WidgetUpdate.hpp

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// Qt Graphical Objects & Multi-Thread

#ifndef QT_WIDGET_UPDATE
#define QT_WIDGET_UPDATE

#include <math.h>    // to get sqrt declaration
#include <iostream>  // to get std::cout declaration
#include <QWidget>
#include <QThread>

#ifdef BUGGY
class UpdateWidget;  // UpdateWidget declaration
#endif

class Updater : public QThread {
#ifndef BUGGY
  Q_OBJECT  // This macro is needed for the signal to get handled
#else
  UpdateWidget& widget;  
#endif

  bool still_running;  
    
  void run();
    
public:
#ifdef BUGGY
  Updater(UpdateWidget& parent) : widget(parent), 
#else
  Updater() : 
#endif
    still_running(false) { start(); }
    
  void stop() {
    still_running = false;  // ask to the run() method to stop
    wait();                 // when stopped, returns
  }

#ifndef BUGGY
Q_SIGNALS:
  void updatePosRequest(const int dist);
#endif
}; // end of class Updater


class UpdateWidget : public QWidget {
  Q_OBJECT  // This macro is needed to handle connect methods

  QPoint position;  
  QPoint aimed;     
  Updater updater;  
    
  QRect  region(const QPoint& pos, const bool big = false) const {
    static const int offset = 2 + (big ? 5 : 0); 
    return QRect(pos, pos).adjusted(-offset, -offset, offset, offset);
  }

  void modify(QPoint& variable, const QPoint& value) {
    // region modified in the drawing (union of two increased regions)
    const QRect  change  = region(variable, true)
      | region(value, true);
    // !!!Bug in Qt 4: remaining stains even whith increased regions!!!
    variable = value;    // update the variable
    /*    std::cout << "Update from thread "
      << QThread::currentThreadId() << std::endl; */
    update(change);      // update the drawing
    // !!!Feature: Qt crashes (SegV) at high frequency!!!
    // Everything seems fine with update() (but more expensive)...
  }
  
#ifdef BUGGY
public Q_SLOTS:
#else
private Q_SLOTS:
#endif
  void updatePosition(const int dist) {
    const QPointF new_pos = position, vector = new_pos - aimed;
    const qreal   x = vector.x(), y = vector.y(),
      distance = sqrt(x * x + y * y);
    if (distance > 1e-6) 
      modify( position, (new_pos - vector * dist /
             distance).toPoint() );
  }
  
public:
  UpdateWidget(QWidget* parent = 0)
    : QWidget(parent), 
#ifdef BUGGY
      updater(*this) 
#else
      updater() 
#endif
  { 
    setBackgroundRole(QPalette::Base);
#ifndef BUGGY
    connect( &updater, SIGNAL( updatePosRequest(const int) ),
         this, SLOT( updatePosition(const int) ) );
#endif 
  }

  ~UpdateWidget() { updater.stop(); }
  
  void init() {
    const QPoint center(width() / 2, height() / 2);
    modify(position, center);
    modify(aimed, center); /*
    std::cout << "Main thread " << QThread::currentThreadId()
    << std::endl; */
  }
  
protected:
  void paintEvent(QPaintEvent *event);
  
  void mouseMoveEvent(QMouseEvent *event);
  
}; // end of class UpdateWidget

#endif // QT_WIDGET_UPDATE