Windows Programming [11]-wm_size message

In this example:

Program project1; uses Windows, messages; {custom process for wm_size message calling} procedure onsize (H: hwnd); var rect: trect; Pt: tpoint; Buf: array [0 .. 255] of char; begin getwindowrect (H, rect); {retrieve window rectangle} PT. x: = rect. right-rect. left; {extract width} PT. y: = rect. bottom-rect. top; {extract height} wvsprintf (BUF, 'width: % d, height: % d', @ pt); {format to buffer} setwindowtext (H, Buf ); {displayed in title} end; function wndproc (WND: hwnd; MSG: uint; wparam: integer; lparam: integer): integer; stdcall; begin result: = 0; case MSG of wm_size: onsize (WND); {messages that change the window size} wm_destroy: postquitmessage (0); else result: = defwindowproc (WND, MSG, wparam, lparam ); end; end; function regmywndclass: Boolean; var CLS: twndclass; begin Cls. style: = cs_hredraw or cs_vredraw; Cls. lpfnwndproc: = @ wndproc; Cls. cbclsextra: = 0; Cls. cbwndextra: = 0; Cls. hinstance: = hinstance; Cls. hicon: = 0; Cls. hcursor: = loadcursor (0, idc_arrow); Cls. hbrbackground: = hbrush (color_window + 1); Cls. lpszmenuname: = nil; Cls. lpszclassname: = 'mywnd'; Result: = registerclass (CLS) 0; end; {program entry} const tit = 'new form'; Ws = ws_overlappedwindow; X = 100; y = 100; W = 300; H = 180; var hwnd: thandle; MSG: tmsg; begin regmywndclass; hwnd: = createwindow ('mywnd', tit, WS, X, y, W, H, 0, 0, hinstance, nil); showwindow (hwnd, sw_shownormal); updatewindow (hwnd); While (getmessage (MSG, 0, 0, 0 )) do begin translatemessage (MSG); dispatchmessage (MSG); end.