88 lines
4.2 KiB
HTML
88 lines
4.2 KiB
HTML
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
|
||
|
|
<html>
|
||
|
|
<head>
|
||
|
|
<title>introduction to the OpenSceneGraph</title>
|
||
|
|
</head>
|
||
|
|
<body bgcolor="white">
|
||
|
|
|
||
|
|
<img src="OpenSceneGraphBanner_Distribution.jpg" width=640 height=77 border=0>
|
||
|
|
|
||
|
|
<h2>Introduction to the OpenSceneGraph</h2>
|
||
|
|
|
||
|
|
<p>Welcome to OpenSceneGraph project!
|
||
|
|
</p>
|
||
|
|
<p>In this document I'll introduce what a scene graph is, what the OpenSceneGraph project encompasses, and provide tips on how to learn how to use it
|
||
|
|
and to contact or contribute to the OpenSceneGraph community.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<i>Robert Osfield,
|
||
|
|
Project Lead.
|
||
|
|
April 2002.</i>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
|
||
|
|
<h2>What is a Scene Graph?</h2>
|
||
|
|
</p>Its a tree! Quite simply one the best and most reusable datastructures invented.Typically drawn schematically as
|
||
|
|
root at the top, leaves at the bottom. It all starts with a topmost root node which
|
||
|
|
encompasses your whole virtual world, be it 2D or 3D. The world is then broken down
|
||
|
|
into hierachy of nodes represent either a spatial grouping of objects,
|
||
|
|
set the position of or animate objects,. or define a logical relationship between objects such as to manage
|
||
|
|
the various states of a traffic light.The leaves of the graph represent the phyical objects
|
||
|
|
themselves, the drawable geometry and their material properties.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
|
||
|
|
<h2>Why use a Scene Graph - Performance, Productivity, Portability and Scalability.</h2>
|
||
|
|
|
||
|
|
</p><i>Performance</i> - scene graphs provide an excellent framework for maximize graphics
|
||
|
|
performance. A good scene graph employs two key techinques - culling of the objects that won't
|
||
|
|
be seen on screen, and state sorting of properties such as textures and materials
|
||
|
|
so that all similar objects are drawn together. Without culling the CPU, buses and
|
||
|
|
GPU will all become swamped by many times the amount of data tham they acual require.to represent
|
||
|
|
you work accurately. The hierachical structure of the scene graph makes this culling
|
||
|
|
process.very efficient.with whole town being culled with just a few operations! Without state storting, the the buses and GPU will thrash between
|
||
|
|
states, stalling the graphics and destroying graphisc throughout. As GPU's get faster and faster, the cost of
|
||
|
|
stalling the graphics is also going up, so scene graph are become ever more important.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
</p><i>Productivity</i> - scene graphs take much of the hardwork required to develop
|
||
|
|
high perftomance graphics applications. The scene graphs manage all the graphics for you,
|
||
|
|
reducing what would be thousands of lines of OpenGL down to a few simple calls..Furthermoe,
|
||
|
|
one of most powerfukl concepts in Object Orientated programming is that of object
|
||
|
|
compotsition, enshrined in <i>Composite Design Pattern</i>, which fits the scene graph
|
||
|
|
tree strucutre perfectly which makes it highly flexible and reusable design - in real terms
|
||
|
|
this means that it can be easily adapted it to solve your problems. Scene graph also often come
|
||
|
|
additional utilitie libraries which range for helping users set up and manage graphics
|
||
|
|
windows to import of 3d modes and images. All this together allows the user to achieve
|
||
|
|
a great deal with very little coding.A dozen lines of code can be enough to load your data
|
||
|
|
and create an interactive viewer!
|
||
|
|
</p>
|
||
|
|
|
||
|
|
</p><i>Portability</i> - scene graphs encapsulate much of the lower level tasks of rendering
|
||
|
|
graphics and reading and writing data, reducing or even eradicating the platform specific
|
||
|
|
coding that you require in your own application. If the underlying scene graph is portable
|
||
|
|
then moving from platform to platform can be a simple as recompiling your source code.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
</p><i>Scalability</i> - along with being able to dynamic manage the complexity of scenes
|
||
|
|
automatically to account for differences in graphics performance across a range of machines,
|
||
|
|
scene graphs also make it much easier to manage complex hardware configurations, such as clusters
|
||
|
|
of graphics machines, or multiprocessor/multipipe systems such as SGI's Onyx. A good scene graph
|
||
|
|
will allow the developer to concentrate on developing their own application while rendering
|
||
|
|
framework of the scene graph handles the differnt underlying hardware configurations.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
|
||
|
|
<h2>What the OpenSceneGraph encompasses?</h2>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
|
||
|
|
<h2>How to learn to use the OpenSceneGraph</h2>
|
||
|
|
<hr>
|
||
|
|
|
||
|
|
<h2>Support and discussion - the OpenSceneGraph-news mailing list</h2>
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|