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<title>libQGLViewer frameTransform example</title>
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</div>
<h1>The frameTransform example</h1>
<center>
<img src="../images/frameTransform.jpg" width="330" height="228" alt="frameTransform"/>
</center>
<p>
Coordinate transformation between different Frames.
</p>
<p>
This example illustrates the camera and world coordinate systems relationship. The position of the
camera in the world coordinate system is printed from <code>camera()->position()</code>.
Symmetrically, the position of the world origin is given in the camera coordinate system by
<code>camera()->cameraCoordinatesOf(0,0,0)</code>.
</p>
<p>
Three sets of lines (red, green, blue) are drawn. They have different starting points, but common
end points, located on a circle in the XY plane.
</p>
<p>
All the red lines start from the camera position, and will hence always be aligned with the
viewing direction, making them invisible.
</p>
<p>
The green lines starting points' positions are determined from the camera coordinate system, using
<code>camera()->worldCoordinatesOf()</code>. As a result, these points will seem to be fixed on
the screen, even when the camera is moved
</p>
<p>
Finally, the blue lines are classically defined in the world coordinate system, and will move with
the camera.
</p>
<p>
Beautiful Moire pattern can be obtained with a proper rotation.
</p>
<h2>frameTransform.h</h2>
<pre>
#include <QGLViewer/qglviewer.h>
class Viewer : public QGLViewer {
protected:
virtual void draw();
virtual void init();
virtual QString helpString() const;
};
</pre>
<h2>frameTransform.cpp</h2>
<pre>
#include "frameTransform.h"
using namespace std;
using namespace qglviewer; // Vec
void Viewer::init() {
restoreStateFromFile();
setSceneRadius(1.5);
showEntireScene();
setAxisIsDrawn();
glDisable(GL_LIGHTING);
help();
}
void Viewer::draw() {
// Draws line sets (red, green, blue) with different origins, but with a
// common end point, located on a circle in the XY plane.
const float nbLines = 50.0;
glBegin(GL_LINES);
for (float i = 0; i < nbLines; ++i) {
float angle = 2.0 * M_PI * i / nbLines;
glColor3f(0.8f, 0.2f, 0.2f);
// These lines will never be seen as they are always aligned with the
// viewing direction.
glVertex3fv(camera()->position());
glVertex3f(cos(angle), sin(angle), 0.0);
glColor3f(0.2f, 0.8f, 0.2f);
// World Coordinates are infered from the camera, and seem to be immobile in
// the screen.
glVertex3fv(camera()->worldCoordinatesOf(
Vec(.3 * cos(angle), .3 * sin(angle), -2.0)));
glVertex3f(cos(angle), sin(angle), 0.0);
glColor3f(0.2f, 0.2f, 0.8f);
// These lines are defined in the world coordinate system and will move with
// the camera.
glVertex3f(1.5 * cos(angle), 1.5 * sin(angle), -1.0);
glVertex3f(cos(angle), sin(angle), 0.0);
}
glEnd();
// Here, the camera position in world coord. system is camera()->position().
// The world origin position in camera frame can be obtained from
// camera()->cameraCoordinatesOf(Vec(0.0, 0.0, 0.0))
}
QString Viewer::helpString() const {
QString text("<h2>F r a m e T r a n s f o r m</h2>");
text += "This example illustrates how easy it is to switch between the "
"camera and ";
text += "the world coordinate systems using the "
"<i>camera()->cameraCoordinatesOf()</i> ";
text += "and <i>camera::worldCoordinatesOf()</i> functions.<br><br>";
text += "You can create your own hierarchy of local coordinates systems and "
"each of ";
text += "them can be manipulated with the mouse (see the "
"<i>manipulatedFrame</i> and <i>luxo</i> examples). ";
text += "Standard functions allow you to convert from any local frame to any "
"other, ";
text += "the world/camera conversion presented here simply being an "
"illustration.<br><br>";
text += "See <i>examples/frameTransform.html</i> for an explanation of the "
"meaning of these weird lines.";
return text;
}
</pre>
<h2>main.cpp</h2>
<pre>
#include "frameTransform.h"
#include <qapplication.h>
int main(int argc, char **argv) {
QApplication application(argc, argv);
Viewer viewer;
viewer.setWindowTitle("frameTransform");
viewer.show();
return application.exec();
}
</pre>
<p>
Back to the <a href="index.html">examples main page</a>.
</p>
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