InvalidateRgn

The InvalidateRgn function invalidates the client area within the specified region by adding it to the current update region of a window. The invalidated region, along with all other areas in the update region, is marked for painting when the next WM_PAINT message occurs.

BOOL InvalidateRgn(

HWND hWnd,	// handle of window with changed update region
HRGN hRgn,	// handle of region to add
BOOL bErase	// erase-background flag
);

Parameters

hWnd

Identifies the window with an update region that is to be modified.

hRgn

Identifies the region to be added to the update region. The region is assumed to have client coordinates. If this parameter is NULL, the entire client area is added to the update region.

bErase

Specifies whether the background within the update region should be erased when the update region is processed. If this parameter is TRUE, the background is erased when the BeginPaint function is called. If the parameter is FALSE, the background remains unchanged.

Return Values

The return value is always nonzero.

Remarks

Invalidated areas accumulate in the update region until the next WM_PAINT message is processed or until the region is validated by using the ValidateRect or ValidateRgn function.

Windows sends a WM_PAINT message to a window whenever its update region is not empty and there are no other messages in the application queue for that window.

The specified region must have been created by using one of the region functions.

If the bErase parameter is TRUE for any part of the update region, the background in the entire region is erased, not just in the specified part.

See Also

BeginPaint, InvalidateRect, ValidateRect, ValidateRgn, WM_PAINT

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