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<title>libQGLViewer fastDraw example</title>
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<h1>The fastDraw example</h1>
<center>
<img src="../images/fastDraw.jpg" width="300" height="200" alt="fastDraw"/>
</center>
<p>
The <code>fastDraw()</code> function keeps interactivity even with large scenes.
</p>
<p>
This example demonstrates the use of the <code>fastDraw()</code> function, which
is called when the camera moves. This function is usefull for displaying very
complex scene, while keeping an interactive camera motion.
</p>
<h2>fastDraw.h</h2>
<pre>
<span class="dir">#include <QGLViewer/qglviewer.h>
</span>
<span class="key">class </span>Viewer : <span class="key">public </span>QGLViewer
{
<span class="key">protected</span>:
<span class="key">virtual </span><span class="typ">void </span>init();
<span class="key">virtual </span><span class="typ">void </span>draw();
<span class="key">virtual </span><span class="typ">void </span>fastDraw();
<span class="key">virtual </span>QString helpString() <span class="typ">const</span>;
};</pre>
<h2>fastDraw.cpp</h2>
<pre>
<span class="dir">#include </span><span class="dstr">"fastDraw.h"</span><span class="dir">
</span>
<span class="key">using namespace </span>std;
<span class="key">using namespace </span>qglviewer;
<span class="typ">void </span>Viewer::init()
{
<span class="com">// Increase the material shininess, so that the difference between
</span> <span class="com">// the two versions of the spiral is more visible.
</span> glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, <span class="num">50.0</span>);
GLfloat specular_color[<span class="num">4</span>] = { <span class="num">0.8</span>, <span class="num">0.8</span>, <span class="num">0.8</span>, <span class="num">1.0 </span>};
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, specular_color);
restoreFromFile();
help();
}
<span class="typ">static void </span>drawSpiral(<span class="typ">bool </span>simplified = <span class="key">false</span>)
{
<span class="typ">int </span>nbSteps = <span class="num">600</span>;
<span class="typ">int </span>nbSub = <span class="num">50</span>;
<span class="key">if </span>(simplified)
{
nbSteps = <span class="num">60</span>;
nbSub = <span class="num">2</span>;
}
<span class="key">for </span>(<span class="typ">float </span>n=<span class="num">0</span>; n<nbSub; ++n)
{
glBegin(GL_QUAD_STRIP);
<span class="key">for </span>(<span class="typ">float </span>i=<span class="num">0.0</span>; i<nbSteps; ++i)
{
<span class="typ">float </span>ratio = i/nbSteps;
<span class="typ">float </span>angle = <span class="num">21.0</span>*ratio;
<span class="typ">float </span>radius = <span class="num">1.0 </span>- <span class="num">0.5</span>*ratio;
Vec center(radius*cos(angle), ratio-0.<span class="num">5</span>, radius*sin(angle));
<span class="key">for </span>(<span class="typ">unsigned short </span>j=<span class="num">0</span>; j<<span class="num">2</span>; ++j)
{
<span class="typ">float </span>delta = <span class="num">3.0</span>*(n+j)/nbSub;
Vec shift(cos(angle)*cos(delta), sin(delta), sin(angle)*cos(delta));
glColor3f(<span class="num">1</span>-ratio, (n+j)/nbSub , ratio);
glNormal3fv(shift.address());
glVertex3fv((center+<span class="num">0.2</span>*shift).address());
}
}
glEnd();
}
}
<span class="typ">void </span>Viewer::draw()
{
drawSpiral();
}
<span class="typ">void </span>Viewer::fastDraw()
{
drawSpiral(<span class="key">true</span>);
}
QString Viewer::helpString() <span class="typ">const
</span>{
QString text(<span class="str">"<h2>F a s t D r a w</h2>"</span>);
text += <span class="str">"The <i>fastDraw()</i> function is called instead of <i>draw()</i> when the camera is manipulated, "</span>;
text += <span class="str">"thus allowing interactive displacements even with very complex scenes, as soon as you provide a fast drawing function."</span>;
<span class="key">return </span>text;
}</pre>
<h2>main.cpp</h2>
<pre>
<span class="dir">#include </span><span class="dstr">"fastDraw.h"</span><span class="dir">
</span><span class="dir">#include <qapplication.h>
</span>
<span class="typ">int </span>main(<span class="typ">int </span>argc, <span class="typ">char</span>** argv)
{
<span class="com">// Read command lines arguments.
</span> QApplication application(argc,argv);
<span class="com">// Instantiate the viewer.
</span> Viewer v;
<span class="com">// Make the viewer window visible on screen.
</span> v.show();
<span class="com">// Set the viewer as the application main widget.
</span> application.setMainWidget(&v);
<span class="com">// Run main loop.
</span> <span class="key">return </span>application.exec();
}</pre>
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<i>Last modified on Thursday, February 5, 2004.</i>
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