This function is a library-defined callback function that serves as the entry point for a Control Panel application.
LONG CPlApplet( HWND hwndCPl, UINT msg, LPARAM lParam1, LPARAM lParam2 );
[in] Handle to the main window of the controlling application. Use the hwndCPl parameter for other applications or windows that require a handle to a parent window.
[in] Message being sent to the Control Panel application.
[in] Additional message-specific information.
[in] Additional message-specific information
The return value depends on the message.
The CPlApplet function is an application-defined callback function that serves as the entry point for a Control Panel application. The APPLET_PROC type defines a pointer to this callback function.
When the Control Panel starts, it loads all DLL files that have a .cpl file name extension (such as MyApplet.cpl) in the Windows folder. The Control Panel calls the CPlApplet function that was implemented and exported in each CPL file. The CPlApplet function must properly handle any of the control panel messages that are sent to it programmatically or via calls from the Control Panel.
If more than one Control Panel application is implemented in a .cpl file, a single CPlApplet function is used for all of the Control Panel applications.