Invalidating and Validating the Update Region
An application invalidates a portion of a window and sets the update region by
using the
InvalidateRect or
InvalidateRgn function. These functions add the specified rectangle or region (given in
client coordinates) to the update region, combining the rectangle or region with
anything Windows or the application may have previously added to the update
region.
The
InvalidateRect and
InvalidateRgn functions do not generate
WM_PAINT messages. Instead, Windows accumulates the changes made by these functions
and its own changes while a window processes other messages in its message queue.
By accumulating changes, a window processes all changes at once instead of
updating bits and pieces one step at a time.
The
ValidateRect and
ValidateRgn functions validate a portion of the window by removing a specified rectangle
or region from the update region. These functions are typically used when the
window has updated a specific part of the screen in the update region before
receiving the WM_PAINT message.
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