ID Number: Q77402
3.00
WINDOWS
Summary:
In general, a Windows application cannot call the Windows display
driver directly to perform graphics primitives. This article details
the reasons this restriction is in place.
More Information:
The Windows display driver communicates with the Graphics Device
Interface (GDI) to perform primitive graphics operations. The
parameters of the entry points (or exported functions) in the display
driver are set up according to the standard interface between GDI and
the display driver. The parameters passed by GDI to the display driver
are only meaningful to GDI and to the display driver. A Windows
application has no way to obtain these parameters. For example, the
parameter most-commonly passed by GDI to the display driver is a
pointer to a structure called PDEVICE. Memory for this structure is
allocated by GDI, and its contents are specified by the display driver
during the driver's initialization. The pointer to the PDEVICE
structure is private to GDI; furthermore, the structure of PDEVICE
varies among display drivers.
To give another example, when a primitive is to be done to a memory
bitmap, instead of passing a pointer to PDEVICE, GDI passes to the
display driver a pointer to a structure; the structure is usually
referred to as a physical bitmap. Note that this physical bitmap
structure is also called "BITMAP"; do not confuse it with the BITMAP
structure defined in the Windows Software Development Kit. Again, this
physical bitmap structure is not designed to be used by a Windows
application. Although the information described in this structure is
somewhat related to the bitmap that the application uses, the pointer
to the physical bitmap structure is private to GDI and cannot be
obtained by the application.