A group of five of us decided to implement a board game called Scotland Yard, where detectives try to track down a spy as he travels by bus, cab, and tube throughout the city of London. Some screen shots appear to the left. As you can see, they are full of check boxes, buttons, and dialogs.
What is most remarkable about this project is that we implemented it all on top of the very simple Borland Graphics Library for DOS+VGA. It supports drawing lines, circles, and the primitive text fonts you see. Beyond that, we rolled our own GUI toolkit!
For kicks, I ran all the source code through Doxygen (fantastic tool!), so you can browse it online. Here are pointers to some of the most interesting aspects:
- Most GUI programming today is event-based. We defined our own Messages for keyboard events,
mouse activity, button presses, etc.
- A Display is a Viewport which can contain Screen Objects such as Windows and Buttons.
- When the user clicks the mouse on the screen, the root display
receives the event, and dispatches it to each of its
children (all screen objects), in
turn, until one acknowledges the event. Generally, a screen
object determine whether they should handle the event based on its
coordinates. Here is the dispatch routine for
buttons.
- We used multiple inheritance to model the players, since there are
two kinds of players: spy and detectives, each of which can be
controlled either by human or computer. (Better OO design patterns
weren’t well publicized at the time!)
- We defined an enum bool
because the boolean type was not standard in C++ in those days!
Probably several other modifications are necessary to compile our code
with modern C++ tools.