In DirectDraw7/Direct3D7:

[pascal][background=#FFFFFF][normal=#000000][number=#0000FF][string=#0000FF][comment=#248F24][reserved=#000000](1) at init time:
if (ddObject.CreateClipper(0, @ddClipper, NULL) = DD_OK) then
ddClipper.SetHWnd(0, hwndAppWindow);
ddObject.FlipToGDISurface;

(2) later
ddFrontBuffer.SetClipper(ddClipper);
ddFrontBuffer.Blt(NULL, ddBackBuffer, NULL, DDBLT_WAIT, NULL);
// or Flip
ddObject.FlipToGDISurface;[/pascal]