The runtime updates the window client area immediately and might do so more than once during the adapter refresh period. This is equivalent to using D3DSWAPEFFECT_COPY in DirectX 8.0. IDirect3DDevice9:resent operations might be affected immediately. This option is always available for both windowed and full-screen swap chains.
楼主
resent operations might be affected immediately. This option is always available for both windowed and full-screen swap chains.