procedure WMNCHITTEST(var Message : TMessage); message  WM_NCHITTEST;

...

procedure TMoveControl.WMNCHITTEST(var Message: TMessage);
begin
 if not (csDesigning in ComponentState) then begin
   Message.Result := HTCAPTION;
   if Assigned(FOnMove) then begin
     FOnMove(Self);
   end;
 end else
   Message.Result := HTCLIENT;
end;

unit MoveControl;

interface

uses
 SysUtils, Classes, Controls, Messages, WinProcs, Graphics;

type
 TMoveEvent = procedure(Sender: TObject; const X, Y: Integer) of object;
 TPaintEvent = procedure(Sender: TObject; Canvas: TCanvas) of object;

 TMoveControl = class(TCustomControl)
 private
   FOnMove: TMoveEvent;
   FOnPaint: TPaintEvent;
   { Private declarations }
 protected
   { Protected declarations }
   procedure Paint; override;
   procedure WMNCHITTEST(var Message : TMessage); message  WM_NCHITTEST;
   procedure WMMOVE(var Message : TMessage); message WM_MOVE;
 public
   { Public declarations }
   constructor Create(AOwner: TComponent); override;
 published
   { Published declarations }
   property OnMove: TMoveEvent read FOnMove write FOnMove;
   property OnPaint: TPaintEvent read FOnPaint write FOnPaint;
 end;

procedure Register;

implementation

procedure Register;
begin
 RegisterComponents('Samples', [TMoveControl]);
end;

{ TMoveControl }

constructor TMoveControl.Create(AOwner: TComponent);
begin
 inherited;
 Cursor := crSizeNWSE;
end;

procedure TMoveControl.Paint;
begin
 inherited;
 if not (csDesigning in ComponentState) and Assigned(OnPaint) then begin
   FOnPaint(Self, Canvas);
 end else begin
   Canvas.Brush.Style := bsSolid;
   Canvas.Brush.Color := clRed;
   Canvas.Pen.Color := clRed;
   Canvas.FillRect(ClientRect);
 end;
end;

procedure TMoveControl.WMMOVE(var Message: TMessage);
begin
 if Assigned(FOnMove) then begin
   FOnMove(Self, message.LParamLo, Message.LParamHi);
 end;
end;

procedure TMoveControl.WMNCHITTEST(var Message: TMessage);
begin
 if not (csDesigning in ComponentState) then begin
   Message.Result := HTCAPTION;
 end else
   Message.Result := HTCLIENT;
end;

end.