Coordinate transformation

In this example, we will learn how to use coordinate transformation and a timer to create a real-time clock display.

How to do it…

To create our first graphical clock display, let’s follow these steps:

1. First, create a new Qt Widgets Application project. Then, open up mainwindow.ui and remove the menuBar, mainToolBar, and statusBar as we did before.
2. After that, open up the mainwindow.h file and include the following headers:

   #include <QTime>
   #include <QTimer>
   #include <QPainter>

3. Then, declare the paintEvent() function, like so:

   public:
       explicit MainWindow(QWidget *parent = 0);
       ~MainWindow();
       virtual void paintEvent(QPaintEvent *event);

4. In the mainwindow.cpp file, create three arrays to store the shapes of the hour hand, minute hand, and second hand, where each of the arrays contains three sets of coordinates:

   void MainWindow::paintEvent...