Operations on Graphic Objects
Once an application creates a display or printer device context, it can begin
drawing on the associated device or, in the case of the memory device context,
it can begin drawing on the bitmap stored in memory. However, before drawing
begins and sometimes while drawing is in progress, it is often necessary to
replace the default objects with new objects.
An application can examine a default object's attributes by calling the GetCurrentObject
functions. The GetCurrentObject
function returns a handle identifying the current pen, brush, palette,
bitmap, or font, and the GetObject
function initializes a structure containing that object's attributes.
Some printers provide resident pens, brushes, and fonts that can be used to
improve drawing speed in an application. Two functions can be used to enumerate
these objects: EnumObjects
. If the application must enumerate resident pens or brushes, it can call the EnumObjects
function to examine the corresponding attributes. If the application must
enumerate resident fonts, it can call the EnumFontFamilies
function (which can also enumerate GDI fonts).
Once an application determines that a default object needs replacing, it
creates a new object by calling one of the following creation functions.
||CreateBitmap, CreateBitmapIndirect, CreateCompatibleBitmap, CreateDiscardableBitmap, CreateDIBitmap
||CreateBrushIndirect, CreateDIBPatternBrush, CreateDIBPatternBrushPt, CreateHatchBrush, CreatePatternBrush, CreateSolidBrush
||CreatePen, CreatePenIndirect, ExtCreatePen
||CreateEllipticRgn, CreateEllipticRgnIndirect, CreatePolygonRgn, CreatePolyPolygonRgn, CreateRectRgn, CreateRectRgnIndirect, CreateRoundRectRgn
Each of these functions returns a handle identifying a new object. After an
application retrieves a handle, it must call the SelectObject
function to replace the default object. However, the application should save
the handle identifying the default object and use this handle to replace the
new object when it is no longer needed. When the application finishes drawing
with the new object, it must restore the default object by calling the SelectObject
function and delete the new object by calling the DeleteObject
function. Failing to delete objects causes serious performance problems.
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