clock.cpp

#include <QtWidgets>
#include "clock.h"

Clock::Clock(QWidget *parentWidgetPtr)
    :QWidget(parentWidgetPtr)
{
    setWindowTitle(tr("Clock"));
    resize(1000, 500);

    m_timer.setParent(this);
    connect(&m_timer, SIGNAL(timeout()), this, SLOT(update()));
    m_timer.start(100);
}

void Clock::paintEvent(QPaintEvent*)
{
    int side   = qMin(width(), height());
    QTime time = QTime::currentTime();

    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);
    painter.setRenderHint(QPainter::TextAntialiasing);
    painter.translate(width() / 2, height() / 2);
    painter.scale(side / 200.0, side / 200.0);

    for (int second = 0; second <= 60; ++second) {
        if ((second % 5 )  == 0) {
            painter.drawLine(QPoint(0, 81), QPoint(0, 98));
        } else {
            painter.drawLine(QPoint(0, 90), QPoint(0, 98));
        }

        painter.rotate(6);
    }

    double hours        = time.hour();
    double minutes      = time.minute();
    double seconds      = time.second();
    double milliseconds = time.msec();

    painter.setPen(Qt::black);
    painter.setBrush(Qt::gray);

    {
        static const QPoint hourHand[3] = {QPoint(8, 8), QPoint(-8, 8), QPoint(0, -60)};
        painter.save();

        double hour = hours + (minutes / 60.0) + (seconds / 3600.0) + (milliseconds / 3600000.0);
        painter.rotate(30.0 * hour);
        painter.drawConvexPolygon(hourHand, 3);
        painter.restore();
    }

    {
        static const QPoint minuteHand[3] = {QPoint(6, 8), QPoint(-6, 8), QPoint(0, -70)};
        painter.save();

        double minute = minutes + (seconds / 60.0) + (milliseconds / 60000.0);
        painter.rotate(6.0 * minute);
        painter.drawConvexPolygon(minuteHand, 3);
        painter.restore();
    }

    {
        static const QPoint secondHand[3] = {QPoint(4,8), QPoint(-4, 8), QPoint(0, -80)};
        painter.save();

        double second = seconds + (milliseconds / 1000);
        painter.rotate(6.0* second);
        painter.drawConvexPolygon(secondHand, 3);
        painter.restore();
    }
}