unit MainFormUnit;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs,
  ExtCtrls, Math;

type

  { TMainForm }

  TMainForm = class(TForm)
    Shape: TShape;
    procedure ShapeMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);

  private
    { private declarations }
  public
    { public declarations }
  end;

var
  MainForm: TMainForm;

implementation

{$R *.lfm}

const
  SYNC = 16;
  MOUSE_SEQUENCE : array[0..SYNC] of Word = (
    $0492, $0960, $0618, $014A,
    $0A41, $0249, $0096, $0861,
    $041A, $0168, $0690, $0942,
    $0A14, $0294, $0069, $0816,
    $04A1);

function SequenceToNybble(const s : Word) : Byte;
begin
  for Result := 0 to SYNC do if s = MOUSE_SEQUENCE[Result] then Exit;
  Result := 255;
end;

{ TMainForm }

procedure TMainForm.ShapeMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);

const
  lastX    : Integer = 0;
  lastY    : Integer = 0;
  Sequence : QWord = 0; // 64-Bit

var
  dx, dy : Byte;
  Nybble : Byte;
  b      : Byte;

begin

  dx := min(X - lastX + 1, 3);
  dy := min(Y - lastY + 1, 3);

  Sequence := (Sequence SHL 4) + (dx SHL 2) + dy;
  if (Sequence SHR 24) AND ($FFF) = MOUSE_SEQUENCE[SYNC] then
   begin

     Nybble := SequenceToNybble((Sequence SHR 12) AND ($FFF));
     if Nybble < SYNC then
      begin

        b := Nybble SHL 4;
        Nybble := SequenceToNybble(Sequence AND ($FFF));
        if Nybble < SYNC then
          begin

            Inc(b, Nybble);
            Shape.Brush.Color := RGBToColor(b, b, b);
            Sequence := 0;

          end;

      end;

   end;

  lastX := X;
  lastY := Y;

end;

end.