Marching Ants on TImage inside TScrollbox (Erase Rect problem)

var
  Counter : Byte;
  CounterStart : Byte;
  Looper : LongInt;
  b:TBitmap;
  Region:TRect;
 
PROCEDURE RestrictCursorToDrawingArea (CONST Image: TImage);
  VAR
    CursorClipArea: TRect;
BEGIN
  CursorClipArea := Bounds(Image.ClientOrigin.X, Image.ClientOrigin.Y,
                                          Image.Width, Image.Height);
  Windows.ClipCursor(@CursorClipArea)
END {RestrictCursorToDrawingArea};
 
 
PROCEDURE RemoveCursorRestrictions;
BEGIN
  Windows.ClipCursor(NIL)
END {RemoveCursorRestrictions};
 
 
procedure MovingDots(X,Y: Integer; TheCanvas: TCanvas); stdcall;
begin
  Inc(Looper);
{$R-}
  Counter := Counter shl 1;              // Shift the bit left one
{$R+}
  if   Counter = 0
  then Counter := 1;          // If it shifts off left, reset it
  if   (Counter and 224) > 0  // Are any of the left 3 bits set?
  then
  begin
  TheCanvas.Pixels[X,Y] := clWhite   // Erase the pixel
  end else
  begin
    TheCanvas.Pixels[X,Y] := clBlack;  // Draw the pixel
  end;
 
end;
 
 
function NormalizeRect(R: TRect): TRect;
begin
  // This routine normalizes a rectangle. It makes sure that the Left,Top
  // coords are always above and to the left of the Bottom,Right coords.
  with R do
  BEGIN
    if   Left > Right
    then
      if   Top > Bottom
      then Result := Rect(Right,Bottom,Left,Top)
      else Result := Rect(Right,Top,Left,Bottom)
    else
      if   Top > Bottom
      then Result := Rect(Left,Bottom,Right,Top)
      else Result := Rect(Left,Top,Right,Bottom);
  END;
 
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
b:=Tbitmap.Create;
  X1 := 0;
  Y1 := 0;
  X2 := 0;
  Y2 := 0;
  Canvas.Pen.Color := Color;
  Canvas.Brush.Color := Color;
  CounterStart := 128;
  Timer1.Interval := 1;
  Timer1.Enabled := True;
  Looper := 0;
  scrollbox1.ControlStyle:=scrollbox1.ControlStyle+ [csOpaque];
end;
 
procedure TForm1.RemoveTheRect;
var
  R : TRect;
begin
  R := NormalizeRect(Rect(X1,Y1,X2,Y2));  // Rectangle might be flipped
  InflateRect(R,1,1);                     // Make the rectangle 1 pixel larger
  InvalidateRect(Handle,@R,True);         // Mark the area as invalid
  InflateRect(R,-2,-2);                   // Now shrink the rectangle 2 pixels
  ValidateRect(Handle,@R);                // And validate this new rectangle.
  // This leaves a 2 pixel band all the way around
  // the rectangle that will be erased & redrawn
  UpdateWindow(Handle);
end;
 
function TForm1.DrawTheRect:TRect;
begin
  // Determines starting pixel color of Rect
  Counter := CounterStart;
  // Use LineDDA to draw each of the 4 edges of the rectangle
  LineDDA(X1,Y1,X2,Y1,@MovingDots,LongInt(Image3.Canvas));
  LineDDA(X2,Y1,X2,Y2,@MovingDots,LongInt(Image3.Canvas));
  LineDDA(X2,Y2,X1,Y2,@MovingDots,LongInt(Image3.Canvas));
  LineDDA(X1,Y2,X1,Y1,@MovingDots,LongInt(Image3.Canvas));
  Result.Bottom:=y2;
  Result.Top:=y1;
  Result.Left:=x1;
  Result.Right:=x2;
end;
 
procedure TForm1.Timer1Timer(Sender: TObject);
begin
  CounterStart := CounterStart shr 2;    // Shl 1 will move rect slower
  if   CounterStart = 0                  // If bit is lost, reset it
  then CounterStart := 128;
  DrawTheRect                           // Draw the rectangle
end;
 
procedure TForm1.ImageMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
 X := X + Image3.Left;
 Y := Y + Image3.Top;
  RemoveTheRect;                               // Erase any existing rectangle
  X1 := X;
  Y1 := Y;
  X2 := X;
  Y2 := Y;
 // Force mouse movement to stay within TImage
  RestrictCursorToDrawingArea(Image3);
end;
 
procedure TForm1.ImageMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if ssLeft in Shift
  then  begin
 X := X + (Image3).Left;
 Y := Y + (Image3).Top;
    RemoveTheRect;         // Erase any existing rectangle
    X2 := X; Y2 := Y;      // Save the new corner where the mouse is
    Region:=DrawTheRect;           // Draw the Rect now... don't wait for the timer!
  end;
end;
 
procedure TForm1.ImageMouseUp(Sender: TObject;
  Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
RemoveCursorRestrictions;
end;