Ausfallswinkel berechnen und mit Canvas einzeichnen

[Uwe Raabe]

Delphi-Quellcode:

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
const
  cMax = 5;
var
  X0, X1: Integer;
  Y0, Y1: Integer;
  W, H: Integer;
  R: TRect;
  count: Integer;

  procedure MirrorY(Value: Integer); forward;

  procedure MirrorX(Value: Integer);
  begin
    if Count > cMax then Exit;
    X := Value;
    Y := Round(Y0 + (X - X0)*(Y1 - Y0)/(X1 - X0));
    if Y < R.Top then
      MirrorY(R.Top)
    else if Y > R.Bottom then
      MirrorY(R.Bottom)
    else begin
      Inc(Count);
      X1 := 2*X - X1;
      Canvas.LineTo(X, Y);
      X0 := X;
      Y0 := Y;
    end;
  end;

  procedure MirrorY(Value: Integer);
  begin
    if Count > cMax then Exit;

    Y := Value;
    X := Round(X0 + (Y - Y0)*(X1 - X0)/(Y1 - Y0));
    if X < R.Left then
      MirrorX(R.Left)
    else if X > R.Right then
      MirrorX(R.Right)
    else begin
      Inc(Count);
      Y1 := 2*Y - Y1;
      Canvas.LineTo(X, Y);
      X0 := X;
      Y0 := Y;
    end;
  end;

begin
  Self.Repaint;
  W := Shape1.Width div 2;
  H := Shape1.Height div 2;
  X0 := Shape1.Left + W;
  Y0 := Shape1.Top + H;

  with Shape2 do
    R := Rect(Left + W, Top + H, Left + Width - W, Top + Height - H);

  W := Shape2.Width;
  if shape2.Height > W then
    W := shape2.Height;

  Canvas.MoveTo(X0, Y0);
  X1 := X0 + 5*W*(X - X0);
  Y1 := Y0 + 5*W*(Y - Y0);
  Count := 0;
  while Count < cMax do begin
    if X1 < R.Left then
      MirrorX(R.Left)
    else if X1 > R.Right then
      MirrorX(R.Right)
    else if Y1 < R.Top then
      MirrorY(R.Top)
    else if Y1 > R.Bottom then
      MirrorY(R.Bottom)
    else
      Break;
  end;
  Canvas.LineTo(X1, Y1);
end;

procedure TForm1.Shape2MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  self.Repaint;
  Canvas.MoveTo(shape1.Left + (Shape1.Width div 2), Shape1.Top + (Shape1.Height div 2));
  Canvas.LineTo(shape2.Left + X, shape2.Top + Y);
end;