как сделать график ?

unit unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, ExtCtrls, XPMan;
 
type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Label1: TLabel;
    Label2: TLabel;
    Edit2: TEdit;
    ColorBox1: TColorBox;
    ColorBox2: TColorBox;
    Label3: TLabel;
    Label4: TLabel;
    Button1: TButton;
    Button2: TButton;
    Label5: TLabel;
    Label6: TLabel;
    procedure Edit1KeyPress(Sender: TObject; var Key: Char);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure FormActivate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
 x1,x2,x,y,dx,mx,my:real;
 color1,color2:Tcolor;
  Form1: TForm1;
  a,b,g,x0,y0:integer;
 
implementation
 
{$R *.DFM}
 
 Function f(x:real):real;
 begin
 if (x<>0) and (b<>0 )then
  f:=sin(x+b)+cos(a);
 end;
 
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
case key of
 '0'..'9',#8:;
  else key:=Chr(0);
 end;
end;
 
procedure TForm1.Button1Click(Sender: TObject);
begin
if g<>1 then  MessageDlg('Очистите график',mtWarning,[mbOk],0)
else begin
If (Edit1.Text='') or (Edit2.Text='') then MessageDlg('Введите данные',mtWarning,[mbOk],0)
else
begin
Label5.Visible:=true;
Label6.Visible:=true;
g:=0;
a:=StrToInt(Edit1.Text);
b:=StrToInt(Edit2.Text);
x0:=250;y0:=283;x1:=0;
x2:=25;mx:=20;my:=20;
dx:=0.001;
color1:=ColorBox1.Selected;
color2:=ColorBox2.Selected;
with form1.Canvas do
begin
Pen.Color:=color1;
MoveTo(0,283);LineTo(500,283);
MoveTo(250,100);LineTo(250,500);
x:=x1;
repeat
y:=f(x);
Pixels[x0+Round(x*mx),y0-Round(y*my)]:=Color2;
x:=x+dx;
until (x>=x2);
end;
end;
end;
end;
 
procedure TForm1.Button2Click(Sender: TObject);
begin
g:=1;
with form1.Canvas do
begin
x:=x1;
repeat
y:=f(x);
Pixels[x0+Round(x*mx),y0-Round(y*my)]:=clWhite;
x:=x+dx;
until (x>=x2);
Pen.Color:=color1;
MoveTo(0,283);LineTo(500,283);
MoveTo(250,100);LineTo(250,500);
end;
end;
 
 
procedure TForm1.FormActivate(Sender: TObject);
begin
g:=1;
end;
 
end.