(Win32) Window Framework

LRESULT CALLBACK Window::HandleMsgSetup( HWND hWnd,UINT msg,WPARAM wParam,LPARAM lParam ) noexcept
{
	// use create parameter passed in from CreateWindow() to store window class pointer at WinAPI side
	if( msg == WM_NCCREATE )
	{
		// extract ptr to window class from creation data
		const CREATESTRUCTW* const pCreate = reinterpret_cast<CREATESTRUCTW*>(lParam);
		Window* const pWnd = static_cast<Window*>(pCreate->lpCreateParams);
		// set WinAPI-managed user data to store ptr to window class
        // GWLP_USERDATA유저 데이터를 win32내에 저장할수 있는데 핸들값을 저장해둠
		SetWindowLongPtr( hWnd,GWLP_USERDATA,reinterpret_cast<LONG_PTR>(pWnd) );
		// set message proc to normal (non-setup) handler now that setup is finished
        // 메시지 처리를 Window::HandleMsgThunk에 넘기게 된다.
		SetWindowLongPtr( hWnd,GWLP_WNDPROC,reinterpret_cast<LONG_PTR>(&Window::HandleMsgThunk) );
		// forward message to window class handler
		return pWnd->HandleMsg( hWnd,msg,wParam,lParam );
	}
	// if we get a message before the WM_NCCREATE message, handle with default handler
	return DefWindowProc( hWnd,msg,wParam,lParam );
}

// 이제 메시지 처리는 HandleMsgThunk가 한다
LRESULT CALLBACK Window::HandleMsgThunk( HWND hWnd,UINT msg,WPARAM wParam,LPARAM lParam ) noexcept
{
	// retrieve ptr to window class
	Window* const pWnd = reinterpret_cast<Window*>(GetWindowLongPtr( hWnd,GWLP_USERDATA ));
	// forward message to window class handler
	return pWnd->HandleMsg( hWnd,msg,wParam,lParam );
}

LRESULT Window::HandleMsg( HWND hWnd,UINT msg,WPARAM wParam,LPARAM lParam ) noexcept
{
	switch( msg )
	{
	// we don't want the DefProc to handle this message because
	// we want our destructor to destroy the window, so return 0 instead of break
	case WM_CLOSE:
		PostQuitMessage( 0 );
		return 0;
	}

	return DefWindowProc( hWnd,msg,wParam,lParam );
}