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The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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GDI enables operation of the printer driver by calling the driver's Enable
function and directing the driver to initialize a physical device for
subsequent graphics output. A physical device is a PDEVICE structure that
represents a printer and its current operating state. A printer driver uses
the physical-device information to determine how to carry out specific
tasks, such as which device-dependent graphics commands to use, and which
output port to send the commands. The printer driver initializes the
physical device by copying information to the PDEVICE structure.
 
GDI calls the Enable function whenever an application calls the CreateDC
function (GDI.53) to create a device context (DC) for the printer. GDI calls
the function twice: once to retrieve a copy of the driver's GDIINFO
structure, and a second time to initialize the PDEVICE structure. After the
first call, GDI uses the dpDEVICEsize member in the GDIINFO structure to
determine the size of the driver's PDEVICE structure. GDI then allocates
memory for the structure and calls Enable for the second time, passing a
pointer to the structure. With this call, the driver initializes the
structure.
 
To initialize the PDEVICE structure, the driver typically examines the names
of the printer model and output device or file passed to Enable by GDI. It
may also examine any printer environment passed to Enable. The driver then
fills the PDEVICE structure with all the information that the output
functions need to generate appropriate graphics commands for the given
printer model and to send the commands to the given device or file.
 
Although only the printer driver initializes and uses the PDEVICE structure,
GDI allocates memory for the structure, determines when to pass it to the
driver's output functions, and deletes the structure when it is no longer
needed. Except for the first 16 bits of the PDEVICE structure, the content
and format of the structure depends entirely on the printer driver. The
first 16 bits, on the other hand, must be set to a nonzero value. GDI
reserves zero to indicate a BITMAP structure. GDI creates and uses a BITMAP
structure in place of a PDEVICE structure when an application creates a
memory-device context.
 
A printer driver can allocate additional structures and store their
addresses in the PDEVICE structure. Because GDI may direct a printer driver
to create a large number of physical devices, the printer driver should not
allocate additional structures in the limited space of the driver's
automatic data segment, especially if the driver allows multiple device
contexts.
 
GDI disables the physical device and possibly frees the printer driver
whenever an application calls the DeleteDC function (GDI.68). GDI disables
the physical device by calling the driver's Disable function. It expects the
driver to complete any outstanding printing job and free any resources
associated with the physical device. After the driver returns from the
Disable function, GDI frees the memory it allocated for the PDEVICE
structure. If there are no other device contexts for this printer driver,
Windows frees the driver, removing any driver code and data from memory.
 
 
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