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You can retrieve a pointer to a surface's IDirectDrawSurface5interface from the device context for the surface by calling the IDirectDraw4::GetSurfaceFromDCmethod. This feature might be very useful for component applications or ActiveX controls, that are commonly given a device context to draw into at run-time, but could benefit by exploiting the features exposed by the IDirectDrawSurface5interface.
A device context might identify memory that isn't associated with a DirectDraw object, or the device context might identify a surface for another DirectDraw object entirely. The latter case is most likely to occur on a system with multiple monitors. If the device context doesn't identify a surface that wasn't created by that DirectDraw object, the method fails, returning DDERR_NOTFOUND.
The following sample code shows what a very simple scenario might look like:
// For this example, the hdc variable is a valid
// handle to a video memory device context, and the // lpDD4
variable is a valid IDirectDraw4 interface pointer.
LPDIRECTDRAWSURFACE4 lpDDS4; HRESULT hr; hr =
lpDD4->GetSurfaceFromDC(hdc, &lpDDS4); if(SUCCEEDED(hr)) {
// Use the surface interface. } else if(DDERR_NOTFOUND == hr) {
OutputDebugString("HDC not from this DirectDraw surface\n");
}
Last updated on Tuesday, May 18, 2004