tengo estodelphi 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 ejemplo tienedos cuestiones:

Necesito dibujar el PNG con los bordes transparentes.La imagen en sí está aquí.

Si ejecuta este proyecto (el formulario tiene solo un botón llamado Button1) y muestra la sugerencia varias veces, debe darse cuenta de que el título se vuelve más nítido cada vez que se muestra la sugerencia. Estoy bastante seguro de que olvidé un fondo. Olvidé borrar / borrar, pero no estoy seguro de cómo solucionarlo.

¿Puede alguien decirme cómo solucionar estos dos problemas?