Friday, February 22, 2013

WM_PAINT


WM_PAINT:
Windows call various events by sending message (arguments) in the application message queue or sending message to the appropriate window procedure. Window procedure paints the window by sending message WM_PAINT message.

The WM_PAINT message:
The windows program calls the Update Window before entering the message loop. Windows procedure takes it as first WM_PAINT message. This message informs the window procedure that the client area must be painted or updated. Thereafter the windows procedure should be ready to repaint the window if necessary.
A window procedure receives a WM_PAINT message whenever following event occurs:-
1.     The user re-sizes the window.
2.     The client area is scrolled. (Scrolled Window)
3.     Previously hidden area of the window is brought into view. (Uncover Window)

In few cases windows always save an area of display, it overwrites and restores it when –
1.     Mouse cursor is moved across the client control area.
2.     An icon is dragged across the client area.

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