OvenTimer from C++ GUI Programming with Qt4

// oventimer.h

#ifndef OVENTIMER_H
#define OVENTIMER_H

#include<QWidget>
#include<QDateTime>

class OvenTimer:public QWidget
{
  Q_OBJECT
 public:
  OvenTimer(QWidget *parent=0);
  void setDuration(int secs);
  int duration()const;
  void draw(QPainter *painter);
 signals:
  void timeout();
 protected:
  void paintEvent(QPaintEvent *event);
  void mousePressEvent(QMouseEvent *event);
 private:
  QDateTime finishTime;
  QTimer *updateTimer;
  QTimer *finishTimer;
};

#endif

#include<QtGui>
#include<math.h>
#include"oventimer.h"

const double DegreesPerMinute = 7.0;
const double DegreesPerSecond = DegreesPerMinute / 60;
const int MaxMinutes = 45;
const int MaxSeconds = MaxMinutes *60;
const int UpdateInterval = 1;

OvenTimer::OvenTimer(QWidget *parent)
  :QWidget(parent)
{
  finishTime = QDateTime::currentDateTime();
  updateTimer = new QTimer(this);
  connect(updateTimer,SIGNAL(timeout()),this,SLOT(update()));
  finishTimer = new QTimer(this);
  finishTimer->setSingleShot(true);
  connect(finishTimer,SIGNAL(timeout()),this,SLOT(timeout()));
  connect(finishTimer,SIGNAL(timeout()),updateTimer,SLOT(stop()));
}

void OvenTimer::setDuration(int secs)
{
  if(secs > MaxSeconds)
    secs = MaxSeconds;
  else if(secs <=0)
    secs = 0;
  finishTime = QDateTime::currentDateTime().addSecs(secs);
  if(secs > 0)
    {
     updateTimer->start(UpdateInterval * 1000);
     finishTimer->start(secs * 1000);
    }
  else
    {
     updateTimer->stop();
     finishTimer->stop();
    }
  update();
}

int OvenTimer::duration()const
{
  int secs = QDateTime::currentDateTime().secsTo(finishTime);
  if(secs < 0)
    secs = 0;
  return secs;
}

void OvenTimer::mousePressEvent(QMouseEvent *event)
{
  QPointF point = event->pos() - rect().center();
  double theta = atan2(-point.x(),-point.y())*180/3.14159265359;
  setDuration(duration()+int(theta/DegreesPerSecond));
  update();
}

void OvenTimer::paintEvent(QPaintEvent *event)
{
  QPainter painter(this);
  painter.setRenderHint(QPainter::Antialiasing ,true);
  int side = qMin(width(),height());
  painter.setViewport((width()-side)/2,(height()-side)/2,side,side);
  painter.setWindow(-50,-50,100,100);
  draw(&painter);
}

void OvenTimer::draw(QPainter *painter)
{
  static const int triangle[3][2] =
    {
     {-2,-49},{2,-49},{0,-47}
    };
  QPen thickPen(palette().foreground(),1.5);
  QPen thinPen(palette().foreground(),0.5);
  QColor niceBlue(150,150,200);
  painter->setPen(thinPen);
  painter->setBrush(palette().foreground());
  painter->drawPolygon(QPolygon(3,&triangle[0][0]));

  QConicalGradient coneGradient(0,0,-90.0);
  coneGradient.setColorAt(0.0,Qt::darkGray);
  coneGradient.setColorAt(0.2,niceBlue);
  coneGradient.setColorAt(0.5,Qt::white);
  coneGradient.setColorAt(1.0,Qt::darkGray);
  painter->setBrush(coneGradient);
  painter->drawEllipse(-46,-46,92,92);

  QRadialGradient haloGradient(0,0,20,0,0);
  haloGradient.setColorAt(0.0,Qt::lightGray);
  haloGradient.setColorAt(0.8,Qt::darkGray);
  haloGradient.setColorAt(0.9,Qt::white);
  haloGradient.setColorAt(1.0,Qt::black);
  painter->setPen(Qt::NoPen);
  painter->setBrush(haloGradient);
  painter->drawEllipse(-20,-20,40,40);

  QLinearGradient knobGradient(-7,-25,7,25);
  knobGradient.setColorAt(0.0,Qt::black);
  knobGradient.setColorAt(0.2,niceBlue);
  knobGradient.setColorAt(0.3,Qt::lightGray);
  knobGradient.setColorAt(0.8,Qt::white);
  knobGradient.setColorAt(1.0,Qt::black);
  painter->rotate(duration() * DegreesPerSecond);
  painter->setBrush(knobGradient);
  painter->setPen(thinPen);
  painter->drawRoundRect(-7,-25,14,50,150,50);
  for(int i=0;i<=MaxMinutes;++i)
    {
     if(i%5==0)
        {
         painter->setPen(thickPen);
         painter->drawLine(0,-41,0,-44);
         painter->drawText(-15,-41,30,25,
                            Qt::AlignHCenter|Qt::AlignTop,
                            QString::number(i));
        }
     else
        {
         painter->setPen(thinPen);
         painter->drawLine(0,-42,0,-44);
        }
     painter->rotate(-DegreesPerMinute);
    }
}