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<h1>The constrainedCamera example</h1>

<center>
  <img src="../images/constrainedCamera.jpg" width="330" height="228" alt="constrainedCamera"/>
</center>

<p>
 Constraints applied on the Camera Frame to limit its translation and/or rotation.
</p>
<p>
 Try the different possible constraints using the T (translate) and R (rotate) keys. G and D change
 the constraint directions. Press Space to change the coordinate system (World or Camera) which
 defines the constraint directions.
</p>
<p>
 Note that in order to apply a constraint to a camera, you need to apply it to the camera()-&gt;frame().
</p>
<h2>constrainedCamera.h</h2>
<pre>
#include &lt;QGLViewer/qglviewer.h&gt;

class Viewer : public QGLViewer {
protected:
  virtual void init();
  virtual void draw();
  virtual QString helpString() const;
  virtual void keyPressEvent(QKeyEvent *);

  void displayText();
  void displayType(const qglviewer::AxisPlaneConstraint::Type type, const int x,
                   const int y, const char c);
  void displayDir(const unsigned short dir, const int x, const int y,
                  const char c);

private:
  int transDir;
  int rotDir;

  static qglviewer::AxisPlaneConstraint::Type nextTranslationConstraintType(
      const qglviewer::AxisPlaneConstraint::Type &amp;type);
  static qglviewer::AxisPlaneConstraint::Type
  nextRotationConstraintType(const qglviewer::AxisPlaneConstraint::Type &amp;type);

  void changeConstraint();
  qglviewer::AxisPlaneConstraint *constraints[2];
  unsigned short activeConstraint;
};
</pre>


<h2>constrainedCamera.cpp</h2>
<pre>
#include "constrainedCamera.h"

#include &lt;QGLViewer/manipulatedCameraFrame.h&gt;
#include &lt;QKeyEvent&gt;

using namespace qglviewer;
using namespace std;

AxisPlaneConstraint::Type
Viewer::nextTranslationConstraintType(const AxisPlaneConstraint::Type &amp;type) {
  switch (type) {
  case AxisPlaneConstraint::FREE:
    return AxisPlaneConstraint::PLANE;
    break;
  case AxisPlaneConstraint::PLANE:
    return AxisPlaneConstraint::AXIS;
    break;
  case AxisPlaneConstraint::AXIS:
    return AxisPlaneConstraint::FORBIDDEN;
    break;
  case AxisPlaneConstraint::FORBIDDEN:
    return AxisPlaneConstraint::FREE;
    break;
  default:
    return AxisPlaneConstraint::FREE;
  }
}

AxisPlaneConstraint::Type
Viewer::nextRotationConstraintType(const AxisPlaneConstraint::Type &amp;type) {
  switch (type) {
  case AxisPlaneConstraint::FREE:
    return AxisPlaneConstraint::AXIS;
    break;
  case AxisPlaneConstraint::PLANE:
    return AxisPlaneConstraint::FREE;
    break;
  case AxisPlaneConstraint::AXIS:
    return AxisPlaneConstraint::FORBIDDEN;
    break;
  case AxisPlaneConstraint::FORBIDDEN:
    return AxisPlaneConstraint::FREE;
    break;
  default:
    return AxisPlaneConstraint::FREE;
  }
}

void Viewer::changeConstraint() {
  unsigned short previous = activeConstraint;
  activeConstraint = (activeConstraint + 1) % 2;

  constraints[activeConstraint]-&gt;setTranslationConstraintType(
      constraints[previous]-&gt;translationConstraintType());
  constraints[activeConstraint]-&gt;setTranslationConstraintDirection(
      constraints[previous]-&gt;translationConstraintDirection());
  constraints[activeConstraint]-&gt;setRotationConstraintType(
      constraints[previous]-&gt;rotationConstraintType());
  constraints[activeConstraint]-&gt;setRotationConstraintDirection(
      constraints[previous]-&gt;rotationConstraintDirection());

  camera()-&gt;frame()-&gt;setConstraint(constraints[activeConstraint]);
}

void Viewer::init() {
  restoreStateFromFile();

  constraints[0] = new WorldConstraint();

  // Note that a CameraConstraint(camera) would produce the same results:
  // A CameraConstraint is a LocalConstraint when applied to the camera frame !
  constraints[1] = new LocalConstraint();

  transDir = 0;
  rotDir = 0;
  activeConstraint = 0;

  camera()-&gt;frame()-&gt;setConstraint(constraints[activeConstraint]);

  setAxisIsDrawn();

  setKeyDescription(Qt::Key_G, "Change translation constraint direction");
  setKeyDescription(Qt::Key_D, "Change rotation constraint direction");
  setKeyDescription(Qt::Key_Space, "Change constraint reference");
  setKeyDescription(Qt::Key_T, "Change translation constraint type");
  setKeyDescription(Qt::Key_R, "Change rotation constraint type");

  help();
}

void Viewer::draw() {
  const float nbSteps = 200.0;
  glBegin(GL_QUAD_STRIP);
  for (float i = 0; i &lt; nbSteps; ++i) {
    float ratio = i / nbSteps;
    float angle = 21.0 * ratio;
    float c = cos(angle);
    float s = sin(angle);
    float r1 = 1.0 - 0.8 * ratio;
    float r2 = 0.8 - 0.8 * ratio;
    float alt = ratio - 0.5;
    const float nor = .5;
    const float up = sqrt(1.0 - nor * nor);
    glColor3f(1 - ratio, 0.2f, ratio);
    glNormal3f(nor * c, up, nor * s);
    glVertex3f(r1 * c, alt, r1 * s);
    glVertex3f(r2 * c, alt + 0.05, r2 * s);
  }
  glEnd();

  displayText();
}

void Viewer::keyPressEvent(QKeyEvent *e) {
  switch (e-&gt;key()) {
  case Qt::Key_G:
    transDir = (transDir + 1) % 3;
    break;
  case Qt::Key_D:
    rotDir = (rotDir + 1) % 3;
    break;
  case Qt::Key_Space:
    changeConstraint();
    break;
  case Qt::Key_T:
    constraints[activeConstraint]-&gt;setTranslationConstraintType(
        nextTranslationConstraintType(
            constraints[activeConstraint]-&gt;translationConstraintType()));
    break;
  case Qt::Key_R:
    constraints[activeConstraint]-&gt;setRotationConstraintType(
        nextRotationConstraintType(
            constraints[activeConstraint]-&gt;rotationConstraintType()));
    break;
  default:
    QGLViewer::keyPressEvent(e);
  }

  Vec dir(0.0, 0.0, 0.0);
  dir[transDir] = 1.0;
  constraints[activeConstraint]-&gt;setTranslationConstraintDirection(dir);

  dir = Vec(0.0, 0.0, 0.0);
  dir[rotDir] = 1.0;
  constraints[activeConstraint]-&gt;setRotationConstraintDirection(dir);

  update();
}

void Viewer::displayType(const AxisPlaneConstraint::Type type, const int x,
                         const int y, const char c) {
  QString text;
  switch (type) {
  case AxisPlaneConstraint::FREE:
    text = QString("FREE (%1)").arg(c);
    break;
  case AxisPlaneConstraint::PLANE:
    text = QString("PLANE (%1)").arg(c);
    break;
  case AxisPlaneConstraint::AXIS:
    text = QString("AXIS (%1)").arg(c);
    break;
  case AxisPlaneConstraint::FORBIDDEN:
    text = QString("FORBIDDEN (%1)").arg(c);
    break;
  }
  drawText(x, y, text);
}

void Viewer::displayDir(const unsigned short dir, const int x, const int y,
                        const char c) {
  QString text;
  switch (dir) {
  case 0:
    text = QString("X (%1)").arg(c);
    break;
  case 1:
    text = QString("Y (%1)").arg(c);
    break;
  case 2:
    text = QString("Z (%1)").arg(c);
    break;
  }
  drawText(x, y, text);
}

void Viewer::displayText() {
  glColor4f(foregroundColor().redF(), foregroundColor().greenF(),
            foregroundColor().blueF(), foregroundColor().alphaF());
  glDisable(GL_LIGHTING);
  drawText(10, height() - 30, "TRANSLATION :");
  displayDir(transDir, 190, height() - 30, 'G');
  displayType(constraints[activeConstraint]-&gt;translationConstraintType(), 10,
              height() - 60, 'T');

  drawText(width() - 220, height() - 30, "ROTATION :");
  displayDir(rotDir, width() - 100, height() - 30, 'D');
  displayType(constraints[activeConstraint]-&gt;rotationConstraintType(),
              width() - 220, height() - 60, 'R');

  switch (activeConstraint) {
  case 0:
    drawText(20, 20, "Constraint direction defined w/r to WORLD (SPACE)");
    break;
  case 1:
    drawText(20, 20, "Constraint direction defined w/r to CAMERA (SPACE)");
    break;
  }

  glEnable(GL_LIGHTING);
}

QString Viewer::helpString() const {
  QString text("&lt;h2&gt;C o n s t r a i n e d C a m e r a&lt;/h2&gt;");
  text += "The camera frame can be constrained to limit the camera "
          "displacements.&lt;br&gt;&lt;br&gt;";
  text += "Try the different translation (press &lt;b&gt;G&lt;/b&gt; and &lt;b&gt;T&lt;/b&gt;) and "
          "rotation ";
  text += "(&lt;b&gt;D&lt;/b&gt; and &lt;b&gt;R&lt;/b&gt;) constraints while moving the camera with "
          "the mouse. ";
  text += "The constraints can be defined with respect to various coordinates ";
  text += "systems : press &lt;b&gt;Space&lt;/b&gt; to switch.&lt;br&gt;&lt;br&gt;";
  text += "You can easily define your own constraints to create a specific "
          "camera constraint.";
  return text;
}
</pre>


<h2>main.cpp</h2>
<pre>
#include "constrainedCamera.h"
#include &lt;qapplication.h&gt;

int main(int argc, char **argv) {
  QApplication application(argc, argv);

  Viewer viewer;

  viewer.setWindowTitle("constrainedCamera");

  viewer.show();

  return application.exec();
}
</pre>



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