class function MillimeterPerPixel(MM: Integer): Integer;
var
  PrinterDPI: Integer;
begin
  PrinterDPI := GetDeviceCaps(Printer.Handle, LOGPIXELSY);
  Result := Round((PrinterDPI / 25.4) * MM);
end;

procedure Print;
var
  Bmp: TBitmap;
  X: Integer;
  Y: Integer;
  Rect: TRect;
  BmpWidth: Integer;
  BmpHeight: Integer;
  PageWidth: Integer;
  PageHeight: Integer;
  PrintableAreaX: Integer;
  PrintableAreaY: Integer;
  Scale: Double;
  DiffHeight: Integer;
  DiffWidth: Integer;
begin
  if (PrintDialog.Execute) then
  begin
    try
      Printer.BeginDoc;
      Printer.Title := 'Treemap';

      Bmp := TBitmap.Create;
      Bmp.LoadFromFile('Bitmap.bmp');

      // 1 pixel = 0,1 mm
      SetMapMode(Printer.Canvas.Handle, MM_LOMETRIC);

      // get bmp measurements
      BmpWidth := Round(MillimeterPerPixel(Bmp.Width) / 10);
      BmpHeight := Round(MillimeterPerPixel(Bmp.Height) / 10);

      // get page margin
      X := Round((GetDeviceCaps(Printer.Handle, PHYSICALOFFSETX) * MillimeterPerPixel(1)) / 10);
      Y := Round((GetDeviceCaps(Printer.Handle, PHYSICALOFFSETY) * MillimeterPerPixel(1)) / 10);

      // page size
      PageWidth := Round((GetDeviceCaps(Printer.Handle, PHYSICALWIDTH) * MillimeterPerPixel(1))/10);
      PageHeight := Round((GetDeviceCaps(Printer.Handle, PHYSICALHEIGHT) * MillimeterperPixel(1))/10);

      // get printable area
      PrintableAreaX := PageWidth - (2*X);
      PrintableAreaY := PageHeight - (2*Y);

      // new starting point
      SetWindowOrgEx(Printer.Handle, X, -Y, nil);

      // define bounding rectangle
      Rect.TopLeft := Point(X, -Y);

      // if bmp height or width is greater than the printable area, it has to be scaled into page size
      if ((PrintableAreaX >= BmpWidth + X) and (PrintableAreaY >= BmpHeight + Y)) then
        Rect.BottomRight := Point(BmpWidth+X, -(BmpHeight+Y))
      else if ((PrintableAreaX >= BmpWidth + X) and (PrintableAreaY < BmpHeight + Y)) then
      begin
        Rect.BottomRight.Y := PrintableAreaY;
        Scale := BmpHeight / PrintableAreaY;
        Rect.BottomRight.X := Round(BmpWidth / Scale);
      end
      else if ((PrintableAreaX < BmpWidth + X) and (PrintableAreaY >= BmpHeight + Y)) then
      begin
        Rect.BottomRight.X := PrintableAreaX;
        Scale := BmpWidth / PrintableAreaX;
        Rect.BottomRight.Y := Round(BmpHeight / Scale);
      end
      else if ((PrintableAreaX < BmpWidth + X) and (PrintableAreaY < BmpHeight + Y)) then
      begin
        DiffWidth := BmpWidth - PrintableAreaX;
        DiffHeight := BmpHeight - PrintableAreaY;
        if(DiffHeight > DiffWidth) then
        begin
          Rect.BottomRight.Y := PrintableAreaY;
          Scale := BmpHeight / PrintableAreaY;
          Rect.BottomRight.X := Round(BmpWidth / Scale);
        end
        else
        begin
          Rect.BottomRight.X := PrintableAreaX;
          Scale := BmpWidth / PrintableAreaX;
          Rect.BottomRight.Y := Round(BmpHeight / Scale);
        end;
      end;

      // print
      Printer.Canvas.StretchDraw(Rect, Bmp);
    finally
      Printer.EndDoc;
      Bmp.Free;
    end;//try..finally
  end//if(PrintDialog...)
  else
    exit;
end;