The constrainedCamera example

constrainedCamera

Constraints applied on the Camera Frame to limit its translation and/or rotation.

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.

Note that in order to apply a constraint to a camera, you need to apply it to the camera()->frame().

constrainedCamera.h

#include <QGLViewer/qglviewer.h>

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

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

constrainedCamera.cpp

#include "constrainedCamera.h"

#include <QKeyEvent>
#include <QGLViewer/manipulatedCameraFrame.h>

using namespace qglviewer;
using namespace std;

AxisPlaneConstraint::Type Viewer::nextTranslationConstraintType(const AxisPlaneConstraint::Type& 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& 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]->setTranslationConstraintType(constraints[previous]->translationConstraintType());
  constraints[activeConstraint]->setTranslationConstraintDirection(constraints[previous]->translationConstraintDirection());
  constraints[activeConstraint]->setRotationConstraintType(constraints[previous]->rotationConstraintType());
  constraints[activeConstraint]->setRotationConstraintDirection(constraints[previous]->rotationConstraintDirection());

  camera()->frame()->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()->frame()->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<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->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]->setTranslationConstraintType(nextTranslationConstraintType(constraints[activeConstraint]->translationConstraintType()));
	  break;
	case Qt::Key_R :
	  constraints[activeConstraint]->setRotationConstraintType(nextRotationConstraintType(constraints[activeConstraint]->rotationConstraintType()));
	  break;
	default:
	  QGLViewer::keyPressEvent(e);
	}

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

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

  updateGL();
}

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()
{
  qglColor(foregroundColor());
  glDisable(GL_LIGHTING);
  drawText(10,height()-30, "TRANSLATION :");
  displayDir(transDir, 190, height()-30, 'G');
  displayType(constraints[activeConstraint]->translationConstraintType(), 10, height()-60, 'T');

  drawText(width()-220,height()-30, "ROTATION :");
  displayDir(rotDir, width()-100, height()-30, 'D');
  displayType(constraints[activeConstraint]->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("<h2>C o n s t r a i n e d C a m e r a</h2>");
  text += "The camera frame can be constrained to limit the camera displacements.<br><br>";
  text += "Try the different translation (press <b>G</b> and <b>T</b>) and rotation ";
  text += "(<b>D</b> and <b>R</b>) constraints while moving the camera with the mouse. ";
  text += "The constraints can be defined with respect to various coordinates ";
  text += "systems : press <b>Space</b> to switch.<br><br>";
  text += "You can easily define your own constraints to create a specific camera constraint.";
  return text;
}

main.cpp

#include "constrainedCamera.h"
#include <qapplication.h>

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

  Viewer viewer;

  viewer.setWindowTitle("constrainedCamera");

  viewer.show();

  return application.exec();
}

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