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 and GetObject 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 and EnumFontFamilies. 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.

Graphic object	Function
Bitmap	CreateBitmap, CreateBitmapIndirect, CreateCompatibleBitmap, CreateDiscardableBitmap, CreateDIBitmap
Brush	CreateBrushIndirect, CreateDIBPatternBrush, CreateDIBPatternBrushPt, CreateHatchBrush, CreatePatternBrush, CreateSolidBrush
Color Palette	CreatePalette
Font	CreateFont, CreateFontIndirect
Pen	CreatePen, CreatePenIndirect, ExtCreatePen
Region	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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