Digital Clock in Windows Programming

I feel that this clock, in addition to some mathematical knowledge, is still a problem of ing coordinates. Now I have not figured out what is going on.Code

Void setisotropic (HDC, int cxclient, int cyclient) {// set the ing mode to mm_isoropicsetmapmode (HDC, mm_isotropic); // set the Windows window size to 1000*1000, the window cannot be seen. The window data is used to display the setjavaswextex (HDC, null) in the view. // the following two sentences are still not understood and cannot be properly explained, the following-When cyclient is changed to cyclient, the clock will reverse up and down setviewportextex (HDC, cxclient/2,-cyclient/2, null); // setviewportorgex (HDC, cxclient/2, cyclient/2, null );}

Setviewportextex (HDC, cxclient/2,-cyclient/2, null );

Why should we make negative cyclient in this place? Related to drawing? Why is it wrong? Depressed.