// uses Math;
type
  TForm1 = class (TForm)
    Panel1: TPanel;
    Panel2: TPanel;
    procedure FormPaint (Sender: TObject);
    procedure PanelMouseDown (Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
    procedure PanelMouseMove (Sender: TObject; Shift: TShiftState; X,Y: Integer);
    procedure PanelMouseUp (Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
  private
    FAnchor : TPoint; // Mausposition zu Beginn des Verschiebens
    FOrgPos : TPoint; // Position des Controls vor dem Verschieben
    FPanning : Boolean; // True während des Verschiebens
  end;

CONST
  GRIDINTERVAL = 16;

type
  TPin = (pinBody, pinLeft, pinTop, pinRight, pinBottom);

// zeichnet einen Vektor mit einer Pfeilspitze
procedure DrawVector (aCanvas: TCanvas;
                      x1, y1, x2, y2: Integer;
                      aHeadSize: Integer = 5;
                      aFillHead: Boolean = False);
const
  ApexAngle = 30 * Pi / 180;
var
  dx, dy : Integer;
  angle : Double;
  s1, c1 : Extended;
  s2, c2 : Extended;
  P1, P2 : TPoint;
begin
  aCanvas.MoveTo (x1, y1);
  aCanvas.LineTo (x2, y2);

  if (x1 <> x2) then
    angle := {Math.}ArcTan2(y2 - y1, x2 - x1)
  else
    if (y1 < y2) then
      angle := Pi / 2
    else
      angle := 3 * Pi / 2;

  {Math.}SinCos (angle - ApexAngle, s1, c1);
  {Math.}SinCos (angle + ApexAngle, s2, c2);

  P1.x := x2 - Round(c1 * aHeadSize);
  P1.y := y2 - Round(s1 * aHeadSize);
  P2.x := x2 - Round(c2 * aHeadSize);
  P2.y := y2 - Round(s2 * aHeadSize);

  if aFillHead then
    aCanvas.Polygon ([P1, Point(x2, y2), P2])
  else
    begin
      aCanvas.MoveTo (P1.x, P1.y);
      aCanvas.LineTo (x2, y2);
      aCanvas.MoveTo (P2.x, P2.y);
      aCanvas.LineTo (x2, y2);
    end;
end;

// Liefert die Position eines Anschlußpunktes für ein Control
function PinPosition (aControl: TControl; aPin: TPin): TPoint;
var
  w2, h2 : Integer;
begin
  w2 := aControl.Left + aControl.Width div 2;
  h2 := aControl.Top + aControl.Height div 2;
  case aPin of
    pinLeft: Result := Point(aControl.Left, h2);
    pinTop: Result := Point(w2, aControl.Top);
    pinRight: Result := Point(aControl.Left + aControl.Width, h2);
    pinBottom: Result := Point(w2, aControl.Top + aControl.Height);
  else
    Result := Point(w2, h2);
  end;
end;

procedure TForm1.PanelMouseDown (Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  FAnchor := Mouse.CursorPos;
  FOrgPos := TControl(Sender).BoundsRect.TopLeft;
  FPanning := True;
end;

procedure TForm1.PanelMouseMove (Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
var
  xPos, yPos : Integer;
begin
  if FPanning then
    begin
      xPos := FOrgPos.X + (Mouse.CursorPos.X - FAnchor.X);
      yPos := FOrgPos.Y + (Mouse.CursorPos.Y - FAnchor.Y);
      TControl(Sender).Left := xPos - (xPos mod GRIDINTERVAL);
      TControl(Sender).Top := yPos - (yPos mod GRIDINTERVAL);
      Invalidate;
    end;
end;

procedure TForm1.PanelMouseUp (Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  FPanning := False;
end;

procedure TForm1.FormPaint (Sender: TObject);
var
  P1, P2 : TPoint;
begin
  inherited;
  // zeichne eine Verbindung von Panel1 (rechter Anschlußpunkt) zu Panel2 (linker Anschlußpunkt)
  P1 := PinPosition(Panel1, pinRight);
  P2 := PinPosition(Panel2, pinLeft);
  Canvas.Pen.Color := clBlue;
  Canvas.Brush.Color := clBlue;
{
  Canvas.Pen.Width := 2;
  Canvas.MoveTo (P1.X, P1.Y);
  Canvas.LineTo (P2.X, P2.Y);
}
  DrawVector (Canvas, P1.X, P1.Y, P2.X, P2.Y, 10, True);
end;

end.