L_BN_CHANGE

When received, this message indicates that the user has taken an action that may have altered the bitmap. For example, flipping or rotating the bitmap would cause this message to be sent.

It is sent after Windows updates a display (unlike the L_BN_UPDATE code.) The L_BITMAPCLASS window's parent window receives this code through a WM_COMMAND message from the L_BITMAPCLASS window.

Parameter	Description
wParam	Contains the wParam parameter of the WM_COMMAND message and specifies the child-window ID.
lParam	Contains the L_BITMAPCLASS windows handle in its low-order word and the L_BN_CHANGE code in its high-order word.