二个问题，VC,SetWindowsHook,及......Hep~~

（一）:
HHOOK MyHook;
CMouse_testApp theApp;
LRESULT CALLBACK MyMouseHook(
int nCode, // hook code
WPARAM wParam, // message identifier
LPARAM lParam // mouse coordinates
)
{
if(nCode>=0)
{
if(wParam==WM_LBUTTONDOWN)
{
::MessageBox(0,"点击事件","",0);///1、这钩子下完后，单击一次窗体怎么会响应多次？
///这是为什么？而响应多次后，又不响应了，晕~~~，
///2、还有一点，为什么只在本窗体单击有效，我想要整个
///桌面都有效的怎么做？？
Beep(2000,55);
}
}
return ::CallNextHookEx(MyHook,nCode,wParam,lParam );
}

void CMouse_testDlg::OnLButtonDblClk(UINT nFlags, CPoint point)
{
// TODO: Add your message handler code here and/or call default
if( MyHook)
{
::UnhookWindowsHookEx(MyHook);
MyHook=NULL;
}
else
{
MyHook=::SetWindowsHookEx(WH_MOUSE,(HOOKPROC)MyMouseHook,theApp.m_hInstance,0);
}
CDialog::OnLButtonDblClk(nFlags, point);
}


（二）：
void CMouse_testDlg::OnMouseMove(UINT nFlags, CPoint point)
{
// TODO: Add your message handler code here and/or call default
ClientToScreen(&point);
m_Pos.Format("x=%d,y=%d",point.x,point.y);
m_color=::GetPixel(::GetDC(0),point.x,point.y);///1、这个函数怎么就对本窗体才能获得RGB值，
///而把鼠标移开后本窗体后
///如：鼠标在桌面上或别的应用程序上，
///就不能获得RGB值了，这为什么？
///要怎么做才能获取全局鼠标的RGB值啊。555555
//InvalidateRect(lRect,true);

m_RGB.Format("RGB(R=%d,G=%d,B=%d)",GetRValue(m_color),GetGValue(m_color),GetBValue(m_color));
AfxGetMainWnd()->SetWindowText(m_RGB);//标题
UpdateData(FALSE);
CDialog::OnMouseMove(nFlags, point);
}

help~.....