Нарисовать прямоугольник, который вращается вокруг своего центра (код не работает правильно)

//---------------------------------------------------------------------------
 
#include <vcl.h>
#include "math.h"
#pragma hdrstop
 
#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
int x=0,y=0,Angle=0;
int x1,x2,x3,x4,y1,y2,y3,y4;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::PaintBox1Paint(TObject *Sender)
{
 
Canvas->Brush->Color = clBlue;
x=(200+600+200+600)/4;
y=(200+200+400+400)/4;
Canvas->Rectangle(200,200,600,400);
}
//---------------------------------------------------------------------------
 
 
void TForm1::Rectangle(int Angle)
{
    x1 = (200-x)*cos(Angle) - (200-y)*sin(Angle)+x;
    y1 = (200-x)*sin(Angle) + (200-y)*cos(Angle)+y;
    x2 =  (600-x)*cos(Angle) - (200-y)*sin(Angle)+x;
    y2 =  (600-x)*sin(Angle) + (200-y)*cos(Angle)+y;
    x3 =  (200-x)*cos(Angle) - (400-y)*sin(Angle)+x;
    y3 = (200-x)*sin(Angle) + (400-y)*cos(Angle)+y;
    x4 = (600-x)*cos(Angle) - (400-y)*sin(Angle)+x;
    y4 = (600-x)*sin(Angle) + (400-y)*cos(Angle)+y;
    Canvas->Rectangle(x1,y1,x4,y4);
}
void __fastcall TForm1::Timer1Timer(TObject *Sender)
{
Angle+=5;
Canvas->Brush->Color=clBlue;
Rectangle(Angle);
 
}
//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
 
#include <vcl.h>
#pragma hdrstop
 
#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
  DoubleBuffered = 1;
  Timer1->Interval = 100;
}
//---------------------------------------------------------------------------
void rectangle(TCanvas *canvas, TColor pen_color, TColor brush_color, int x1, int y1, int x2, int y2, double angle)
{
  angle *= M_PI/180;
  canvas->Pen->Color = pen_color;
  canvas->Brush->Color = brush_color;
  int half_difx = abs(x2-x1)/2, half_dify = abs(y2-y1)/2, r = sqrt(half_difx * half_difx + half_dify * half_dify);
  int minx = x1 < x2 ? x1 : x2, miny = y1 < y2 ? y1 : y2;
  TPoint center = TPoint(minx+half_difx, miny+half_dify);
  double angle2 = atan(1.*half_dify / half_difx);
  canvas->MoveTo(center.x - r*cos(angle2 + angle), center.y + r*sin(angle2 + angle));
  canvas->LineTo(center.x + r*cos(angle2 - angle), center.y + r*sin(angle2 - angle));
  canvas->LineTo(center.x + r*cos(angle2 + angle), center.y - r*sin(angle2 + angle));
  canvas->LineTo(center.x - r*cos(angle2 - angle), center.y - r*sin(angle2 - angle));
  canvas->LineTo(center.x - r*cos(angle2 + angle), center.y + r*sin(angle2 + angle));
  canvas->FloodFill(center.x, center.y, canvas->Pixels[center.x][center.y], fsSurface);
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Timer1Timer(TObject *Sender)
{
  Refresh();
  static double angle = 0;
  rectangle(Canvas, clBlack, clBlue, 100, 300, 400, 100, angle++);
}
//---------------------------------------------------------------------------