Procedure GetOGL_BMP(var BMP: TBitmap);
var
  Dimensions: array [0 .. 3] of Integer;
  RGBBits: PRGBQuad;
  Pixel: PRGBQuad;
  Header: PBitmapInfo;
  x, y: Integer;
  Temp: Byte;
begin
  glGetIntegerv(GL_VIEWPORT, @Dimensions);
  GetMem(RGBBits, Dimensions[2] * Dimensions[3] * 4);
  glFinish;
  glPixelStorei(GL_PACK_ALIGNMENT, 4);
  glPixelStorei(GL_PACK_ROW_LENGTH, 0);
  glPixelStorei(GL_PACK_SKIP_ROWS, 0);
  glPixelStorei(GL_PACK_SKIP_PIXELS, 0);
  glReadPixels(0, 0, Dimensions[2], Dimensions[3], GL_RGBA, GL_UNSIGNED_BYTE,
    RGBBits);
  if not Assigned(BMP) then
      BMP := TBitmap.Create;
  BMP.PixelFormat := pf32Bit;
  BMP.Width := Dimensions[2];
  BMP.Height := Dimensions[3];
  GetMem(Header, SizeOf(TBitmapInfoHeader));
  with Header^.bmiHeader do
  begin
    biSize := SizeOf(TBitmapInfoHeader);
    biWidth := Dimensions[2];
    biHeight := Dimensions[3];
    biPlanes := 1;
    biBitCount := 32;
    biCompression := BI_RGB;
    biSizeImage := Dimensions[2] * Dimensions[3] * 4;
  end;
  // Rot und Blau vertauschen
  Pixel := RGBBits;
  for x := 0 to Dimensions[2] - 1 do
    for y := 0 to Dimensions[3] - 1 do
    begin
      Temp := Pixel.rgbRed;
      Pixel.rgbRed := Pixel.rgbBlue;
      Pixel.rgbBlue := Temp;
      inc(Pixel);
    end;
  SetDIBits(BMP.Canvas.Handle, BMP.Handle, 0, Dimensions[3], RGBBits,
    TBitmapInfo(Header^), DIB_RGB_COLORS);

  FreeMem(Header);
  FreeMem(RGBBits);
end;