User Objects

GDI maintains important internal data structures, but gives the driver access to the public fields of these structures by passing them down as user objects. User objects are intermediate data structures that provide an interface between GDI data structures and the drivers that need access to the information within these structures. The driver can pass the pointer to a user object back to GDI to query for information or to ask for various services. User objects with public fields provide the following advantages:

They eliminate problems associated with direct access to internal GDI data structures.
They provide a place to hold GDI data for the driver. For example, a PATHOBJ can hold all the extra data required to enumerate a complex object like a path.

The following user objects are available:

BRUSHOBJ

Defines the brush objects for graphic functions that output lines, text, or fills. Drivers can call BRUSHOBJ services to realize brushes or to find realizations previously cached by GDI.

CLIPOBJ

Provides the driver with access to a clip region for drawing or filling. This region can be enumerated as a series of rectangles.

FLOATOBJ

Allows graphics drivers to emulate floating point operations. Floating point operations are disabled for all other kernel-mode drivers.

FONTOBJ

Gives the driver access to information about a particular instance (or realization) of a font.

PALOBJ

A structure containing RGB palette colors; accessible via the PALOBJ_cGetColors and DrvSetPalette functions.

PATHOBJ

Defines a path that specifies what is to be drawn (lines or Bezier curves). PATHOBJ is passed to the driver to describe a set of lines and Bezier curves that are to be stroked or filled.

STROBJ

Enumerates a list of glyph handles and positions for the driver that describes how a text string is to be drawn.

SURFOBJ

Identifies a surface, which can be a GDI bitmap, a device-dependent bitmap, or a device-managed surface.

XFORMOBJ

Describes an arbitrary linear two-dimensional transform, such as for geometric wide lines.

XLATEOBJ

Translates color indexes that refer to a source palette into indexes for a destination palette. The resulting destination indexes identify colors that match the surface color as closely as possible.

BRUSHOBJ	Defines the brush objects for graphic functions that output lines, text, or fills. Drivers can call BRUSHOBJ services to realize brushes or to find realizations previously cached by GDI.
CLIPOBJ	Provides the driver with access to a clip region for drawing or filling. This region can be enumerated as a series of rectangles.
FLOATOBJ	Allows graphics drivers to emulate floating point operations. Floating point operations are disabled for all other kernel-mode drivers.
FONTOBJ	Gives the driver access to information about a particular instance (or realization) of a font.
PALOBJ	A structure containing RGB palette colors; accessible via the PALOBJ_cGetColors and DrvSetPalette functions.
PATHOBJ	Defines a path that specifies what is to be drawn (lines or Bezier curves). PATHOBJ is passed to the driver to describe a set of lines and Bezier curves that are to be stroked or filled.
STROBJ	Enumerates a list of glyph handles and positions for the driver that describes how a text string is to be drawn.
SURFOBJ	Identifies a surface, which can be a GDI bitmap, a device-dependent bitmap, or a device-managed surface.
XFORMOBJ	Describes an arbitrary linear two-dimensional transform, such as for geometric wide lines.
XLATEOBJ	Translates color indexes that refer to a source palette into indexes for a destination palette. The resulting destination indexes identify colors that match the surface color as closely as possible.