Sent to a window when its nonclient area needs to be changed to indicate an active or inactive state.
A window receives this message through its WindowProc function.
Indicates when a title bar or icon needs to be changed to indicate an active or inactive state. If an active title bar or icon is to be drawn, the wParam parameter is TRUE. If an inactive title bar or icon is to be drawn, wParam is FALSE.
When a visual style is active for this window, this parameter is not used.
When a visual style is not active for this window, this parameter is a handle to an optional update region for the nonclient area of the window. If this parameter is set to -1, DefWindowProc does not repaint the nonclient area to reflect the state change.
When the wParam parameter is FALSE, an application should return TRUE to indicate that the system should proceed with the default processing, or it should return FALSE to prevent the change. When wParam is TRUE, the return value is ignored.
Processing messages related to the nonclient area of a standard window is not recommended, because the application must be able to draw all the required parts of the nonclient area for the window. If an application does process this message, it must return TRUE to direct the system to complete the change of active window. If the window is minimized when this message is received, the application should pass the message to the DefWindowProc function.
The DefWindowProc function draws the title bar or icon title in its active colors when the wParam parameter is TRUE and in its inactive colors when wParam is FALSE.
Minimum supported client
|Windows 2000 Professional [desktop apps only]|
Minimum supported server
|Windows 2000 Server [desktop apps only]|