TPNGImage - Alphachannel in Bitmap anzeigen

[Khabarakh]

Du musst beachten, dass AlphaScanline ein Byte, Scanline aber ein TRGBQuad (bzw. je nach PixelFormat) liefert.
Mit meinem Avatar erfolgreich getestet:

Delphi-Quellcode:

  TCardinalArray = Array[0..0] of Cardinal;
  PCardinalArray = ^TCardinalArray;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
  Png: TPNGObject;
  x, y: Integer;
  pTo: PCardinalArray;
  pFrom: PByteArray;
  Alpha: Byte;
begin
  if OpenPictureDialog1.Execute then
  begin
    Png := TPNGObject.Create;
    try
      Png.LoadFromFile(OpenPictureDialog1.FileName);

      Image1.Width := Png.Width * 2;
      Image1.Height := Png.Height;
      Image1.Picture.Bitmap.Width := Png.Width * 2;
      Image1.Picture.Bitmap.Height := Png.Height;
      Image1.Picture.Bitmap.PixelFormat := pf32bit;
      Image1.Canvas.Draw(0, 0, Png);
      
      for y := 0 to Png.Height - 1 do
      begin
        pFrom := Png.AlphaScanline[y];
        pTo := Image1.Picture.Bitmap.ScanLine[y];
        for x := 0 to Png.Width - 1 do
        begin
          Alpha := pFrom[x];
          pTo[x + Png.Width] := Alpha or Alpha shl 8 or Alpha shl 16;
        end;
      end;
    finally
      Png.Free;
    end;
  end;
end;