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Drawing control on memory device context

galkin
galkin asked
on
Medium Priority
680 Views
Last Modified: 2013-11-20
I need control( for example button) to draw itself on memory device context.
I created this device context and call ::SendMessage(hwndControl, WM_PAINT,
(WPARAM)memDC.GetSafeHdc(), 0). The problem is that in this case invalid
rectangle is empty and control doesn't paint itself. If I specify
InvalidateRect(NULL) before sending message then control does paint itself
on memory DC but it also paints itself on window DC. I also tried to call
ValidateRect(NULL) just after sending message but it doesn't help. How can I
force control to draw itself on memory DC only?
            Thanks.
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Commented:
Send WM_PRINT message instead of WM_PAINT.

WM_PRINT
The WM_PRINT message is sent to a window to request that it draw itself in the specified device context, most commonly in a printer device context.

WM_PRINT
hdc = (HDC) wParam;
uFlags = lParam;
 
Parameters
hdc
Identifies the device context to draw in.

uFlags
Specifies the drawing options. This parameter can be one or more of these flags:Value Meaning
PRF_CHECKVISIBLE Draw the window only if it is visible.
PRF_CHILDREN Draw all visible children windows.
PRF_CLIENT Draw the client area of the window.
PRF_ERASEBKGND Erase the background before drawing the window.
PRF_NONCLIENT Draw the nonclient area of the window.
PRF_OWNED Draw all owned windows.


Remarks
The DefWindowProc function processes this message based on which drawing option is specified: if PRF_CHECKVISIBLE is specified and the window is not visible, do nothing, if PRF_NONCLIENT is specified, draw the nonclient area in the given device context, if PRF_ERASEBKGND is specified, send the window a WM_ERASEBKGND message, if PRF_PRINTCLIENT is specified, send the window a WM_PRINTCLIENT message, if PRF_PRINTCHILDREN is set, send each visible child window a WM_PRINT message, if PRF_OWNED is set, send each visible owned window a WM_PRINT message.

QuickInfo
  Windows NT: Use version 4.0 and later.
  Windows: Use Windows 95 and later.
  Header: Declared in winuser.h.

See Also
Painting and Drawing Overview, Painting and Drawing Messages, DefWindowProc, WM_ERASEBKGND, WM_PRINTCLIENT

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