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<title>libQGLViewer drawLight example</title>
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<h1>The drawLight example</h1>
<center>
<img src="../images/drawLight.jpg" width="300" height="200" alt="drawLight"/>
</center>
<p>
The <code>drawLight()</code> function is a light debugging tool.
</p>
<p>
drawLight() takes as an argument the GL index of the lamp : GL_LIGHT0, GL_LIGHT1... and displays a
symbolic representation of the light. This function is usefull for debugging your light setup.
</p>
<h2>drawLight.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>draw();
<span class="key">virtual </span><span class="typ">void </span>init();
<span class="key">virtual </span>QString helpString() <span class="typ">const</span>;
};</pre>
<h2>drawLight.cpp</h2>
<pre>
<span class="dir">#include </span><span class="dstr">"drawLight.h"</span><span class="dir">
</span><span class="dir">#include <math.h>
</span>
<span class="key">using namespace </span>std;
<span class="typ">void </span>Viewer::draw()
{
<span class="typ">const float </span>nbSteps = <span class="num">500.0</span>;
glBegin(GL_QUAD_STRIP);
<span class="key">for </span>(<span class="typ">float </span>i=<span class="num">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>c = cos(angle);
<span class="typ">float </span>s = sin(angle);
<span class="typ">float </span>r1 = <span class="num">1.0 </span>- <span class="num">0.8</span>*ratio;
<span class="typ">float </span>r2 = <span class="num">0.8 </span>- <span class="num">0.8</span>*ratio;
<span class="typ">float </span>alt = ratio <span class="num">- 0.5</span>;
<span class="typ">const float </span>nor = .<span class="num">5</span>;
<span class="typ">const float </span>up = sqrt(<span class="num">1.0</span>-nor*nor);
glColor3f(<span class="num">1</span>-ratio, .<span class="num">2 </span>, ratio);
glNormal3f(nor*c, up, nor*s);
glVertex3f(r1*c, alt, r1*s);
glVertex3f(r2*c, alt+<span class="num">0.05</span>, r2*s);
}
glEnd();
drawLight(GL_LIGHT0);
<span class="typ">const </span>GLfloat pos1[<span class="num">4</span>] = {<span class="num">0.5</span>,<span class="num">0.5</span>,<span class="num">0.0</span>,<span class="num">1.0</span>};
<span class="typ">const </span>GLfloat spot_dir1[<span class="num">3</span>] = {<span class="num">-1.0</span>, <span class="num">-1.0</span>, <span class="num">0.0</span>};
glLightfv(GL_LIGHT1, GL_POSITION, pos1);
glLightfv(GL_LIGHT1, GL_SPOT_DIRECTION, spot_dir1);
drawLight(GL_LIGHT1, <span class="num">2.0</span>); <span class="com">// Draw this light twice bigger
</span>
<span class="typ">const </span>GLfloat pos2[<span class="num">4</span>] = {<span class="num">-0.5</span>,<span class="num">0.5</span>,<span class="num">0.0</span>,<span class="num">1.0</span>};
<span class="typ">const </span>GLfloat spot_dir2[<span class="num">3</span>] = {<span class="num">1.0</span>, <span class="num">1.0</span>, <span class="num">1.0</span>};
glLightfv(GL_LIGHT2, GL_POSITION, pos2);
glLightfv(GL_LIGHT2, GL_SPOT_DIRECTION, spot_dir2);
drawLight(GL_LIGHT2);
}
<span class="typ">void </span>Viewer::init()
{
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
<span class="com">// Light0 is the default ambient light
</span> glEnable(GL_LIGHT0);
<span class="com">// Light1 is a spot light
</span> glEnable(GL_LIGHT1);
<span class="typ">const </span>GLfloat light_ambient[<span class="num">4</span>] = {<span class="num">0.5</span>, <span class="num">0.5</span>, <span class="num">0.5</span>, <span class="num">1.0</span>};
<span class="typ">const </span>GLfloat light_specular[<span class="num">4</span>] = {<span class="num">1.0</span>, <span class="num">1.0</span>, <span class="num">1.0</span>, <span class="num">1.0</span>};
<span class="typ">const </span>GLfloat light_diffuse[<span class="num">4</span>] = {<span class="num">3.0</span>, <span class="num">3.0</span>, <span class="num">1.0</span>, <span class="num">1.0</span>};
glLightf( GL_LIGHT1, GL_SPOT_EXPONENT, <span class="num">3.0</span>);
glLightf( GL_LIGHT1, GL_SPOT_CUTOFF, <span class="num">50.0</span>);
glLightf( GL_LIGHT1, GL_CONSTANT_ATTENUATION, <span class="num">0.5</span>);
glLightf( GL_LIGHT1, GL_LINEAR_ATTENUATION, <span class="num">1.0</span>);
glLightf( GL_LIGHT1, GL_QUADRATIC_ATTENUATION, <span class="num">1.5</span>);
glLightfv(GL_LIGHT1, GL_AMBIENT, light_ambient);
glLightfv(GL_LIGHT1, GL_SPECULAR, light_specular);
glLightfv(GL_LIGHT1, GL_DIFFUSE, light_diffuse);
<span class="com">// Light2 is a classical directionnal light
</span> glEnable(GL_LIGHT2);
<span class="typ">const </span>GLfloat light_ambient2[<span class="num">4</span>] = {<span class="num">0.5</span>, <span class="num">0.5</span>, <span class="num">0.5</span>, <span class="num">1.0</span>};
<span class="typ">const </span>GLfloat light_specular2[<span class="num">4</span>] = {<span class="num">1.0</span>, <span class="num">0.0</span>, <span class="num">0.0</span>, <span class="num">1.0</span>};
<span class="typ">const </span>GLfloat light_diffuse2[<span class="num">4</span>] = {<span class="num">0.0</span>, <span class="num">3.0</span>, <span class="num">0.0</span>, <span class="num">1.0</span>};
glLightfv(GL_LIGHT2, GL_AMBIENT, light_ambient2);
glLightfv(GL_LIGHT2, GL_SPECULAR, light_specular2);
glLightfv(GL_LIGHT2, GL_DIFFUSE, light_diffuse2);
restoreFromFile();
help();
}
QString Viewer::helpString() <span class="typ">const
</span>{
QString text(<span class="str">"<h2>D r a w L i g h t</h2>"</span>);
text += <span class="str">"The <i>drawLight()</i> function displays a representation of the OpenGL lights "</span>;
text += <span class="str">"of your scene. This is convenient for debugging your light setup."</span>;
<span class="key">return </span>text;
}</pre>
<h2>main.cpp</h2>
<pre>
<span class="dir">#include </span><span class="dstr">"drawLight.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 viewer;
<span class="com">// Make the viewer window visible on screen.
</span> viewer.show();
<span class="com">// Set the viewer as the application main widget.
</span> application.setMainWidget(&viewer);
<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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