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Dragging a window by its client area

The simplest way to drag a window by its client area (or drag a window if it has no title bar), is to handle the WM_NCHITTEST message that is sent to every window when a mouse event occurs.
By returning a value of HTCAPTION from the WM_NCHITTEST message handler, you can fool windows into thinking that the mouse is over a caption bar, and the window can be dragged around with the mouse. It is best to only allow dragging by the client area of a window - otherwise, the window borders would become unusable. To achieve this, call the default window procedure, and check if its return value is HTCLIENT - if it is, then return HTCAPTION instead. Otherwise, just let the default behaviour take place.

UINT uHitTest;...case WM_NCHITTEST:    uHitTest = DefWindowProc(hwnd, WM_NCHITTEST, wParam, lParam);    if(uHitTest == HTCLIENT)        return HTCAPTION;    else        return uHitTest;