The CallWindowProc function passes message information to the specified window procedure. LRESULT CallWindowProc( WNDPROC lpPrevWndFunc, // pointer to previous procedure
HWND hWnd, // handle to window
UINT Msg, // message
WPARAM wParam, // first message parameter
LPARAM lParam // second message parameter
);
ParameterslpPrevWndFuncPointer to the previous window procedure.
If this value is obtained by calling the GetWindowLong function with the nIndex parameter set to GWL_WNDPROC or DWL_DLGPROC, it is actually either the address of a window or dialog box procedure, or a handle representing that address.hWndIdentifies the window procedure to receive the message. MsgSpecifies the message. wParamSpecifies additional message-specific information. The contents of this parameter depend on the value of the Msg parameter.lParamSpecifies additional message-specific information. The contents of this parameter depend on the value of the Msg parameter. Return ValuesThe return value specifies the result of the message processing and depends on the message sent. ResUse the CallWindowProc function for window subclassing. Usually, all windows with the same class share one window procedure. A subclass is a window or set of windows with the same class whose messages are intercepted and processed by another window procedure (or procedures) before being passed to the window procedure of the class.
The SetWindowLong function creates the subclass by changing the window procedure associated with a particular window, causing Windows to call the new window procedure instead of the previous one. An application must pass any messages not processed by the new window procedure to the previous window procedure by calling CallWindowProc. This allows the application to create a chain of window procedures. If STRICT is defined, the lpPrevWndFunc parameter has the data type WNDPROC. The WNDPROC type is declared as follows: LRESULT (CALLBACK* WNDPROC) (HWND, UINT, WPARAM, LPARAM);
If STRICT is not defined, the lpPrevWndFunc parameter has the data type FARPROC. The FARPROC type is declared as follows: int (FAR WINAPI * FARPROC) ()
In C, the FARPROC declaration indicates a callback function that has an unspecified parameter list. In C++, however, the empty parameter list in the declaration indicates that a function has no parameters. This subtle distinction can break careless code. Following is one way to handle this situation: #ifdef STRICT
WNDPROC MyWindowProcedure
#else
FARPROC MyWindowProcedure
#endif
...
lResult = CallWindowProc(MyWindowProcedure, ...) ;
For further information about functions declared with empty argument lists, refer to The C++ Programming Language, Second Edition, by Bjarne Stroustrup.
Windows NT: The CallWindowProc function handles Unicode-to-ANSI conversion. You don't get the conversion if you call the window procedure directly.
HWND hWnd, // handle to window
UINT Msg, // message
WPARAM wParam, // first message parameter
LPARAM lParam // second message parameter
);
ParameterslpPrevWndFuncPointer to the previous window procedure.
If this value is obtained by calling the GetWindowLong function with the nIndex parameter set to GWL_WNDPROC or DWL_DLGPROC, it is actually either the address of a window or dialog box procedure, or a handle representing that address.hWndIdentifies the window procedure to receive the message. MsgSpecifies the message. wParamSpecifies additional message-specific information. The contents of this parameter depend on the value of the Msg parameter.lParamSpecifies additional message-specific information. The contents of this parameter depend on the value of the Msg parameter. Return ValuesThe return value specifies the result of the message processing and depends on the message sent. ResUse the CallWindowProc function for window subclassing. Usually, all windows with the same class share one window procedure. A subclass is a window or set of windows with the same class whose messages are intercepted and processed by another window procedure (or procedures) before being passed to the window procedure of the class.
The SetWindowLong function creates the subclass by changing the window procedure associated with a particular window, causing Windows to call the new window procedure instead of the previous one. An application must pass any messages not processed by the new window procedure to the previous window procedure by calling CallWindowProc. This allows the application to create a chain of window procedures. If STRICT is defined, the lpPrevWndFunc parameter has the data type WNDPROC. The WNDPROC type is declared as follows: LRESULT (CALLBACK* WNDPROC) (HWND, UINT, WPARAM, LPARAM);
If STRICT is not defined, the lpPrevWndFunc parameter has the data type FARPROC. The FARPROC type is declared as follows: int (FAR WINAPI * FARPROC) ()
In C, the FARPROC declaration indicates a callback function that has an unspecified parameter list. In C++, however, the empty parameter list in the declaration indicates that a function has no parameters. This subtle distinction can break careless code. Following is one way to handle this situation: #ifdef STRICT
WNDPROC MyWindowProcedure
#else
FARPROC MyWindowProcedure
#endif
...
lResult = CallWindowProc(MyWindowProcedure, ...) ;
For further information about functions declared with empty argument lists, refer to The C++ Programming Language, Second Edition, by Bjarne Stroustrup.
Windows NT: The CallWindowProc function handles Unicode-to-ANSI conversion. You don't get the conversion if you call the window procedure directly.
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int nXDest, // x-coordinate of destination rectangle's upper-left corner
int nYDest, // y-coordinate of destination rectangle's upper-left corner
int nWidth, // width of destination rectangle
int nHeight, // height of destination rectangle
HDC hdcSrc, // handle to source device context
int nXSrc, // x-coordinate of source rectangle's upper-left corner
int nYSrc, // y-coordinate of source rectangle's upper-left corner
DWORD dwRop // raster operation code
);
ParametershdcDestIdentifies the destination device context. nXDestSpecifies the logical x-coordinate of the upper-left corner of the destination rectangle.nYDestSpecifies the logical y-coordinate of the upper-left corner of the destination rectangle. nWidthSpecifies the logical width of the source and destination rectangles. nHeightSpecifies the logical height of the source and the destination rectangles. hdcSrcIdentifies the source device context. nXSrcSpecifies the logical x-coordinate of the upper-left corner of the source rectangle. nYSrcSpecifies the logical y-coordinate of the upper-left corner of the source rectangle. dwRopSpecifies a raster-operation code. These codes define how the color data for the source rectangle is to be combined with the color data for the destination rectangle to achieve the final color.
The following list shows some common raster operation codes: Value Description
BLACKNESS Fills the destination rectangle using the color associated with index 0 in the physical palette. (This color is black for the default physical palette.)
DSTINVERT Inverts the destination rectangle.
MERGECOPY Merges the colors of the source rectangle with the specified pattern by using the Boolean AND operator.
MERGEPAINT Merges the colors of the inverted source rectangle with the colors of the destination rectangle by using the Boolean OR operator.
NOTSRCCOPY Copies the inverted source rectangle to the destination.
NOTSRCERASE Combines the colors of the source and destination rectangles by using the Boolean OR operator and then inverts the resultant color.
PATCOPY Copies the specified pattern into the destination bitmap.
PATINVERT Combines the colors of the specified pattern with the colors of the destination rectangle by using the Boolean XOR operator.
PATPAINT Combines the colors of the pattern with the colors of the inverted source rectangle by using the Boolean OR operator. The result of this operation is combined with the colors of the destination rectangle by using the Boolean OR operator.
SRCAND Combines the colors of the source and destination rectangles by using the Boolean AND operator.
SRCCOPY Copies the source rectangle directly to the destination rectangle.
SRCERASE Combines the inverted colors of the destination rectangle with the colors of the source rectangle by using the Boolean AND operator.
SRCINVERT Combines the colors of the source and destination rectangles by using the Boolean XOR operator.
SRCPAINT Combines the colors of the source and destination rectangles by using the Boolean OR operator.
WHITENESS Fills the destination rectangle using the color associated with index 1 in the physical palette. (This color is white for the default physical palette.)
Return ValuesIf the function succeeds, the return value is nonzero.
If the function fails, the return value is zero. To get extended error information, call GetLastError. ResIf a rotation or shear transformation is in effect in the source device context, BitBlt returns an error. If other transformations exist in the source device context (and a matching transformation is not in effect in the destination device context), the rectangle in the destination device context is stretched, compressed, or rotated as necessary.
If the color formats of the source and destination device contexts do not match, the BitBlt function converts the source color format to match the destination format. When an enhanced metafile is being recorded, an error occurs if the source device context identifies an enhanced-metafile device context.
Not all devices support the BitBlt function. For more information, see the RC_BITBLT raster capability entry in GetDeviceCaps.
BitBlt returns an error if the source and destination device contexts represent different devices.
int nXDest, // x-coordinate of destination rectangle's upper-left corner
int nYDest, // y-coordinate of destination rectangle's upper-left corner
int nWidth, // width of destination rectangle
int nHeight, // height of destination rectangle
HDC hdcSrc, // handle to source device context
int nXSrc, // x-coordinate of source rectangle's upper-left corner
int nYSrc, // y-coordinate of source rectangle's upper-left corner
DWORD dwRop // raster operation code
);
ParametershdcDestIdentifies the destination device context. nXDestSpecifies the logical x-coordinate of the upper-left corner of the destination rectangle.nYDestSpecifies the logical y-coordinate of the upper-left corner of the destination rectangle. nWidthSpecifies the logical width of the source and destination rectangles. nHeightSpecifies the logical height of the source and the destination rectangles. hdcSrcIdentifies the source device context. nXSrcSpecifies the logical x-coordinate of the upper-left corner of the source rectangle. nYSrcSpecifies the logical y-coordinate of the upper-left corner of the source rectangle. dwRopSpecifies a raster-operation code. These codes define how the color data for the source rectangle is to be combined with the color data for the destination rectangle to achieve the final color.
The following list shows some common raster operation codes: Value Description
BLACKNESS Fills the destination rectangle using the color associated with index 0 in the physical palette. (This color is black for the default physical palette.)
DSTINVERT Inverts the destination rectangle.
MERGECOPY Merges the colors of the source rectangle with the specified pattern by using the Boolean AND operator.
MERGEPAINT Merges the colors of the inverted source rectangle with the colors of the destination rectangle by using the Boolean OR operator.
NOTSRCCOPY Copies the inverted source rectangle to the destination.
NOTSRCERASE Combines the colors of the source and destination rectangles by using the Boolean OR operator and then inverts the resultant color.
PATCOPY Copies the specified pattern into the destination bitmap.
PATINVERT Combines the colors of the specified pattern with the colors of the destination rectangle by using the Boolean XOR operator.
PATPAINT Combines the colors of the pattern with the colors of the inverted source rectangle by using the Boolean OR operator. The result of this operation is combined with the colors of the destination rectangle by using the Boolean OR operator.
SRCAND Combines the colors of the source and destination rectangles by using the Boolean AND operator.
SRCCOPY Copies the source rectangle directly to the destination rectangle.
SRCERASE Combines the inverted colors of the destination rectangle with the colors of the source rectangle by using the Boolean AND operator.
SRCINVERT Combines the colors of the source and destination rectangles by using the Boolean XOR operator.
SRCPAINT Combines the colors of the source and destination rectangles by using the Boolean OR operator.
WHITENESS Fills the destination rectangle using the color associated with index 1 in the physical palette. (This color is white for the default physical palette.)
Return ValuesIf the function succeeds, the return value is nonzero.
If the function fails, the return value is zero. To get extended error information, call GetLastError. ResIf a rotation or shear transformation is in effect in the source device context, BitBlt returns an error. If other transformations exist in the source device context (and a matching transformation is not in effect in the destination device context), the rectangle in the destination device context is stretched, compressed, or rotated as necessary.
If the color formats of the source and destination device contexts do not match, the BitBlt function converts the source color format to match the destination format. When an enhanced metafile is being recorded, an error occurs if the source device context identifies an enhanced-metafile device context.
Not all devices support the BitBlt function. For more information, see the RC_BITBLT raster capability entry in GetDeviceCaps.
BitBlt returns an error if the source and destination device contexts represent different devices.