Визуально изобразить окружности (XE4, визуальный режим)

#include <vcl.h>
#pragma hdrstop
 
#include "Unit80.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm80 *Form80;
//---------------------------------------------------------------------------
__fastcall TForm80::TForm80(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------
double RingS(double R1, double R2)
{
    const PI = 3.141592653589793;
    return PI*(R1*R1 - R2*R2);
}
void __fastcall TForm80::Button1Click(TObject *Sender)
{
double Rmax = Edit1->Text.ToDouble(), Rmin = Edit2->Text.ToDouble();
    ShowMessage(String().sprintf(L"Площадь кольца = %8.3f", RingS(Rmax, Rmin)));
}

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  Canvas->FillRect(Canvas->ClipRect);  // или InvalidateRect(Handle, NULL, 1);
  double R1 = 300, R2 = 200;
  Canvas->Brush->Color = clGreen;
  Canvas->Ellipse(ClientWidth/2-R1/2, ClientHeight/2-R1/2, ClientWidth/2+R1/2, ClientHeight/2+R1/2);
  Canvas->Ellipse(ClientWidth/2-R2/2, ClientHeight/2-R2/2, ClientWidth/2+R2/2, ClientHeight/2+R2/2);
  Canvas->FloodFill(ClientWidth/2-R1/2+R2/2, ClientHeight/2, Color, fsSurface);
  Canvas->Brush->Color = Color;
  Canvas->FloodFill(ClientWidth/2, ClientHeight/2, clGreen, fsSurface);
}