窗口回调函数

/*
WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
和
typedef struct tagMSG {
HWND hwnd;
UINT message;
WPARAM wParam;
LPARAM lParam;
DWORD time;
POINT pt;
} MSG, *PMSG;

　　　　　//此处分发消息，调用消息回调函数，
        //同时消息回调函数的返回值作为DIspatchMessage的返回值返回，
        //一般讲这个返回值忽略
        DispatchMessage(&msg);
        /*
        The return value specifies the value returned by the window procedure. Although its meaning depends on the message being dispatched, the return value generally is ignored. 
        返回值指定窗口过程返回的值。尽管它的含义依赖于发送的消息，但是返回值通常被忽略。
        */