PNG Image Gradient

[Blup]

Transparente abgerundete Ecken:

Delphi-Quellcode:

function CreateGrayScalePalette: HPalette;
var
  LogPalette: TMaxLogPalette;
  b: Byte;
begin
  LogPalette.palVersion    := $300;
  LogPalette.palNumEntries := 256;
  for b := 0 to 255 do
  begin
    with LogPalette.palPalEntry[b] do
    begin
      peRed   := b;
      peGreen := b;
      peBlue  := b;
    end;
  end;
  Result := CreatePalette(@LogPalette);
end;

procedure Set8BitGrayScale(ABitmap: TBitmap);
begin
  ABitmap.PixelFormat := pf8Bit;
  ABitmap.Palette := CreateGrayScalePalette;
end;

procedure SetAlphaRoundRect(AImage: TPngImage; dx, dy: Integer);
var
  BmpAlpha: TBitmap;
  y: Integer;
begin
  BmpAlpha := TBitmap.Create;
  try
    Set8BitGrayScale(BmpAlpha);
    {Hintergrund Schwarz}
    BmpAlpha.Canvas.Brush.Color := clBlack;
    BmpAlpha.SetSize(AImage.Width, AImage.Height);
    {sichtbaren Bereich Weiss füllen}
    BmpAlpha.Canvas.Pen.Style := psClear;
    BmpAlpha.Canvas.Brush.Color := clWhite;
    BmpAlpha.Canvas.RoundRect(BmpAlpha.Canvas.ClipRect, dx, dy);
    {Daten aus der Bitmap in den Alphachannel übernehmen}
    AImage.CreateAlpha;
    for y := 0 to AImage.Height - 1 do
    begin
      Move(BmpAlpha.ScanLine[y]^, AImage.AlphaScanline[y]^, AImage.Width);
    end;
  finally
    BmpAlpha.Free;
  end;
end;

procedure TForm1.TestClick(Sender: TObject);
var
  Image: TPngImage;
begin
  Image := TPngImage.Create;
  try
    Image.LoadFromFile('Background_Blue.png');

    SetAlphaRoundRect(Image, 20, 20);

    PaintBox1.Canvas.Draw(0, 0, Image);
  finally
    Image.Free;
  end;
end;