怎样获取在canvas 画线的事件

var
stx,sty,midx,midy,endx,endy: integer ;
p1,p2,p3,p4,p5,p6 : TPoint ;MapCanvas := TmpCanvas ;
MapCanvas.Pen.Color := clblack;
MapCanvas.MoveTo(stx,sty);
MapCanvas.LineTo(midx,midy);
MapCanvas.LineTo(endx,endy);
MapCanvas.Brush.Color := clBlack;
MapCanvas.Polygon([p1,p2,p3]);
MapCanvas.Polygon([p4,p5,p6]);画好线后怎样在线条中获取鼠标双击事件！
多谢！