Graphic output devices Foundation
In order to make the graphic output in a presentation space of a GUI application visible, the presentation space must be linked to a device context. A device context contains all device dependent information required for output of a drawing on an output device. In most cases the display of graphics occurs in a window on the screen. A window represents a device context. The GRA engine and its functions do not need to consider either a presentation space or a device context as long as the output occurs on the screen in an XbpCrt window. But the output of a graphic can also occur to a file or printer. In this case, a corresponding device context must be associated with a presentation space. Output to a printer is extremely device dependent. It requires the correct installation of a printer driver in the workplace shell. A printer is used for output in Xbase++ by an object of the XbpPrinter() class. XbpPrinter objects prepare a device context for graphic output to a printer. If the output is to be sent to a file, a decision must be made whether the file will contain a metafile or a raster image (bitmap). Both types of files contain graphic data and there are object classes to manage the file formats for both file formats. These classes are: XbpMetafile() and XbpBitmap(), respectively.
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