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<title>libQGLViewer clippingPlane example</title>
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<h1>The clippingPlane example</h1>
<center>
<img src="../images/clippingPlane.jpg" width="330" height="228" alt="clippingPlane"/>
</center>
<p>
A clipping plane is manipulated using a ManipulatedFrame
</p>
<p>
The standard OpenGL <i>GL_CLIP_PLANE</i> feature is used to add an additionnal clipping
plane in the scene, which position and orientation are set by a <b>ManipulatedFrame</b>.
</p>
<p>
Hold the <b>Control</b> key pressed down while using the mouse to modify the plane orientation (left button)
and position (right button) and to interactively see the clipped result.
</p>
<p>
Since the plane equation is defined with respect to the current modelView matrix, a constant equation (normal
along the Z axis) can be used since we transformed the coordinates system using the <b>matrix()</b> method.
</p>
<h2>clippingPlane.h</h2>
<pre>
#include <QGLViewer/qglviewer.h>
class Viewer : public QGLViewer {
protected:
virtual void draw();
virtual void init();
virtual QString helpString() const;
};
</pre>
<h2>clippingPlane.cpp</h2>
<pre>
#include "clippingPlane.h"
#include "QGLViewer/manipulatedFrame.h"
using namespace std;
using namespace qglviewer;
// Draws a spiral
void Viewer::draw() {
const float nbSteps = 200.0;
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();
glPushMatrix();
glMultMatrixd(manipulatedFrame()->matrix());
// Since the Clipping Plane equation is multiplied by the current modelView,
// we can define a constant equation (plane normal along Z and passing by the
// origin) since we are here in the manipulatedFrame coordinates system (we
// glMultMatrixd() with the manipulatedFrame matrix()).
static const GLdouble equation[] = {0.0, 0.0, 1.0, 0.0};
glClipPlane(GL_CLIP_PLANE0, equation);
// Draw a plane representation: Its normal...
glColor3f(0.8f, 0.8f, 0.8f);
drawArrow(0.4f, 0.015f);
// ...and a quad (with a slightly shifted z so that it is not clipped).
glBegin(GL_QUADS);
glVertex3f(-1.0, -1.0, 0.001f);
glVertex3f(-1.0, 1.0, 0.001f);
glVertex3f(1.0, 1.0, 0.001f);
glVertex3f(1.0, -1.0, 0.001f);
glEnd();
glPopMatrix();
}
void Viewer::init() {
// Restore previous viewer state.
restoreStateFromFile();
// Opens help window
help();
// The ManipulatedFrame will be used to position the clipping plane
setManipulatedFrame(new ManipulatedFrame());
// Enable plane clipping
glEnable(GL_CLIP_PLANE0);
}
QString Viewer::helpString() const {
QString text("<h2>C l i p p i n g P l a n e</h2>");
text += "The standard OpenGL <i>GL_CLIP_PLANE</i> feature is used to add an "
"additionnal clipping ";
text += "plane in the scene, which position and orientation are set by a "
"<b>ManipulatedFrame</b>.<br><br>";
text += "Hold the <b>Control</b> key pressed down while using the mouse to "
"modify the plane orientation (left button) ";
text += "and position (right button) and to interactively see the clipped "
"result.<br><br>";
text += "Since the plane equation is defined with respect to the current "
"modelView matrix, a constant equation (normal";
text += "along the Z axis) can be used since we transformed the coordinates "
"system using the <b>matrix()</b> method.";
return text;
}
</pre>
<h2>main.cpp</h2>
<pre>
#include "clippingPlane.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("clippingPlane");
// Make the viewer window visible on screen.
viewer.show();
// Run main loop.
return application.exec();
}
</pre>
<p>
Back to the <a href="index.html">examples main page</a>.
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