Time for action – drawing an oscillogram

Let's further extend our widget to become a simple oscillogram renderer. For that we have to make the widget remember a set of values and draw them as a series of lines.

Let's start by adding a QList<quint16> member variable that holds a list of unsigned 16-bit integer values. We will also add slots for adding values to the list and for clearing the list, as shown:

class Widget : public QWidget
{
  // ...
public slots:
  void addPoint(unsigned yVal) { m_points << qMax(0u, yVal); update(); }
  void clear() { m_points.clear(); update(); }
protected:
  // ...
  QList<quint16> m_points;
};

Note that each modification of the list invokes a method called update(). This schedules a paint event so that our widget can be redrawn with the new values.

Drawing code is also easy; we just iterate over the list and draw symmetric blue lines based on the values from the list. Since the lines are vertical, they don't suffer from...