eu tenho istodelphi 2010 código:

unit Unit1;

interface

uses
    Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
    Dialogs, StdCtrls, Math, ExtCtrls, pngimage;

type
     TMyHintWindow = class(THintWindow)
     private
      FBitmap : TBitmap;
      ThePNG  : TPngImage;
      FRegion : THandle;
      procedure FreeRegion;
     protected
      procedure CreateParams(var Params : TCreateParams); override;
      procedure Paint; override;
      procedure Erase(var Message : TMessage); message WM_ERASEBKGND;
     public
      constructor Create(AOwner : TComponent); override;
      destructor Destroy; override;
      procedure  ActivateHint(Rect : TRect; const AHint : String); Override;
     end;

type
    TForm1 = class(TForm)
    Button1: TButton;
     procedure FormCreate(Sender : TObject);
    private
     { Private declarations }
    public
     { Public declarations }
    end;

var
   Form1 : TForm1;

implementation

{$R *.dfm}
// --------------------------------------------------------------------------- //
constructor TMyHintWindow.Create(AOwner : TComponent);
begin
     inherited Create(AOwner);
     FBitmap                  := TBitmap.Create;

     FBitmap.PixelFormat      := pf32bit;
     FBitmap.HandleType       := bmDIB;
     FBitmap.Transparent      := True;
     FBitmap.TransparentMode  := tmAuto;  // }tmFixed;
     FBitmap.TransparentColor := clWhite;
     FBitmap.AlphaFormat      := {afPremultiplied;  // }afDefined;

     ThePNG                   := TPngImage.Create;
     ThePNG.Transparent       := True;
     ThePNG.TransparentColor  := clWhite;
     ThePNG.LoadFromFile('D:\project-1\tooltip.png');

     FBitmap.LoadFromFile('D:\project-1\tooltip.bmp');
end;
// --------------------------------------------------------------------------- //
destructor TMyHintWindow.Destroy;
begin
     FBitmap.Free;
     FreeRegion;

     inherited;
end;
// --------------------------------------------------------------------------- //
procedure TMyHintWindow.CreateParams(var Params : TCreateParams);
const
     CS_DROPSHADOW = $20000;
begin
     inherited;
     Params.Style := Params.Style - WS_BORDER;
     Params.WindowClass.Style := Params.WindowClass.Style or CS_DROPSHADOW;
end;
// --------------------------------------------------------------------------- //
procedure TMyHintWindow.FreeRegion;
begin
     if FRegion <> 0 then
     begin
      SetWindowRgn(Handle, 0, True);
      DeleteObject(FRegion);
      FRegion := 0;
     end;
end;
// --------------------------------------------------------------------------- //
procedure TMyHintWindow.ActivateHint(Rect : TRect; const AHint : String);
var
   i : Integer;
begin
     Caption             := AHint;
     Canvas.Font         := Screen.HintFont;
     FBitmap.Canvas.Font := Screen.HintFont;
     DrawText(Canvas.Handle, PChar(Caption), Length(Caption), Rect, DT_CALCRECT or DT_NOPREFIX);

     Width               := 230;  // (Rect.Right - Rect.Left) + 16;
     Height              := 61;   // (Rect.Bottom - Rect.Top) + 10;

     FBitmap.Width       := Width;
     FBitmap.Height      := Height;
     Left := Rect.Left;
     Top := Rect.Top;
     FreeRegion;

     with Rect do
      FRegion := CreateRoundRectRgn(1, 1, Width, Height, 3, 3);

     if FRegion <> 0 then
    SetWindowRgn(Handle, FRegion, True);

     AnimateWindowProc(Handle, 300, AW_BLEND);

     SetWindowPos(Handle, HWND_TOPMOST, Left, Top, 0, 0, SWP_SHOWWINDOW or SWP_NOACTIVATE or SWP_NOSIZE);
end;
// --------------------------------------------------------------------------- //
procedure TMyHintWindow.Paint;
var
   CaptionRect : TRect;
begin
     with FBitmap.Canvas do
     begin
      Font.Color  := clWindowText;
      Brush.Style := bsClear;
     end;    // with
     CaptionRect := Rect(25, 26, Width - 10, Height - 10);

     SetBkMode(Canvas.Handle, TRANSPARENT);
     DrawText(FBitmap.Canvas.Handle, PChar(Caption), Length(Caption), CaptionRect, DT_WORDBREAK OR DT_NOPREFIX);
     BitBlt(Canvas.Handle, 0, 0, Width, Height, FBitmap.Canvas.Handle, 0, 0, SRCERASE{SRCCOPY});
end;
// --------------------------------------------------------------------------- //
procedure TMyHintWindow.Erase(var Message : TMessage);
begin
     Message.Result := 0;
end;
// --------------------------------------------------------------------------- //
procedure TForm1.FormCreate(Sender : TObject);
begin
     HintWindowClass := TMyHintWindow;
     Button1.Hint    := 'This is a nice fake tooltip!';
end;
// --------------------------------------------------------------------------- //
end.

Este exemplo temdois problemas:

Eu preciso desenhar o PNG com as bordas transparentes.A imagem em si é aqui

Se você executar este projeto (o formulário tem apenas um botão chamado Button1) e mostrar a dica algumas vezes, você deve perceber que a legenda se torna mais ousada toda vez que a dica é mostrada. Tenho certeza que eu esqueci um fundo que eu esqueci de apagar / apagar, mas não sei como consertar isso.

Alguém pode me dizer como corrigir esses dois problemas?