获取窗口最大化区域

void CMainFrame::GetFullViewRect(RECT &rt)
{
    rt.left=0;
    rt.right=800;
    rt.top=0;
    rt.bottom=600;
    HWND hwnd1=0,hwnd2=0;
    hwnd1=::GetDesktopWindow();
    if(hwnd1==NULL) return;

    RECT rt_Desktop;
    ::GetWindowRect(hwnd1,&rt_Desktop);
    
    hwnd2=::FindWindow("Shell_TrayWnd",NULL);
    if(hwnd2==NULL) return;

    RECT rt_TrayWnd;
    ::GetWindowRect(hwnd2,&rt_TrayWnd);
    if((rt_TrayWnd.bottom-rt_TrayWnd.top)<(rt_TrayWnd.right-rt_TrayWnd.left))
    {
        if((rt_Desktop.bottom-rt_TrayWnd.bottom)>0)
        {
            rt.top = rt_TrayWnd.bottom;
            rt.left = rt_Desktop.left;
            rt.bottom = rt_Desktop.bottom;
            rt.right = rt_Desktop.right;
        }
        else
        {
            rt.top = rt_Desktop.top;
            rt.left = rt_Desktop.left;
            rt.bottom = rt_TrayWnd.top;
            rt.right = rt_Desktop.right;
        }
    }
    else
    {
        if((rt_Desktop.right-rt_TrayWnd.right)>0)
        {
            rt.top = rt_Desktop.top;
            rt.left = rt_TrayWnd.right;
            rt.bottom = rt_Desktop.bottom;
            rt.right = rt_Desktop.right;
        }
        else
        {
            rt.top = rt_Desktop.top;
            rt.left = rt_Desktop.left;
            rt.bottom = rt_Desktop.bottom;
            rt.right = rt_TrayWnd.left;
        }
    }

    if((rt.right-rt.left)<800) rt.right=rt.left+800;
    if((rt.bottom-rt.top)<600) rt.bottom=rt.top+600;
}