In this exercise, we did two things. First, we provided a number of methods for calculating the geometry of important parts of the chess board and the size of the widget. Second, we defined three virtual methods for rendering visual primitives of a chess board. By making the methods virtual, we provided an infrastructure to let the look be customized by subclassing and overriding base implementations. Furthermore, by reading color from QPalette, we allowed customizing the colors of the primitives even without subclassing.
The last line of the main window constructor tells the layout of the window to force a fixed size of the window equal to what the size hint of the widget inside it reports.
