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<h1>QGLViewer - Introduction</h1>
<h2>Philosophy</h2>
QGLViewer provides 3D application developers some of the classical features of a 3D viewer. See the
<a href="features.html">feature list</a> for details. All the functionalities of the viewer are
illustrated by a very simple example which can be used as a cut and paste source for your own
applications.
<p>
QGLViewer enables you to quickly develop a small test program as well as a complete 3D application.
It is versatile and is not designed for any specific application. It it also very convenient as a
3D/openGL pedagogical tool.
</p>
<h2>The QGLViewer class</h2>
You will use the library by deriving a viewer class from the <code>QGLViewer</code> main class. All you
need to do is to overload the <code>draw()</code> function, which will contain the OpenGL orders that describe
your 3D scene. You may want to read a very simple <a href="commented.html">commented program</a> to
see exactly how it works.
<br/>
The different classical functionalities of a 3D viewer are provided by the <code>QGLViewer</code>
class, and can be overloaded in your own application. Apart from the <code>draw()</code> function, an
other good example is the <code>init()</code> function, which can be used to initialize the openGL state
of your viewer, before the first display. Many other functions can be used as is or redefined, see
the <a href="features.html">feature list</a> for a complete description of the available functions.
<h2>Camera and world coordinate system</h2>
When you start giving openGL orders in your <code>draw()</code> function, you are implicitly located at
the origin of the so-called <i>world coordinate system</i>. The camera is an "object" located in
this virtual world, that can be moved with the mouse (try to press 'A', the drawAxis() shortcut key
to see the world coordinate system). This conception is different (but much more intuitive) than the
original camera-centered openGL coordinate system.
<h2>Scene radius and center</h2>
<code>QGLViewer</code> is versatile and makes no assumptions on the type of 3D application you are
developing. However, in order to implement <code>camera()->showEntireScene()</code>, to set the fly speed in
walkthrough mode, to optimally set the <code>ZNear</code> and <code>ZFar</code> of the camera or to tune the
stereo display, you need to provide an approximation of your <i>Scene radius</i>, expressed in
openGL units. This is done using the <code>setSceneRadius()</code> function.
<br/>
You may also want to tune the <i>Scene center</i> if your scene is not centered on the
world coordinate origin (0,0,0).
<br/><br/>
Default scene radius is 1.0 and the scene center is located at the world origin. If your viewer
remains desperately black, try to use code like this in your <code>init()</code> function:
<pre>
<font color="#2040a0">setSceneRadius</font><font color="4444FF">(</font><font color="#FF0000">100.0</font><font color="4444FF">)</font><font color="4444FF">;</font> <font color="#444444">// for instance </font>
<font color="#2040a0">setSceneCenter</font><font color="4444FF">(</font><font color="#FF0000">400</font>,<font color="#FF0000">0</font>,<font color="#FF0000">0</font><font color="4444FF">)</font><font color="4444FF">;</font> <font color="#444444">// for instance</font>
<font color="#2040a0">camera</font>.<font color="#2040a0">showEntireScene</font><font color="4444FF">(</font><font color="4444FF">)</font><font color="4444FF">;</font>
</pre>
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<i>Last modified on Tuesday, October 21, 2003.</i>
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