2.4 Programming Considerations

The major programming considerations are as follows:

• Keyboards are the greatest variable between different manufacturer’s workstations. If you want your program to be portable, you should be particularly conservative here.
• Many display systems have limited amounts of off-screen memory. If you can, you should minimize use of pixmaps and backing store.
• The user should have control of his screen real-estate. Therefore, you should write your applications to react to window management, rather than presume control of the entire screen. What you do inside of your top level window, however, is up to your application.
• Coordinates and sizes in X are actually 16-bit quantities. They usually are declared as an int16 (see int16) in the functions. Values larger than 16 bits can be truncated silently. Sizes (width and height) are unsigned quantities.
• The types color (see color), colormap (see colormap), cursor (see cursor), display (see display), font (see font), gcontext (see gcontext), pixmap (see pixmap), screen (see screen), and window (see window) are defined solely by a functional interface. Even though they are treated like structures in this document, it is not specified whether they are implemented as structures or classes. Although some interfaces are described as functions, they are not required to be defined using defun. (It is a requirement that they be functions as opposed to macros or special forms.)