如何即时在程序中放大显示鼠标经过地方的图像?

procedure TForm16.Timer1Timer(Sender: TObject);
var
p:TPoint;
abc:blendFunction ;
x1,x2,y1,y2:integer;
begin
form1.doublebuffered:=true;
image1.picture.graphic:=Nil;
abc.AlphaFormat:=0;
abc.BlendFlags:=1;
abc.BlendOp:=AC_SRC_OVER;
abc.SourceConstantAlpha:=250;

GetCursorPos(p);
x1:=p.x-20;
x2:=p.x+20;
y1:=p.y-20;
y2:=p.y+20;
//AlphaBlend(image1.Canvas.Handle,0,0,image1.Width,image1.Height,getdc(0),x1,y1,x2,y2,abc);
Windows.AlphaBlend(image1.Canvas.Handle,0,0,image1.Width,image1.Height,getdc(0),x1,y1,50,50,abc);
end;