A.6 The class TScreen

With those preliminaries behind us we may advance more quickly towards our objectives. We have reached a point in Windows programming equivalent to that from which in DOS we began chapter 15, but from now on we can draw upon many of the details of that chapter. In particular, we want to derive from TWindow a class TScreen which will enable us to draw a function and map the screen with rather little extra work.

The construction of TScreen is summarized is Appendix H, which shows the header file screen.h. It begins with the usual header files, including those appropriate to OWL. It continues with a set of standard colour values of the form

   const COLORREF AColor = RGB (r, g, b);

where COLORREF is another name for a long unsigned integer, and RGB is a Windows function which constructs, subject to the capabilities of the output device, colours according to their red, green and blue components, each given as a byte.

There follow the _CLASSDEF macros for Point, Pixel, TScreen and TScreenApplication, the four classes in terms of which we translate chapter 15 into Windows terminology. For Point we choose

   class Point {   public:         double x, y;         Point()           ...