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<title>libQGLViewer cameraLight example</title>
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<h1>The cameraLight example</h1>
<center>
<img src="../images/cameraLight.jpg" width="330" height="228" alt="cameraLight"/>
</center>
<p>
This example shows how to position a GL_LIGHT on the camera.
</p>
<p>
A spot light position and direction are set so that they always match the
camera's current setup.
</p>
<p>
This is done using the <code>camera->position()</code> and <code>camera->viewDirection()</code>
methods which return values expressed in the world coordinates system.
</p>
<h2>cameraLight.h</h2>
<pre>
#include <QGLViewer/qglviewer.h>
class Viewer : public QGLViewer {
protected:
virtual void draw();
virtual void init();
virtual QString helpString() const;
private:
virtual void drawSpiral();
};
</pre>
<h2>cameraLight.cpp</h2>
<pre>
#include "cameraLight.h"
using namespace std;
using namespace qglviewer;
void Viewer::draw() {
// Place light at camera position
const Vec cameraPos = camera()->position();
const GLfloat pos[4] = {(float)cameraPos[0], (float)cameraPos[1],
(float)cameraPos[2], 1.0f};
glLightfv(GL_LIGHT1, GL_POSITION, pos);
// Orientate light along view direction
glLightfv(GL_LIGHT1, GL_SPOT_DIRECTION, camera()->viewDirection());
drawSpiral();
}
// Draws a spiral
void Viewer::drawSpiral() {
const float nbSteps = 1000.0;
glBegin(GL_QUAD_STRIP);
for (int i = 0; i < nbSteps; ++i) {
const float ratio = i / nbSteps;
const float angle = 21.0 * ratio;
const float c = cos(angle);
const float s = sin(angle);
const float r1 = 1.0 - 0.8f * ratio;
const float r2 = 0.8f - 0.8f * ratio;
const float alt = ratio - 0.5f;
const float nor = 0.5f;
const float up = sqrt(1.0 - nor * nor);
glColor3f(1.0 - ratio, 0.2f, ratio);
glNormal3f(nor * c, up, nor * s);
glVertex3f(r1 * c, alt, r1 * s);
glVertex3f(r2 * c, alt + 0.05f, r2 * s);
}
glEnd();
}
void Viewer::init() {
// Light setup
glDisable(GL_LIGHT0);
glEnable(GL_LIGHT1);
// Light default parameters
const GLfloat light_ambient[4] = {1.0, 1.0, 1.0, 1.0};
const GLfloat light_specular[4] = {1.0, 1.0, 1.0, 1.0};
const GLfloat light_diffuse[4] = {1.0, 1.0, 1.0, 1.0};
glLightf(GL_LIGHT1, GL_SPOT_EXPONENT, 3.0);
glLightf(GL_LIGHT1, GL_SPOT_CUTOFF, 10.0);
glLightf(GL_LIGHT1, GL_CONSTANT_ATTENUATION, 0.1f);
glLightf(GL_LIGHT1, GL_LINEAR_ATTENUATION, 0.3f);
glLightf(GL_LIGHT1, GL_QUADRATIC_ATTENUATION, 0.3f);
glLightfv(GL_LIGHT1, GL_AMBIENT, light_ambient);
glLightfv(GL_LIGHT1, GL_SPECULAR, light_specular);
glLightfv(GL_LIGHT1, GL_DIFFUSE, light_diffuse);
// Restore previous viewer state.
restoreStateFromFile();
// Opens help window
help();
}
QString Viewer::helpString() const {
QString text("<h2>C a m e r a L i g h t</h2>");
text += "See the <b>Mouse</b> tab and the documentation web pages for "
"details.<br><br>";
text += "Press <b>Escape</b> to exit the viewer.";
return text;
}
</pre>
<h2>main.cpp</h2>
<pre>
#include "cameraLight.h"
#include <qapplication.h>
int main(int argc, char **argv) {
// Read command lines arguments.
QApplication application(argc, argv);
// Instantiate the viewer.
Viewer viewer;
viewer.setWindowTitle("cameraLight");
// Make the viewer window visible on screen.
viewer.show();
// Run main loop.
return application.exec();
}
</pre>
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