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<h1>The fastDraw example</h1>
<center>
<img src="../images/fastDraw.jpg" width="330" height="228" alt="fastDraw"/>
</center>
<p>
The <code>fastDraw()</code> function enables interactivity even with large scenes.
</p>
<p>
This example demonstrates the use of the <code>fastDraw()</code> function, which
is called when the camera is manipulated. This function can be used to display a
simplified version of the scene and is usefull for displaying very complex scene,
while keeping an interactive camera motion.
</p>
<h2>fastDraw.h</h2>
<pre>
#include <QGLViewer/qglviewer.h>
class Viewer : public QGLViewer {
protected:
virtual void init();
virtual void draw();
virtual void fastDraw();
virtual QString helpString() const;
};
</pre>
<h2>fastDraw.cpp</h2>
<pre>
#include "fastDraw.h"
using namespace std;
using namespace qglviewer;
void Viewer::init() {
// Increase the material shininess, so that the difference between
// the two versions of the spiral is more visible.
glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, 50.0);
GLfloat specular_color[4] = {0.8f, 0.8f, 0.8f, 1.0};
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, specular_color);
restoreStateFromFile();
help();
}
static void drawSpiral(bool simplified = false) {
int nbSteps = 600;
int nbSub = 50;
if (simplified) {
nbSteps = 60;
nbSub = 2;
}
for (float n = 0; n < nbSub; ++n) {
glBegin(GL_QUAD_STRIP);
for (float i = 0.0; i < nbSteps; ++i) {
float ratio = i / nbSteps;
float angle = 21.0 * ratio;
float radius = 1.0 - 0.5 * ratio;
Vec center(radius * cos(angle), ratio - 0.5, radius * sin(angle));
for (unsigned short j = 0; j < 2; ++j) {
float delta = 3.0 * (n + j) / nbSub;
Vec shift(cos(angle) * cos(delta), sin(delta), sin(angle) * cos(delta));
glColor3f(1 - ratio, (n + j) / nbSub, ratio);
glNormal3fv(shift);
glVertex3fv(center + 0.2f * shift);
}
}
glEnd();
}
}
void Viewer::draw() { drawSpiral(); }
void Viewer::fastDraw() { drawSpiral(true); }
QString Viewer::helpString() const {
QString text("<h2>F a s t D r a w</h2>");
text += "The <code>fastDraw()</code> function is called instead of "
"<code>draw()</code> when the camera ";
text += "is manipulated. Providing such a simplified version of "
"<code>draw()</code> allows for interactive ";
text += "frame rates when the camera is moved, even for very complex scenes.";
return text;
}
</pre>
<h2>main.cpp</h2>
<pre>
#include "fastDraw.h"
#include <qapplication.h>
int main(int argc, char **argv) {
QApplication application(argc, argv);
Viewer viewer;
viewer.setWindowTitle("fastDraw");
viewer.show();
return application.exec();
}
</pre>
<p>
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