In Windows, there are device (physical) and logical coordinates. There are several logical coordinate mapping systems in Windows. The simplest one is the text system; it simply maps one physical unit to the size of a pixel, which means that graphical figures will have different size monitors with different sizes or resolutions. This system is used in the Ring and Tetris applications.

The metric system maps one physical unit to a tenth of a millimeter (low metric) or a hundredth of a millimeter (high metric). The Draw, Calc, and Word applications of this book use the high metric system. There is also the British system that maps one physical unit to a hundredth of an inch (low English) or a thousandth of an inch (high English). The British system is not used in this book.

The position of a mouse click is always given in device units. When a part of the client area is invalidated (marked for repainting), the coordinates are also given in device units, and when we create...