158 lines
5.3 KiB
HTML
158 lines
5.3 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML>
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<HEAD>
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<META http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<TITLE>A Simple Scene Graph API for OpenGL.</TITLE>
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</HEAD>
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<BODY text="#B5A642" link="#8FFF8F" vlink="#18A515" alink="#20336B"
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bgcolor="#005000" background="../marble.png">
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<center>
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<H1>SSG: A Simple Scene Graph API</H1>
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<H1>for OpenGL</H1>
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by Steve Baker
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</center>
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<H2>Introduction</H2>
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Simple Scene Graph (SSG) is intended to be a really simple,
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low-impact, scene graph API that layers nicely on top
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of OpenGL using C++ and which works with or without GLUT.
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<p>
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SSG is a part of <A HREF="../index.html">PLIB</A>.
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<p>
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This document assumes a certain degree of knowledge of
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OpenGL.
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<p>
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SSG includes a subsidiary library of simple matix and vector
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math with support for some intersection testing, field-of-view
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culling and such like. This is called
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<A HREF="../sg/index.html">'Simple Geometry' (SG)</A>.
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SG is used extensively by SSG - but is also useful as a
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standalone library.
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<p>
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A Scene Graph is essentially just a tree-structured database
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containing a hierarchy of branches - and a bunch of leaf nodes.
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Each leaf node does some OpenGL rendering - the branch nodes
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are intended to manage things like: field of view (FOV) culling,
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level of detail (LOD) management, transformations, and animation.
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<p>
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In addition, each leaf node has a structure tacked on to it
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to encapsulate OpenGL state information - and that in turn
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may optionally have a texture applied to it.
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<p>
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In addition to managing the scene graph, SSG contains code
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to manage the positions of cameras, lights and other rendering
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aspects of OpenGL.
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<H2>Symbol Conventions.</H2>
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Both SSG an SG follow conventions for symbols and tokens that
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are the conventions used by OpenGL and GLUT.
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<p>
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Hence, all SSG symbols for classes and functions start with <code>ssg</code>
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and all <code>#define</code> tokens start with <code>SSG</code>. Functions and symbols
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that belong to the SG library similarly start with <code>sg</code> or <code>SG</code>.
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<p>
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Words within a class or function name are Capitalised and NOT
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separated with underscores. Words within <code>#define</code> tokens may
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be separated with underscores to make them readable.
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<H2>Initialisation.</H2>
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The first SSG call in any program must always be ssgInit(). Call
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ssgInit only after you have obtained an OpenGL rendering context
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(or called glutInit() and created a rendering window if you are
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using glut).
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<H2>Classes</H2>
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The following class hierarchy makes up the core package - which
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can be extended to add functionality or to change some underlying
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mechanisms.
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<pre>
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class ssgBase
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|__ class ssgSimpleList
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| |__ class ssgVertexArray
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| |__ class ssgNormalArray
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| |__ class ssgTexCoordArray
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| |__ class ssgColourArray
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| |__ class ssgIndexArray
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|__ class ssgEntity
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| |__ class ssgLeaf
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| | |__ class ssgVTable (deprecated)
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| | |__ class ssgVtxTable
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| | |__ class ssgTween
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| | |__ class ssgVtxArray
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| |__ class ssgBranch
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| |__ class ssgRoot
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| |__ class ssgInvisible
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| |__ class ssgSelector
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| | |__ class ssgTimedSelector
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| | |__ class ssgRangeSelector
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| |__ class ssgBaseTransform
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| | |__ class ssgTransform
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| | |__ class ssgTexTrans
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| |__ class ssgCutout
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| |__ class ssgTweenController
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|___ class ssgState
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| |__ class ssgSimpleState
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| |__ class ssgStateSelector
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|___ class ssgTexture
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</pre>
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The general idea is that, all geometry is contained in ssgLeaf classes,
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all data heirarchy is in a ssgBranch classes and all OpenGL state information
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is in ssgStates.
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<p>
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You may not declare instances of ssgBase, ssgEntity, ssgBaseTransform,
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ssgLeaf or ssgState since they are all abstract classes.
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<p>
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It is presumed that applications will add new kinds of leaves, branches,
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states and textures to customise SSG to their needs.
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<BR><BR>
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Here are the further chapters:
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<BR><BR>
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<A HREF="ssgBase.html">The base class</A>
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<BR>
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<A HREF="ssgEntity.html">An entity of the graph</A>
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<BR>
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<A HREF="ssgLeaf.html">A leaf of the graph</A>
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<BR>
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<A HREF="branches.html">A branch of the graph</A>
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<BR>
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<A HREF="state.html">States (material etc)</A>
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<BR>
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<A HREF="ssgContext.html">ssgContext</A>
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<BR>
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<A HREF="non_class.html">Non-class functions: Loading, saving and optimizing databases</A>
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<BR>
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<A HREF="LoaderWriter.html">How to write plib-loaders and writers</A>
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<BR><BR>
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You can go through all the SSG-documentation by clicking on the "= next =>"-links at the bottom of each page.
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<BR><BR>
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<hr>
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<table width="100%">
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<tr>
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<td width="33%" align="left"></td>
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<td width="34%" align="center"></td>
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<td width="33%" align="right"><a href="ssgBase.html">= next =></a></td>
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</tr>
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</table>
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<hr>
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<table>
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<tr>
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<td>
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<a href="http://validator.w3.org/check/referer"><img border="0" src="../valid-html40.png" alt="Valid HTML 4.0!" height="31" width="88"></a>
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<td>
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<ADDRESS>
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<A HREF="http://www.sjbaker.org">
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Steve J. Baker.</A>
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<<A HREF="mailto:sjbaker1@airmail.net">sjbaker1@airmail.net</A>>
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</ADDRESS>
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</table>
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</BODY>
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</HTML>
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