Komisches Problem beim Neuzeichnen

[Rastaman]

Hallo.
Ich hab einfach n bischn rumgespielt und bin auf ne komische Sache gestoßen.
Folgendes soll einen Kreis zeichnen, dessen Radius man in einem Edit editieren kann.
Das Problem zu schildern wäre zu kompliziert, probierts einfach mal aus

Delphi-Quellcode:

program TestProg;

uses
  Messages,
  Windows;

const
  CLASSNAME                 = 'WindowClass';
  STYLEFLAGS                = WS_SYSMENU;
  STYLEFLAGSEDIT            = ES_AUTOHSCROLL or WS_BORDER or WS_CHILD or WS_VISIBLE;
var
  WndClassInfo: TWndClass;
  Msg: TMsg;

  Mittelpunkt: TPoint = (
    X: 200;
    Y: 180);
  Radius: Integer = 5;

function CreateControls(Handle: HWND): Boolean;
var
  ControlArray: Array [0..1] of HWND;
begin
  Result := True;
  ControlArray[0] := CreateWindow('EDIT', '5', STYLEFLAGSEDIT,
    0, 0, 30, 20, Handle, 1, hInstance, nil);

  if not IsWindow(ControlArray[0]) then
    Result := False;
end;

function WndProc(hWnd: HWND; uMsg: UINT; wParam: WPARAM;
  lParam: LPARAM): LRESULT; stdcall;
var
  ps: TPaintStruct;
  WndDC: HDC;
  Brush, BrushOld: HBRUSH;

  Buffer: Array [0..2] of Char;
  Code: Integer;
begin
  case uMsg of
    WM_CLOSE:
      begin
        DestroyWindow(hWnd);
        PostQuitMessage(0);
        Result := 0;
      end;
    WM_COMMAND:
      begin
        if HiWord(wParam) = EN_CHANGE then
        begin
          SendMessage(GetDlgItem(hWnd, 1), WM_GETTEXT, 3, Integer(@Buffer));
          Val(Buffer, Radius, Code);
          SendMessage(hWnd, WM_PAINT, 0, 0);
          Result := 0;
        end;
      end;
    WM_CREATE:
      begin
        if not CreateControls(hWnd) then
          SendMessage(hWnd, WM_CLOSE, 0, 0);

        SendMessage(GetDlgItem(hWnd, 1), EM_LIMITTEXT, 2, 0);
        ShowWindow(hWnd, SW_SHOW);
        Result := 0;
      end;
    WM_PAINT:
      begin
        WndDC := BeginPaint(hWnd, ps);
        Brush := CreateSolidBrush($00C8D0D4);
        BrushOld := SelectObject(WndDC, Brush);
        RectAngle(WndDC, -1, -1, 401, 361);
        SelectObject(WndDC, BrushOld);
        DeleteObject(Brush);
        Ellipse(WndDC, Mittelpunkt.X - Radius, Mittelpunkt.Y - Radius,
          Mittelpunkt.X + Radius, Mittelpunkt.Y + Radius);
        EndPaint(WndDC, ps);
        Result := 0;
      end;
  else
    Result := DefWindowProc(hWnd, uMsg, wParam, lParam);
  end;
end;

begin
  with WndClassInfo do
  begin
    style := CS_VREDRAW or CS_HREDRAW;
    lpfnWndProc := @WndProc;
    hInstance := hInstance;
    hCursor := LoadCursor(0, IDC_ARROW);
    hbrBackground := COLOR_APPWORKSPACE;
    lpszClassName := CLASSNAME;
  end;

  RegisterClass(WndClassInfo);

  CreateWindow(CLASSNAME, 'Test Prog', STYLEFLAGS,
    440, 332, 400, 360, 0, 0, hInstance, nil);

  while GetMessage(Msg, 0, 0, 0) do
  begin
    TranslateMessage(Msg);
    DispatchMessage(Msg);
  end;

end.

Danke!