Сообщения Windows и их обработка

program TestMessages;
uses
  Windows,
  Messages,
  Dialogs,
  Graphics,
  SysUtils;
const
  AppName = 'Test';
  maxx_size = 800;
maxy_size = 600;
 
Var
a, b, c, d, e, x, y:  Integer;
str: String;
w: char;
l, r: boolean;
 
  Window: HWnd;  
  Message: TMsg;
  WindowClass: TWndClass; 
function WindowProc (Window : HWnd; Message, WParam : LongInt; LParam : LongInt) : LongInt; stdcall;
Var
    dc : HDC;  
    MyPaint : TPaintStruct; 
    Brush : hBrush; 
    Pen : hPen;     
 
begin
  WindowProc := 0;
  case Message of
    wm_Destroy :
      begin 
        PostQuitMessage (0); 
      Exit;  
    end;
    wm_Paint:
    begin
      dc := BeginPaint (Window, MyPaint);
      Brush := CreateSolidBrush (RGB (a, b, c));
      Pen := CreatePen (PS_SOLID, 1, RGB (a, b, c)); 
      SelectObject (dc, Brush);
      SelectObject (dc, Pen);
      Rectangle(dc,0,0,maxx_size,maxy_size);
      TextOut(dc,10, 10, PAnsiChar(str), length(str)); 
      TextOut(dc, 20, 30, @w, 1); {9 çàäàíèå}
       //TextOut(dc,10, 10, PWideChar(str), length(str)); 
    Brush := CreateSolidBrush (RGB (255, 0, 0)); {10}
    SelectObject (dc, Brush);
    if l = true then Ellipse (dc, x, y, x+70, y+50);  
      DeleteObject (Pen);
      DeleteObject (Brush);
     EndPaint (Window, MyPaint);
      ReleaseDC (Window, dc);
          end;
  WM_CLOSE:
  begin
   If MessageDlg('Закрыть?',  mtConfirmation,MbOkCancel,0) <> idOK then
    exit;
  end;
  WM_CREATE:
  begin
   a:= 100;
   b:=600;
   c:=700;
  end;
  wm_Size :
   begin
   d:= hiword(lParam);
   e:= loword(lParam);
   str:= IntToStr(d) + IntToStr(e);
   end;
   wm_Char: 
   begin
     w:=chr(wParam);
     InvalidateRect(Window, nil, False);
 
   end;
   wm_LButtonDown:  
   begin
 
   x:= loword(lParam);
   y:= hiword(lParam);
   l:= true;
   InvalidateRect(Window, nil, False);
  
   end;
   wm_RButtonDown:
   begin
   l:= false;
   InvalidateRect(Window, nil, False);
   end;
  end; 
  WindowProc := DefWindowProc (Window, Message, WParam, LParam); 
end;
begin
 
  with WindowClass do begin
    Style := cs_HRedraw or cs_VRedraw; 
    lpfnWndProc := @WindowProc; 
    cbClsExtra := 0; 
    cbWndExtra := 0;     
hInstance := 0;  
    hIcon := LoadIcon (0, idi_Application); 
    hCursor := LoadCursor (0, idc_Arrow);   
    hbrBackground := GetStockObject (White_Brush); 
    lpszMenuName := '';    
    lpszClassName := AppName;  
  end;
  If RegisterClass (WindowClass) = 0 then
     Halt (255); }
  Window := CreateWindow         (AppName,       
      'Форма',   
      ws_OverlappedWindow,  
      cw_UseDefault,
      cw_UseDefault, 
      800,         
      600,         
      0,           
      0,           
      HInstance,   
      nil);                
  ShowWindow (Window, CmdShow);
  UpdateWindow (Window); 
 while GetMessage (Message, 0, 0, 0) do 
    begin
    TranslateMessage (Message);       DispatchMessage (Message);   
 end; 
 Halt (Message.wParam); 
end.

if l = true then Ellipse (dc, x, y, x+70, y+50);

if L then
begin
   Ellipse (dc, x, y, x+70, y+50);
   TextOut(dc, x+70, y, @w, 1);
end;