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Introduction to Writing Windows CE Display Drivers(3)
In Windows, bitmaps are used to represent graphical images. A bitmap typically contains the pixel data for the image, the dimensions and color depth of the image, and possibly the palette for the image, among other things. Information in a Windows bitmap is not directly available, but is abstracted and only accessible through calls to Win32 APIs. A Windows CE display driver typically sees bitmaps in a format called a surface. These surfaces contain the information of the bitmap, but in a format that is directly accessible by the display driver.
If you require additional background information before getting started on display driver development, there are plenty of good video and graphics books available to cover the basics of these topics in more detail.
Display Driver OverviewThe Graphics Device Interface, or GDI, is the system component that loads and calls the display driver. It is also where bit block transfers, or blits, and drawing related Win32 APIs are handled. In Windows CE, GDI is contained in the Graphic, Windowing, and Event Subsystem, or GWES. An interesting thing to note is that in Windows CE, GWES is an optional component, making the display driver optional as well. It is therefore possible to make Windows CE devices that are "headless", that is, with no graphic display interface. This is useful to be aware of when writing other device drivers since you may not be able to depend on having access to graphical objects, such as dialog boxes, to communicate with the user.
The display driver is a native driver in Windows CE. This means that it has a custom interface that provides a standard set of functionality for display devices. As a matter of fact, this display device driver interface, or DDI, is a subset of the Windows NT DDI. One of the major differences is that all Windows CE display drivers have the same level of functionality, so there is no "punting" of complex operations back to GDI. A windows CE display driver has only one function that it is required to export, DrvEnableDriver(). This function is called by GDI when the driver is loaded and is responsible for returning pointers to the other DDI functions.
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