GetDCEx function

The GetDCEx function retrieves a handle to a device context (DC) for the client area of a specified window or for the entire screen. You can use the returned handle in subsequent GDI functions to draw in the DC. The device context is an opaque data structure, whose values are used internally by GDI.

This function is an extension to the GetDC function, which gives an application more control over how and whether clipping occurs in the client area.

Syntax

HDC GetDCEx(
  HWND  hWnd,
  HRGN  hrgnClip,
  DWORD flags
);

Parameters

hWnd

A handle to the window whose DC is to be retrieved. If this value is NULL, GetDCEx retrieves the DC for the entire screen.

hrgnClip

A clipping region that may be combined with the visible region of the DC. If the value of flags is DCX_INTERSECTRGN or DCX_EXCLUDERGN, then the operating system assumes ownership of the region and will automatically delete it when it is no longer needed. In this case, the application should not use or delete the region after a successful call to GetDCEx.

flags

Specifies how the DC is created. This parameter can be one or more of the following values.

Value Meaning
DCX_WINDOW
Returns a DC that corresponds to the window rectangle rather than the client rectangle.
DCX_CACHE
Returns a DC from the cache, rather than the OWNDC or CLASSDC window. Essentially overrides CS_OWNDC and CS_CLASSDC.
DCX_PARENTCLIP
Uses the visible region of the parent window. The parent's WS_CLIPCHILDREN and CS_PARENTDC style bits are ignored. The origin is set to the upper-left corner of the window identified by hWnd.
DCX_CLIPSIBLINGS
Excludes the visible regions of all sibling windows above the window identified by hWnd.
DCX_CLIPCHILDREN
Excludes the visible regions of all child windows below the window identified by hWnd.
DCX_NORESETATTRS
This flag is ignored.
DCX_LOCKWINDOWUPDATE
Allows drawing even if there is a LockWindowUpdate call in effect that would otherwise exclude this window. Used for drawing during tracking.
DCX_EXCLUDERGN
The clipping region identified by hrgnClip is excluded from the visible region of the returned DC.
DCX_INTERSECTRGN
The clipping region identified by hrgnClip is intersected with the visible region of the returned DC.
DCX_INTERSECTUPDATE
Reserved; do not use.
DCX_VALIDATE
Reserved; do not use.

Return Value

If the function succeeds, the return value is the handle to the DC for the specified window.

If the function fails, the return value is NULL. An invalid value for the hWnd parameter will cause the function to fail.

Remarks

Unless the display DC belongs to a window class, the ReleaseDC function must be called to release the DC after painting. Also, ReleaseDC must be called from the same thread that called GetDCEx. The number of DCs is limited only by available memory.

The function returns a handle to a DC that belongs to the window's class if CS_CLASSDC, CS_OWNDC or CS_PARENTDC was specified as a style in the WNDCLASS structure when the class was registered.

Requirements

   
Minimum supported client Windows 2000 Professional [desktop apps only]
Minimum supported server Windows 2000 Server [desktop apps only]
Target Platform Windows
Header winuser.h (include Windows.h)
Library User32.lib
DLL User32.dll

See Also

BeginPaint

Device Context Functions

Device Contexts Overview

GetWindowDC

ReleaseDC

WNDCLASS