Возникла проблема

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  OpenGL;


type
  TformGL = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormPaint(Sender: TObject);
    procedure FormDestroy(Sender: TObject);

  private
    hrc: HGLRC;  
  end;

var
  formGL: TformGL;

implementation

{$R *.DFM}




procedure TformGL.FormPaint(Sender: TObject);
const
 a = 1;
var
 x,y,r : GLfloat;
 f : GLint;
begin
 wglMakeCurrent(Canvas.Handle, hrc);

 glViewPort (0, 0, ClientWidth, ClientHeight);

 glClearColor (1, 1, 1, 1.0);
 glClear (GL_COLOR_BUFFER_BIT);

 glEnable (GL_POINT_SMOOTH);
 glColor3f (0, 0, 0);

 glBegin (GL_POINTS);
For f := -3000 to 3000 do begin
   x := f/1000;
   y := 8*a*a*a/(x*x+4*a*a);
   glVertex2f (x/3,y/3);
  end;
 glEnd;

 glBegin(GL_LINE_STRIP);
   glVertex2f(-1,0);
   glVertex2f(1,0);
 glEnd;

 glBegin(GL_LINE_STRIP);
   glVertex2f(0,-1);
   glVertex2f(0,1);
 glEnd;

 SwapBuffers(Canvas.Handle);
 wglMakeCurrent(0, 0);
end;


procedure SetDCPixelFormat (hdc : HDC);
var
 pfd : TPixelFormatDescriptor;
 nPixelFormat : Integer;
begin
 FillChar (pfd, SizeOf (pfd), 0);
 pfd.dwFlags  := PFD_DRAW_TO_WINDOW or PFD_SUPPORT_OPENGL or PFD_DOUBLEBUFFER;
 nPixelFormat := ChoosePixelFormat (hdc, @pfd);
 SetPixelFormat (hdc, nPixelFormat, @pfd);
end;

procedure TformGL.FormCreate(Sender: TObject);
begin
 SetDCPixelFormat(Canvas.Handle);
 hrc := wglCreateContext(Canvas.Handle);
end;

procedure TformGL.FormDestroy(Sender: TObject);
begin
 wglDeleteContext(hrc);
end;

end.