(Delphi THintWindow) How to draw a transparent PNG

I have this delphi 2010 code:

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.

This example has two issues:

I need to draw the PNG with the transparent borders. The image itself is here
If you run this project (form has just a button called Button1), and show the hint few times, you should realize that caption becomes bolder every time the hint is shown. I'm pretty sure I forgot a background I forgot to clear/erase, but I'm not sure how to fix that.

Can someone please tell me how to fix these two issues?

You will to have to perform adaption for position and png in cas of hint needed above, but the "engine" should work as expected. I didn't use GDI+ which would i have made much easier.

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;
      FCurrAlpha:Integer;
      FTimer:TTimer;
      FActivated:Boolean;
      FLastActive:Cardinal;
      procedure PrepareBitmap;
      procedure IncAlpha(Sender:TObject);
     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;
     FCurrAlpha               := 1;
     FTimer                   := TTimer.Create(self);
     FTimer.Interval          := 20;
     Ftimer.OnTimer           := IncAlpha;
     Ftimer.Enabled           := false;
     ThePNG                   := TPngImage.Create;
     ThePNG.Transparent       := True;
     ThePNG.TransparentColor  := clWhite;
     ThePNG.LoadFromFile('C:\temp\0o36B.png');


end;
// --------------------------------------------------------------------------- //
destructor TMyHintWindow.Destroy;
begin
     FBitmap.Free;
     ThePNG.Free;
     inherited;
end;
// --------------------------------------------------------------------------- //

procedure TMyHintWindow.IncAlpha(Sender:TObject);
begin
    FCurrAlpha := FCurrAlpha + 10;
    if FCurrAlpha >= 254 then
        begin
           FCurrAlpha := 254;
           Ftimer.Enabled := false;
           FActivated := false;
        end;
    invalidate;
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;
// --------------------------------------------------------------------------- //



type
  pRGBQuadArray = ^TRGBQuadArray;
  TRGBQuadArray = ARRAY[0..$effffff] OF TRGBQuad;
Procedure SetAlpha(bmp:TBitMap;Alpha:Byte);
var
 pscanLine32 : pRGBQuadArray;
 i,j:Integer;
 begin
   Bmp.PixelFormat := pf32Bit;
   bmp.HandleType := bmDIB;
   bmp.ignorepalette := true;
   bmp.alphaformat := afDefined;
   for i := 0 to bmp.Height -1 do
     begin
     pscanLine32 := bmp.Scanline[i];
     for j := 0 to bmp.Width -1 do
        begin
          pscanLine32[j].rgbReserved := Alpha;
          pscanLine32[j].rgbBlue := 0;
          pscanLine32[j].rgbRed := 0;
          pscanLine32[j].rgbGreen := 0;
        end;
     end;
 end;

Procedure ResetSetAlpha(bmp:TBitMap;r:Trect;Alpha:Byte);
var
 pscanLine32 : pRGBQuadArray;
 i,j:Integer;
 begin
   for i := 0 to bmp.Height -1 do
     begin
     pscanLine32 := bmp.Scanline[i];
     for j := 0 to bmp.Width -1 do
        begin
          if (i>=r.Top) and (i<=r.Bottom) and (j>=r.Left) and (j<=r.Right) then
                pscanLine32[j].rgbReserved := Alpha;
        end;
     end;
 end;


procedure TMyHintWindow.PrepareBitmap;
var
 r:TRect;
begin
   r := Clientrect;
   r.Top := r.Top + 10;
   InflateRect(r,-10,-10);
   FreeAndNil(FBitmap);
   FBitmap := TBitmap.Create;
   FBitmap.Width := 230;
   FBitmap.Height := 61;
   SetAlpha(FBitmap, 0);
   FBitmap.Canvas.Font := Screen.HintFont;
   FBitmap.Canvas.Brush.Style := bsClear;
   FBitmap.Canvas.Draw(0, 0, ThePNG);
   DrawText(FBitmap.Canvas.Handle, PChar(Caption), Length(Caption), r,DT_Center or DT_Wordbreak or DT_NOPREFIX);
   ResetSetAlpha(FBitmap,r,255);
end;

// --------------------------------------------------------------------------- //
procedure TMyHintWindow.ActivateHint(Rect : TRect; const AHint : String);
var
   i : Integer;

begin
    if (GetTickCount - FLastActive > 250) and (Length(AHint) < 100) then

     if not FActivated then
        begin
         FCurrAlpha := 1;
         FActivated := true;
         Caption             := AHint;
         Canvas.Font         := Screen.HintFont;
         Width               := 230;  // (Rect.Right - Rect.Left) + 16;
         Height              := 61;   // (Rect.Bottom - Rect.Top) + 10;
         Left := rect.Left  - Width div 2;
         Top := Rect.Top;
         Ftimer.Enabled := true;
         ShowWindow(Handle, SW_SHOWNOACTIVATE);
         SetWindowPos(Handle, HWND_TOPMOST, Left, Top, 0, 0, SWP_NOACTIVATE or SWP_NOMOVE or SWP_NOSIZE);
         invalidate;
        end;
    FLastActive := GetTickCount;
end;

// --------------------------------------------------------------------------- //
procedure TMyHintWindow.Paint;
var
   DestPoint, srcPoint:TPoint;
   winSize:TSize;
   DC         : HDC;
   blendfunc  : BLENDFUNCTION;

    Owner : HWnd;
    curWinStyle:Integer;

     exStyle:Dword;
begin

   PrepareBitmap;
   DC := GetDC(0);

   try
   winSize.cx := width;
   winSize.cy := Height;
   srcPoint.x := 0;
   srcPoint.y := 0;

   DestPoint := BoundsRect.TopLeft;

   exStyle := GetWindowLongA(handle, GWL_EXSTYLE);
   if (exStyle and WS_EX_LAYERED) = 0 then

    SetWindowLong(handle, GWL_EXSTYLE, exStyle or WS_EX_LAYERED );



   With blendFunc do
   begin
     AlphaFormat := 1; //=AC_SRC_ALPHA;
     BlendFlags := 0;
     BlendOp := AC_SRC_OVER;
     SourceConstantAlpha :=  FCurrAlpha;  // here you can set Alpha
   end;
   UpdateLayeredWindow(Handle, DC, @DestPoint, @winSize, FBitmap.Canvas.Handle,  @srcPoint,clBlack, @blendFunc, 2);//=ULW_ALPHA

   finally
      ReleaseDC(0, DC);
   end;


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!';
     ReportMemoryLeaksOnShutDown := true;
end;
// --------------------------------------------------------------------------- //
end.