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# The constrainedFrame example

Constraints can limit the translation and/or rotation of a (Manipulated)Frame.

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, Camera or Local) which defines the constraint directions.

Press the Control key while moving the mouse to move the camera.

## constrainedFrame.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;

      qglviewer::ManipulatedFrame* frame;

      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[3];
      unsigned short activeConstraint;
    };

## constrainedFrame.cpp

    #include "constrainedFrame.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::AXIS  : return AxisPlaneConstraint::FORBIDDEN;  break;
        case AxisPlaneConstraint::PLANE :
        case AxisPlaneConstraint::FORBIDDEN : return AxisPlaneConstraint::FREE; break;
        default : return AxisPlaneConstraint::FREE;
        }
    }

    void Viewer::changeConstraint()
    {
      unsigned short previous = activeConstraint;
      activeConstraint = (activeConstraint+1)%3;

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

      frame->setConstraint(constraints[activeConstraint]);
    }

    void Viewer::init()
    {
      constraints[0] = new LocalConstraint();
      constraints[1] = new WorldConstraint();
      constraints[2] = new CameraConstraint(camera());

      transDir = 0; // X direction
      rotDir   = 0; // X direction
      activeConstraint = 0;

      frame = new ManipulatedFrame();
      setManipulatedFrame(frame);
      frame->setConstraint(constraints[activeConstraint]);

    #if QT_VERSION < 0x040000
      // Preserve CAMERA bindings, see setHandlerKeyboardModifiers documentation.
      setHandlerKeyboardModifiers(QGLViewer::CAMERA, Qt::AltButton);
      // The frames can be move without any key pressed
      setHandlerKeyboardModifiers(QGLViewer::FRAME, Qt::NoButton);
      // The camera can always be moved with the Control key.
      setHandlerKeyboardModifiers(QGLViewer::CAMERA, Qt::ControlButton);

      setMouseBinding(Qt::ShiftButton | Qt::LeftButton,  QGLViewer::FRAME, QGLViewer::ROTATE,    false);
      setMouseBinding(Qt::ShiftButton | Qt::RightButton, QGLViewer::FRAME, QGLViewer::TRANSLATE, false);
      setMouseBinding(Qt::ShiftButton | Qt::MidButton,   QGLViewer::FRAME, QGLViewer::ZOOM,      false);
      setWheelBinding(Qt::ShiftButton,                   QGLViewer::FRAME, QGLViewer::ZOOM,      false);
    #else
      setHandlerKeyboardModifiers(QGLViewer::CAMERA, Qt::AltModifier);
      setHandlerKeyboardModifiers(QGLViewer::FRAME, Qt::NoModifier);
      setHandlerKeyboardModifiers(QGLViewer::CAMERA, Qt::ControlModifier);

      setMouseBinding(Qt::ShiftModifier | Qt::LeftButton,  QGLViewer::FRAME, QGLViewer::ROTATE,    false);
      setMouseBinding(Qt::ShiftModifier | Qt::RightButton, QGLViewer::FRAME, QGLViewer::TRANSLATE, false);
      setMouseBinding(Qt::ShiftModifier | Qt::MidButton,   QGLViewer::FRAME, QGLViewer::ZOOM,      false);
      setWheelBinding(Qt::ShiftModifier,                   QGLViewer::FRAME, QGLViewer::ZOOM,      false);
    #endif

      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");

      restoreStateFromFile();
      help();
    }

    void Viewer::draw()
    {
      glMultMatrixd(frame->matrix());
      drawAxis(0.4f);
      const float scale = 0.3f;
      glScalef(scale, scale, scale);

      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*scale, up*scale, nor*s*scale);
          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 LOCAL (SPACE)"); break;
        case 1 : drawText(20,20, "Constraint direction defined w/r to WORLD (SPACE)"); break;
        case 2 : 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 F r a m e</h2>");
      text += "A manipulated frame can be constrained in its displacement.<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 frame with the mouse.<br><br>";
      text += "The constraints can be defined with respect to various coordinates";
      text += "systems : press <b>Space</b> to switch.<br><br>";
      text += "Press the <b>Control</b> key while moving the mouse to move the camera.<br>";
      text += "Press the <b>Shift</b> key to temporally disable the constraint.<br><br>";
      text += "You can easily define your own constraints to create a specific frame behavior.";
      return text;
    }

## main.cpp

    #include "constrainedFrame.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("constrainedFrame");
    #endif

      viewer.show();

      return application.exec();
    }

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Last modified on Sunday, February 28, 2010.