Display Drivers and Background Drawing to Memory Bitmaps

• Microsoft Windows Device Driver Kit (DDK) for Windows versions 3.0, 3.1, and 3.11

In the Microsoft Windows graphical environment, a display driver must support all of its declared capabilities at all times, regardless of the current video mode of the adapter. For example, when Windows is running in enhanced mode, a display driver can be called to perform graphics operations on a memory bitmap while a full-screen MS-DOS (non-Windows) application is running in the foreground. This may occur if an application developed for Windows is printing in the background, and the graphics device interface (GDI) calls the display driver to perform some imaging for the current page.

If the display driver relies on adapter hardware for certain graphics operations, but cannot access this hardware due to the current video mode of the adapter, then the driver must include "host side" drawing to handle this case.

The 8514/A display driver provides an example of hardware operations emulated in host code when drawing to main memory bitmaps. This source code is available in the Windows Device Development Kit (DDK) versions 3.0 and 3.1.