An application sends the WM_SETREDRAW message to a window to allow changes in that window to be redrawn or to prevent changes in that window from being redrawn.
WM_SETREDRAW wParam = (WPARAM) fRedraw; // state of redraw flag lParam = 0; // not used; must be zero
An application should return zero if it processes this message.
This message sets or clears the redraw flag. If the redraw flag is cleared, the content of the given window is not updated after each change, and the window is not repainted until the redraw flag is set. For example, an application that must add several items to a list box can clear the redraw flag, add the items, and then set the redraw flag. Finally, the application can call the InvalidateRect function to cause the list box to be repainted.