完全透明的控件,可以获得事件

type
 TxControl=class(TWinControl)
  private
      procedure CreateParams(var Params: TCreateParams); override;
      procedure xControlMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
  public
   constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
 end;

{ TControl }

constructor TxControl.Create(AOwner: TComponent);
begin
  inherited;
ControlStyle :=ControlStyle - [csOpaque];
self.OnMouseDown:=self.xControlMouseDown;
end;

procedure TxControl.CreateParams(var Params: TCreateParams);
begin
  inherited CreateParams(Params);
  with Params do
  begin
  { 完全重画 }
    Style := Style and not WS_CLIPCHILDREN;
    Style := Style and not WS_CLIPSIBLINGS;
  { 增加透明 }
    ExStyle := ExStyle or WS_EX_TRANSPARENT;
  end;
end;

destructor TxControl.Destroy;
begin

  inherited;
end;

procedure TxControl.xControlMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
ReleaseCapture;
SendMessage(self.Parent.Handle,WM_SYSCOMMAND,SC_MOVE+HTCaption,0);
end;