Combines the color data for the source and destination bitmaps using the given mask and raster operation.
BOOL MaskBlt( int x, int y, int nWidth, int nHeight, CDC* pSrcDC, int xSrc, int ySrc, CBitmap& maskBitmap, int xMask, int yMask, DWORD dwRop );
A value of 1 in the mask specified by maskBitmap indicates that the foreground raster operation code specified by dwRop should be applied at that location. A value of 0 in the mask indicates that the background raster operation code specified by dwRop should be applied at that location. If the raster operations require a source, the mask rectangle must cover the source rectangle. If it does not, the function will fail. If the raster operations do not require a source, the mask rectangle must cover the destination rectangle. If it does not, the function will fail.
If a rotation or shear transformation is in effect for the source device context when this function is called, an error occurs. However, other types of transformations are allowed.
If the color formats of the source, pattern, and destination bitmaps differ, this function converts the pattern or source format, or both, to match the destination format. If the mask bitmap is not a monochrome bitmap, an error occurs. When an enhanced metafile is being recorded, an error occurs (and the function returns 0) if the source device context identifies an enhanced-metafile device context. Not all devices support MaskBlt. An application should call GetDeviceCaps to determine whether a device supports this function. If no mask bitmap is supplied, this function behaves exactly like BitBlt, using the foreground raster operation code. The pixel offsets in the mask bitmap map to the point (0,0) in the source device context's bitmap. This is useful for cases in which a mask bitmap contains a set of masks; an application can easily apply any one of them to a mask-blitting task by adjusting the pixel offsets and rectangle sizes sent to MaskBlt.