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 aliasing and so we can...