libQGLViewer mouseGrabber example

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# The mouseGrabber example

`MouseGrabber`s enable complex mouse interaction.

A `MouseGrabber` is an abstract class which defines objects that are sensitive to the mouse. When activated, they grab the mouse events. Possible applications are interactive 2D or 3D GUI, object auto-selection, auto drop-down menu and much more.

`ManipulatedFrame` are indeed `MouseGrabbers` as is illustrated here. Simply hover on a spiral to automatically "select" it. Mouse events will then be grabbed by the associated `ManipulatedFrame`, which can be moved without any key press or GUI interaction. Useful to easily manipulate scene objects. Note that by default, a `ManipulatedFrame` grabs the mouse when the cursor is close enough to its `position()`. You may want to overload the `checkIfGrabsMouse()` function to define a more complex grabbing test.

That's what is done in the `CameraPathPlayer` class, which is associated to a Camera keyFrame paths or position. It is displayed as a text on the left hand side of the window (when its associated path is defined). It reacts to mouse hovering and clicking the text will play (resp. restore) the Camera path (resp. position).

## mouseGrabber.h

    #include <QGLViewer/manipulatedFrame.h>
    #include <QGLViewer/mouseGrabber.h>
    #include <QGLViewer/qglviewer.h>

    class CameraPathPlayer : public qglviewer::MouseGrabber {
    public:
      CameraPathPlayer(int nb) : pathNb(nb) {}
      void checkIfGrabsMouse(int x, int y, const qglviewer::Camera *const camera);
      int yPos() { return 25 * pathNb; }

    protected:
      void mousePressEvent(QMouseEvent *const, qglviewer::Camera *const camera) {
        camera->playPath(pathNb);
      }

    private:
      int pathNb;
    };

    class Spiral {
    public:
      void draw() const;
      void setPosition(const qglviewer::Vec &pos) { mf_.setPosition(pos); };

    private:
      qglviewer::ManipulatedFrame mf_;
    };

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

      void displayPlayers();
      void updatePlayers();

    private:
      CameraPathPlayer **player_;
      int nbPlayers_;
      QList<Spiral> spiral_;
    };

## mouseGrabber.cpp

    #include "mouseGrabber.h"

    #include <QGLViewer/manipulatedFrame.h>

    using namespace qglviewer;
    using namespace std;

    void CameraPathPlayer::checkIfGrabsMouse(int x, int y, const Camera *const) {
      // Rectangular activation array - May have to be tune depending on your
      // default font size
      setGrabsMouse((x < 80) && (y < yPos()) && ((yPos() - y) < 16));
    }

    void Viewer::displayPlayers() {
      for (int i = 0; i < nbPlayers_; ++i) {
        CameraPathPlayer *cpp = player_[i];
        if (cpp) {
          QString s;
          if (cpp->grabsMouse()) {
            glColor3f(1, 1, 1);
            if (camera()->keyFrameInterpolator(i)->numberOfKeyFrames() > 1)
              s = "Play path F" + QString::number(i);
            else
              s = "Restore pos F" + QString::number(i);
          } else {
            glColor3f(0.6f, 0.6f, 0.6f);
            if (camera()->keyFrameInterpolator(i)->numberOfKeyFrames() > 1)
              s = "Path F" + QString::number(i);
            else
              s = "Pos F" + QString::number(i);
          }
          drawText(10, cpp->yPos() - 3, s);
        }
      }
    }

    void Viewer::updatePlayers() {
      for (int i = 0; i < nbPlayers_; ++i) {
        // Check if CameraPathPlayer is still valid
        if ((player_[i]) && (!camera()->keyFrameInterpolator(i))) {
          delete player_[i];
          player_[i] = NULL;
        }
        // Or add it if needed
        if ((camera()->keyFrameInterpolator(i)) && (!player_[i]))
          player_[i] = new CameraPathPlayer(i);
      }
    }

    void Viewer::init() {
      // Absolutely needed for MouseGrabber
      setMouseTracking(true);

      // In order to make the manipulatedFrame displacements clearer
      setAxisIsDrawn();

      // Initialize the CameraPathPlayer MouseGrabber array
      nbPlayers_ = 12;
      player_ = new CameraPathPlayer *[nbPlayers_];
      for (int i = 0; i < nbPlayers_; ++i)
        player_[i] = NULL;

      // Create a scene with several spirals.
      const int nbSpirals = 7;
      for (int i = -nbSpirals / 2; i <= nbSpirals / 2; ++i) {
        Spiral s;
        s.setPosition(Vec(1.8f * i / nbSpirals, 0.0, 0.0));
        spiral_.push_back(s);
      }

      restoreStateFromFile();

      help();
    }

    void Viewer::draw() {
      for (QList<Spiral>::const_iterator it = spiral_.begin(), end = spiral_.end();
           it != end; ++it)
        (*it).draw();

      updatePlayers();
      glDisable(GL_LIGHTING);
      displayPlayers();
      glEnable(GL_LIGHTING);
    }

    QString Viewer::helpString() const {
      QString text("<h2>M o u s e G r a b b e r </h2>");
      text += "This example illustrates the use of <i>MouseGrabber</i>, which is "
              "an abstract ";
      text += "class for objects that react (usually when the mouse hovers over "
              "them).<br><br>";
      text += "Define new camera paths (or positions) using "
              "<b>Alt</b>+[<b>F1</b>-<b>F12</b>]. ";
      text += "New <i>MouseGrabbers</i> are then created and displayed in the "
              "upper left corner. ";
      text += "Note how they react when the mouse hovers, and click them to play "
              "the associated path.<br><br>";
      text += "<i>ManipulatedFrame</i>, such as the ones which define the spirals' "
              "positions, are ";
      text += "also <i>MouseGrabbers</i>. When the mouse is close to the spiral "
              "center, the <i>ManipulatedFrame</i> ";
      text += "will grab to mouse click (as if the <b>Control</b> key was "
              "pressed). This is very convenient ";
      text += "to intuitively move scene objects (such as lights) without any key "
              "or GUI interaction.<br><br>";
      text += "Note that <code>setMouseTracking()</code> must be enabled to use "
              "<i>MouseGrabbers</i>.";
      return text;
    }

    void Spiral::draw() const {
      glPushMatrix();
      glMultMatrixd(mf_.matrix());

      // Draw a spiral
      const float nbSteps = 100.0;
      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 = 0.2 - 0.15 * ratio;
        float r2 = 0.16 - 0.15 * ratio;
        float alt = 0.2f * (ratio - 0.5);
        const float nor = .5;
        const float up = sqrt(1.0 - nor * nor);

        if (mf_.grabsMouse())
          glColor3f(1 - ratio, 0.8f, ratio / 2.0);
        else
          glColor3f(1 - ratio, 0.2f, ratio);

        glNormal3f(nor * c, up, nor * s);
        glVertex3f(r1 * c, alt, r1 * s);
        glVertex3f(r2 * c, alt + 0.01, r2 * s);
      }
      glEnd();

      glPopMatrix();
    }

## main.cpp

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

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

      Viewer viewer;

      viewer.setWindowTitle("mouseGrabber");

      viewer.show();

      return application.exec();
    }

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