先看下效果：

主要代码在FormPaint上。
代码如下：

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormPaint(Sender: TObject);
    procedure FormResize(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  var
  x,t: Integer;
  y,a: Double;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  self.DoubleBuffered:=true;
  //设置双缓冲 防止图形闪烁
end;

procedure TForm1.FormPaint(Sender: TObject);
begin
  t:=1;      //绘制周期数
  Canvas.Pen.Width:=1;
  Canvas.MoveTo(0,Trunc(self.ClientHeight/2)); //找到高度的中心线准备画图
  for x := 0 to self.ClientWidth do
  begin
   a := (x/self.ClientWidth) * t * 2 * Pi;
   //y := Cos(a);    //余弦
   y:=Sin(a);      //正弦
   y := (1-y)*self.ClientHeight/2;     //振幅为二分之一的高度
   Canvas.LineTo(Trunc(x), Trunc(y));
  end;
end;

procedure TForm1.FormResize(Sender: TObject);
  begin
   Refresh;
end;

end.