控件在运行状态改变大小

type
tddhsizebutton=class(tbutton)
public
PRocedure WmNcHitTest(var msg:TWmNcHitTest);
message wm_NcHitTest;
end;  

procedure TDdhSizeButton.WmNcHitTest(var msg:TWmNcHitTest);
var
pt:tpoint;
begin
  pt:=point(msg.xpos,msg.ypos);
  pt:=ScreentoClient(pt);
  if (pt.x<5) and (pt.y<5) then
  msg.Result:=httopright
  else if (pt.x>width-5) and (pt.y<5) then
  msg.Result:=httopright
  else if (pt.x >width-5) and (pt.y>height-5) then
  msg.Result:=htbottomright
  else if (pt.x<5) and (pt.y>height-5) then
  msg.Result:=htbottomleft
  else if (pt.x<5) then
  msg.Result:=htleft
  else if (pt.y<5) then
  msg.Result:=httop
  else if (pt.x>width-5) then
  msg.Result:=htright
  else if (pt.y>height-5) then
  msg.Result:=htbottom
  else
  inherited;
end;