Most applications attempt to support WYSIWYG (what you see is what you get) output. This means that text drawn with a 10-point Helvetica bold font in the application window should have a similar appearance when it is printed. Obtaining true WYSIWYG output is virtually impossible and even undesirable in most cases. This is due, in part, to the differences in video and printer technologies; a pixel on a screen is generally larger than a dot on a common laser printer. Viewing distances are different as well; a computer user typically sits about two feet away from the screen, but a reader's eyes are usually one foot or less from the printed page.
To compensate for legibility differences between screens and the printed page, Windows and Windows NT support a unit called the logical inch that is always specified in pixels. For a video display, the logical inch is always greater than the physical inch to compensate for the longer viewing distance and the (generally) coarser resolution. For printers, the logical inch is always equal to the physical inch.
To obtain a WYSIWYG effect when drawing text, an application can use the CreateFont function to specify the typeface name and point size of an ideal (or logical) font and then call the SelectObject function to identify the display or printer DC. When the application calls SelectObject, the system selects a physical font that is the closest possible match to the specified logical font. When the system selects the display font, it chooses a physical font that is larger than the actual point size. From the user's perspective, however, it appears to be very close to the correct height. When the system selects the font for the printer, it chooses a physical font that is actually the requested point size. For more information about fonts and text output, see Fonts and Text.
To obtain a WYSIWYG effect when drawing bitmapped graphics, an application can retrieve the width and height, in logical inches, of the screen and the printed page. Using these values, the application can create horizontal and vertical scaling factors to maintain the proportion of bitmapped images when they are drawn on a printer. For an example that demonstrates this process, see WYSIWYG Display and Output. For more information about bitmaps and bitmap output, see Bitmaps.