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Graphics Device Interface (GDI)

Started by sukishan, Jul 12, 2009, 06:38 PM

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Graphics Device Interface (GDI)

The graphics device interface (GDI) provides functions and related structures that an application can use to generate graphical output for displays, printers, and other devices. Using GDI functions, you can draw lines, curves, closed figures, paths, text, and bitmap images. The color and style of the items you draw depends on the drawing objects — that is, pens, brushes, and fonts — that you create. You can use pens to draw lines and curves, brushes to fill the interiors of closed figures, and fonts to write text.

Applications direct output to a specified device by creating a device context (DC) for the device. The device context is a GDI-managed structure containing information about the device, such as its operating modes and current selections. An application creates a DC by using device context functions. GDI returns a device context handle, which is used in subsequent calls to identify the device. For example, using the handle, an application can retrieve information about the capabilities of the device, such as its technology type (display, printer, or other device) and the dimensions and resolution of the display surface.

Applications can direct output to a physical device, such as a display or printer, or to a "logical" device, such as a memory device or metafile. Logical devices give applications the means to store output in a form that is easy to send subsequently to a physical device. After an application records output in a metafile, it can play that metafile any number of times, sending the output to any number of physical devices.

Applications use attribute functions to set the operating modes and current selections for the device. The operating modes include the text and background colors, the mixing mode (also called the binary raster operation) that specifies how colors in a pen or brush combine with colors already on the display surface, and the mapping mode that specifies how GDI maps the coordinates used by the application to the coordinate system of the device.
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