display |
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| 128 | lists as part of the core scene graph. These together make the OpenSceneGraph |
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| 129 | one of the highest performance scene graph available. User feedback is that |
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| 130 | performance surpasses that of much more established scene graphs such as Performer, VTree, Vega |
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| 131 | Scene Graph and Java3D! The OpenSceneGraph also supports easy customization |
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| 132 | of the drawing process, which has allowed implementation of Continuous Level |
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| 133 | of Detail (CLOD) meshes on top the scene graph. These allow the visualization |
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| 134 | of massive terrain databases interactively, examples of this approach can |
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| 135 | be found at Vterrain.org and TerrainEngine.com, both of which integrate |
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| 136 | with the OpenSceneGraph. |
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| 137 | <p><b><i>Productivity</i></b> - by combining lessons learned from established |
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| 138 | scene graphs like Performer and Open Inventor, with modern software engineering |
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| 139 | boosts like Design Patterns, along with a great deal of feedback early on |
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| 140 | in the development cycle, it has been possible to design a library that is |
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| 141 | clean and highly interpretable. This has made it easy for users to adopt |
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| 142 | to the OpenSceneGraph and to integrate it with their own applications. With |
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| 143 | a full feature set in the core scene graph, utilities to set up the scene |
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| 144 | graph and viewers and a wide range of loaders it is possible to create |
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| 145 | an application and bring in user data with a very small amount of code. |
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| 146 | <p><b><i>Portability</i></b> - The core scene graph has also been designed to |
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| 147 | have minimal dependency on any specific platform, requiring little more than |
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| 148 | Standard C++ and OpenGL. This has allowed the scene graph to be rapidly |
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| 149 | ported to a wide range of platforms - originally developed on IRIX, then |
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| 150 | ported to Linux, then to Windows, then FreeBSD, Mac OSX, Solaris, HP-UX and |
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| 151 | even a report of successful porting to PlayStation2! |
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| 152 | <p> |
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| 153 | The core scene graph library being completely windowing system independent makes |
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| 154 | it easy for users to add their own window-specific libraries and applications on top. |
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| 155 | 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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| 156 | found at openscenegrph.org/download/ one can find examples of applications |
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| 157 | written on top of Qt, MFC, WxWindows and SDL. Users have also integrated it |
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| 158 | with Motif, and X. |
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| 159 | <p><b><i>Scalability</i></b> - the scene graph will not only run on portables all |
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| 160 | the way up to Onyx Infinite Reality Monsters, it supports the multiple |
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| 161 | graphics subsystems found on machines like a mulitpipe Onyx. This is |
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| 162 | possible because the core scene graph supports multiple graphics contexts |
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| 163 | for both OpenGL Display Lists and texture objects, and the cull and draw |
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| 164 | traversals have been designed to cache rendering data locally and use the |
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| 165 | scene graph almost entirely as a read-only operation. This allows multiple |
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| 166 | cull-draw pairs to run on multiple CPU's which are bound to multiple graphics |
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| 167 | subsystems. Support for multiple graphic context and multi-threading is all |
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| 168 | available out of the box via osgProducer - all the examples in the distribution |
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| 169 | can run multi-pipe just by use a simple configuation file.</ol> |
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| 170 | |
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| 171 | All the source to the OSG is published under the Open Scene Graph Public License |
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| 172 | (a relaxed version on the LGPL) which allows both open source and closed source projects to use, |
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| 173 | modify and distribute it freely as long its usage complies with the OSGPL. |
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| 174 | The project has been developed over the last four years, initiated by Don |
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| 175 | Burns, and then taken over by Robert Osfield who continues to lead the project |
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| 176 | today. There are many other contributors to the library, for a full list |
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| 177 | check out the AUTHORS file. Both Robert and Don now work on the OpenSceneGraph |
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| 178 | in a professional capacity providing consultancy and bespoke development |
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| 179 | on top the library, and are also collaborating on the book. Work on the |
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| 180 | core scene graph and support of public mailing list remains unpaid as are |
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| 181 | the contributions of the rest of the community, but this hasn't impacted |
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| 182 | the quality of the source or support which once you get stuck in you grow |
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| 183 | to appreciate. |
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| 184 | <p>The project is currently in beta, which means the main core features are now in |
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| 185 | place, with a 1.0 release in second half of 2003. Despite the beta development status, |
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| 186 | the project has already earned the reputation as the leading open source scene |
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| 187 | graph, and is establishing itself as a viable alternative to the commercial |
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| 188 | scene graphs. Numerous companies, university researchers and graphics enthusiasts |
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| 189 | have already adopted the OpenSceneGraph for their projects, all over the world. |
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| 190 | <br> |
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| 191 | <hr> |
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| 192 | <h3> |
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| 193 | <u>Getting started</u></h3> |
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| 194 | The first thing is to select the distribution which suits you, there are |
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| 195 | binary, development and source code distributions, these can be loaded |
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| 196 | from the |
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| 197 | <a href="http://www.openscenegraph.org/download">http://www.openscenegraph.org/download</a> |
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| 198 | page. The latest developments area available as via a nightly tarball or |
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| 199 | via cvs. |
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| 200 | <p>The binary distribution contains just the libraries (.dll's /.so's) |
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| 201 | and demo executables. This is suitable for using the OpenSceneGraph with |
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| 202 | an application that has already been compiled but depends at runtime on |
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| 203 | the OpenSceneGraph. |
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| 204 | <p>The development distribution contains the libraries (.dll's /.so's), |
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| 205 | demo executables, include files, and source to the demos. This is suitable |
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| 206 | for using the developers using the OpenSceneGraph. |
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| 207 | <p>The source distribution contains all the source and include files |
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| 208 | required to build the OpenSceneGraph from scratch, and is ideal if you |
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| 209 | want to learn more about how the scene graph works, how to extend it, and |
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| 210 | to track down and fix any problems that you come across. |
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| 211 | <p>If you are using a source distribution then read the <a href="install.html">installation</a> |
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| 212 | instructions for how to get the OpenSceneGraph compiling and installed |
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| 213 | on your system. You may also need to download libraries that parts of the |
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| 214 | OpenSceneGraph depend upon, such as Producer. Check the <a href="dependencies.html">dependencies</a> |
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| 215 | list for further details. |
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| 216 | <p>For full instructions of how to run the examples read the <a href="examples.html">examples</a> |
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| 217 | page. |
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| 218 | <br> |
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| 219 | <hr> |
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| 220 | <h3> |
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| 221 | <u>Learning how to use the OpenSceneGraph</u></h3> |
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| 222 | The OpenSceneGraph distribution comes with a reference guide for each of |
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| 223 | the component libraries - osg, osgDB, osgUtil, osgText, osgSim, osgParticle and osgProducer, a set |
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| 224 | of examples - the source of which can be found in examples. For questions |
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| 225 | or help which can't be easily be answered by the reference guide and demo |
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| 226 | source, one should join the mailing list (details below). There are also |
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| 227 | the beginnings of a <a href="http://www.c2.com/cgi/wiki?OpenSceneGraphFaq">Wiki |
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| 228 | based FAQ</a> which may help answer a few of the common queries. |
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| 229 | <p>A programming guide will be available in form of a OpenSceneGraph book |
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| 230 | which is being written by Don Burns and Robert Osfield, parts of it will |
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| 231 | be available online. |
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| 232 | <p>Although not directly related to the OpenSceneGraph, once can learn |
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| 233 | about scene graph technology from such sources as the <a href="http://www.sgi.com/software/inventor/manuals.html">Open |
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| 234 | Inventor Mentor</a>, and <a href="http://www.cineca.it/manuali/Performer/ProgGuide24/html">Performer |
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| 235 | Programming Guides</a>. The latter is the closer in design to |
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| 236 | the OpenSceneGraph, although the Performer manuals are in C, alas. Also of use |
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| 237 | 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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| 238 | course</a>. |
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| 239 | <p>The OpenSceneGraph uses OpenGL and does so with a deliberately thin layer, |
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| 240 | making it easy to control the underlying OpenGL and to extend it with OpenGL |
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| 241 | extensions. The close tie with OpenGL is also reflected in the naming of |
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| 242 | many of the OpenGL state related classes, and the parameters that they |
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| 243 | encapsulate, which means that knowledge of OpenGL itself will go a long way |
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| 244 | to understanding how to get the best out of the OpenSceneGraph. To this |
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| 245 | 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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| 246 | Book`</a> and OpenGL reference guide 'Blue Book'. The main <a href="http://www.opengl.org">OpenGL |
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| 247 | website</a> is also a good source of links and further information. |
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| 248 | <br> |
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| 249 | <hr> |
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| 250 | <h3> |
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| 251 | <u>Support and discussion - the <i>openscenegraph-news</i> mailing list</u></h3> |
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| 252 | For scene graph related questions, bug reports, bug fixes, and general |
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| 253 | 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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| 254 | mailing list, and check the the mailing list <a href="http://www.geocrawler.com/redir-sf.php3?list=openscenegraph-news">archives</a>. |
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| 255 | <p>Professional support is also available in the form of confidential online, |
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| 256 | phone and onsite support and consultancy, for details contact Robert Osfield |
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| 257 | at <a href="mailto:robert@openscenegraph.com">robert@openscenegraph.com</a>. |
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| 258 | </body> |
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| 259 | </html> |
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