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# The constrainedCamera example

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"

    #if QT_VERSION >= 0x040000
    # include <QKeyEvent>
    #endif

    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;

    #if QT_VERSION < 0x040000
      application.setMainWidget(&viewer);
    #else
      viewer.setWindowTitle("constrainedCamera");
    #endif

      viewer.show();

      return application.exec();
    }

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Last modified on Thursday, December 19, 2013.