libQGLViewer multiSelect example

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# The multiSelect example

Customized `select()` function that enables the selection of several objects.

Object selection is preformed using the left mouse button. Press Shift to add objects to the selection, and Alt to remove objects from the selection.

Individual objects (click on them) as well as rectangular regions (click and drag mouse) can be selected. To do this, the selection region size is modified and the `endSelection()` function has been overloaded so that all the objects of the region are taken into account (the default implementation only selects the closest object).

The selected objects can then be manipulated by pressing the Control key. Other set operations (parameter edition, deletion...) can also easily be applied to the selected objects.

Since we use gluCylinder

## multiSelect.h

    #include "QGLViewer/qglviewer.h"
    #include "object.h"

    class Viewer : public QGLViewer {
    public:
      Viewer();

    protected:
      virtual void draw();
      virtual void init();
      virtual QString helpString() const;

      // Selection functions
      virtual void drawWithNames();
      virtual void endSelection(const QPoint &);

      // Mouse events functions
      virtual void mousePressEvent(QMouseEvent *e);
      virtual void mouseMoveEvent(QMouseEvent *e);
      virtual void mouseReleaseEvent(QMouseEvent *e);

    private:
      void startManipulation();
      void drawSelectionRectangle() const;
      void addIdToSelection(int id);
      void removeIdFromSelection(int id);

      // Current rectangular selection
      QRect rectangle_;

      // Different selection modes
      enum SelectionMode { NONE, ADD, REMOVE };
      SelectionMode selectionMode_;

      QList<Object *> objects_;
      QList<int> selection_;
    };

## multiSelect.cpp

    #include "multiSelect.h"
    #include "manipulatedFrameSetConstraint.h"

    #include <QGLViewer/manipulatedFrame.h>

    #include <QMouseEvent>

    using namespace qglviewer;

    Viewer::Viewer() {
      selectionMode_ = NONE;

      // Fill the scene with objects positionned on a regular grid.
      // Consider increasing selectBufferSize() if you use more objects.
      const int nb = 10;
      for (int i = -nb; i <= nb; ++i)
        for (int j = -nb; j <= nb; ++j) {
          Object *o = new Object();
          o->frame.setPosition(Vec(i / float(nb), j / float(nb), 0.0));
          objects_.append(o);
        }
    }

    void Viewer::init() {
      // A ManipulatedFrameSetConstraint will apply displacements to the selection
      setManipulatedFrame(new ManipulatedFrame());
      manipulatedFrame()->setConstraint(new ManipulatedFrameSetConstraint());

      // Used to display semi-transparent relection rectangle
      glBlendFunc(GL_ONE, GL_ONE);

      restoreStateFromFile();
      help();
    }

    QString Viewer::helpString() const {
      QString text("<h2>m u l t i S e l e c t </h2>");
      text += "This example illustrates an application of the "
              "<code>select()</code> function that ";
      text += "enables the selection of several objects.<br><br>";
      text += "Object selection is preformed using the left mouse button. Press "
              "<b>Shift</b> to add objects ";
      text += "to the selection, and <b>Alt</b> to remove objects from the "
              "selection.<br><br>";
      text += "Individual objects (click on them) as well as rectangular regions "
              "(click and drag mouse) can be selected. ";
      text += "To do this, the selection region size is modified and the "
              "<code>endSelection()</code> function ";
      text += "has been overloaded so that <i>all</i> the objects of the region "
              "are taken into account ";
      text +=
          "(the default implementation only selects the closest object).<br><br>";
      text += "The selected objects can then be manipulated by pressing the "
              "<b>Control</b> key. ";
      text += "Other set operations (parameter edition, deletion...) can also "
              "easily be applied to the selected objects.";
      return text;
    }

    //  D r a w i n g   f u n c t i o n

    void Viewer::draw() {
      // Draws selected objects only.
      glColor3f(0.9f, 0.3f, 0.3f);
      for (QList<int>::const_iterator it = selection_.begin(),
                                      end = selection_.end();
           it != end; ++it)
        objects_.at(*it)->draw();

      // Draws all the objects. Selected ones are not repainted because of GL depth
      // test.
      glColor3f(0.8f, 0.8f, 0.8f);
      for (int i = 0; i < int(objects_.size()); i++)
        objects_.at(i)->draw();

      // Draws manipulatedFrame (the set's rotation center)
      if (manipulatedFrame()->isManipulated()) {
        glPushMatrix();
        glMultMatrixd(manipulatedFrame()->matrix());
        drawAxis(0.5);
        glPopMatrix();
      }

      // Draws rectangular selection area. Could be done in postDraw() instead.
      if (selectionMode_ != NONE)
        drawSelectionRectangle();
    }

    //   C u s t o m i z e d   m o u s e   e v e n t s

    void Viewer::mousePressEvent(QMouseEvent *e) {
      // Start selection. Mode is ADD with Shift key and TOGGLE with Alt key.
      rectangle_ = QRect(e->pos(), e->pos());

      if ((e->button() == Qt::LeftButton) && (e->modifiers() == Qt::ShiftModifier))
        selectionMode_ = ADD;
      else if ((e->button() == Qt::LeftButton) &&
               (e->modifiers() == Qt::AltModifier))
        selectionMode_ = REMOVE;
      else {
        if (e->modifiers() == Qt::ControlModifier)
          startManipulation();
        QGLViewer::mousePressEvent(e);
      }
    }

    void Viewer::mouseMoveEvent(QMouseEvent *e) {
      if (selectionMode_ != NONE) {
        // Updates rectangle_ coordinates and redraws rectangle
        rectangle_.setBottomRight(e->pos());
        update();
      } else
        QGLViewer::mouseMoveEvent(e);
    }

    void Viewer::mouseReleaseEvent(QMouseEvent *e) {
      if (selectionMode_ != NONE) {
        // Actual selection on the rectangular area.
        // Possibly swap left/right and top/bottom to make rectangle_ valid.
        rectangle_ = rectangle_.normalized();
        // Define selection window dimensions
        setSelectRegionWidth(rectangle_.width());
        setSelectRegionHeight(rectangle_.height());
        // Compute rectangle center and perform selection
        select(rectangle_.center());
        // Update display to show new selected objects
        update();
      } else
        QGLViewer::mouseReleaseEvent(e);
    }

    //   C u s t o m i z e d   s e l e c t i o n   p r o c e s s

    void Viewer::drawWithNames() {
      for (int i = 0; i < int(objects_.size()); i++) {
        glPushName(i);
        objects_.at(i)->draw();
        glPopName();
      }
    }

    void Viewer::endSelection(const QPoint &) {
      // Flush GL buffers
      glFlush();

      // Get the number of objects that were seen through the pick matrix frustum.
      // Reset GL_RENDER mode.
      GLint nbHits = glRenderMode(GL_RENDER);

      if (nbHits > 0) {
        // Interpret results : each object created 4 values in the selectBuffer().
        // (selectBuffer())[4*i+3] is the id pushed on the stack.
        for (int i = 0; i < nbHits; ++i)
          switch (selectionMode_) {
          case ADD:
            addIdToSelection((selectBuffer())[4 * i + 3]);
            break;
          case REMOVE:
            removeIdFromSelection((selectBuffer())[4 * i + 3]);
            break;
          default:
            break;
          }
      }
      selectionMode_ = NONE;
    }

    void Viewer::startManipulation() {
      Vec averagePosition;
      ManipulatedFrameSetConstraint *mfsc =
          (ManipulatedFrameSetConstraint *)(manipulatedFrame()->constraint());
      mfsc->clearSet();

      for (QList<int>::const_iterator it = selection_.begin(),
                                      end = selection_.end();
           it != end; ++it) {
        mfsc->addObjectToSet(objects_[*it]);
        averagePosition += objects_[*it]->frame.position();
      }

      if (selection_.size() > 0)
        manipulatedFrame()->setPosition(averagePosition / selection_.size());
    }

    //   S e l e c t i o n   t o o l s

    void Viewer::addIdToSelection(int id) {
      if (!selection_.contains(id))
        selection_.push_back(id);
    }

    void Viewer::removeIdFromSelection(int id) { selection_.removeAll(id); }

    void Viewer::drawSelectionRectangle() const {
      startScreenCoordinatesSystem();
      glDisable(GL_LIGHTING);
      glEnable(GL_BLEND);

      glColor4f(0.0, 0.0, 0.3f, 0.3f);
      glBegin(GL_QUADS);
      glVertex2i(rectangle_.left(), rectangle_.top());
      glVertex2i(rectangle_.right(), rectangle_.top());
      glVertex2i(rectangle_.right(), rectangle_.bottom());
      glVertex2i(rectangle_.left(), rectangle_.bottom());
      glEnd();

      glLineWidth(2.0);
      glColor4f(0.4f, 0.4f, 0.5f, 0.5f);
      glBegin(GL_LINE_LOOP);
      glVertex2i(rectangle_.left(), rectangle_.top());
      glVertex2i(rectangle_.right(), rectangle_.top());
      glVertex2i(rectangle_.right(), rectangle_.bottom());
      glVertex2i(rectangle_.left(), rectangle_.bottom());
      glEnd();

      glDisable(GL_BLEND);
      glEnable(GL_LIGHTING);
      stopScreenCoordinatesSystem();
    }

## manipulatedFrameSetConstraint.h

    #include "QGLViewer/constraint.h"
    #include "object.h"

    class ManipulatedFrameSetConstraint : public qglviewer::Constraint {
    public:
      void clearSet();
      void addObjectToSet(Object *o);

      virtual void constrainTranslation(qglviewer::Vec &translation,
                                        qglviewer::Frame *const frame);
      virtual void constrainRotation(qglviewer::Quaternion &rotation,
                                     qglviewer::Frame *const frame);

    private:
      QList<Object *> objects_;
    };

## object.h

    #ifndef OBJECT_H_
    #define OBJECT_H_

    #include "QGLViewer/frame.h"

    class Object {
    public:
      void draw() const;
      qglviewer::Frame frame;
    };

    #endif // OBJECT_H_

## main.cpp

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

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

      Viewer viewer;

      viewer.setWindowTitle("multiSelect");

      viewer.show();

      return application.exec();
    }

## manipulatedFrameSetConstraint.cpp

    #include "manipulatedFrameSetConstraint.h"
    #include "QGLViewer/frame.h"

    using namespace qglviewer;

    void ManipulatedFrameSetConstraint::clearSet() { objects_.clear(); }

    void ManipulatedFrameSetConstraint::addObjectToSet(Object *o) {
      objects_.append(o);
    }

    void ManipulatedFrameSetConstraint::constrainTranslation(
        qglviewer::Vec &translation, Frame *const) {
      for (QList<Object *>::iterator it = objects_.begin(), end = objects_.end();
           it != end; ++it)
        (*it)->frame.translate(translation);
    }

    void ManipulatedFrameSetConstraint::constrainRotation(
        qglviewer::Quaternion &rotation, Frame *const frame) {
      // A little bit of math. Easy to understand, hard to guess (tm).
      // rotation is expressed in the frame local coordinates system. Convert it
      // back to world coordinates.
      const Vec worldAxis = frame->inverseTransformOf(rotation.axis());
      const Vec pos = frame->position();
      const float angle = rotation.angle();

      for (QList<Object *>::iterator it = objects_.begin(), end = objects_.end();
           it != end; ++it) {
        // Rotation has to be expressed in the object local coordinates system.
        Quaternion qObject((*it)->frame.transformOf(worldAxis), angle);
        (*it)->frame.rotate(qObject);

        // Comment these lines only rotate the objects
        Quaternion qWorld(worldAxis, angle);
        // Rotation around frame world position (pos)
        (*it)->frame.setPosition(pos +
                                 qWorld.rotate((*it)->frame.position() - pos));
      }
    }

## object.cpp

    #include "object.h"

    using namespace qglviewer;

    void Object::draw() const {
      static GLUquadric *quad = gluNewQuadric();

      glPushMatrix();
      glMultMatrixd(frame.matrix());
      gluSphere(quad, 0.03, 10, 6);
      gluCylinder(quad, 0.03, 0.0, 0.09, 10, 1);
      glPopMatrix();
    }

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