Metodo createChart (C#)

private void createChart(DataTable dt) {
  // Area di lavoro
  int w = 300;
  int h = 300;
  Bitmap bas = new Bitmap(w, h);
  Graphics area = Graphics.FromImage(bas);

  //Sfondo Bianco
  Rectangle rect = new Rectangle(0, 0, w, h);
  area.FillRectangle(Brushes.White, rect);

  //Lettura dati
  int x = 10;
  int y = 0;
  foreach (DataRow row in dt.Rows){
    
    int qta = ((int)row["qta"]) / 10;
    y = h - qta -10;
    
    Rectangle colonna = new Rectangle(x, y, 5, qta);
    
    if (x/2 == 0){
      area.FillRectangle(Brushes.Red, colonna);
      x += 7;
    } else {
      area.FillRectangle(Brushes.Blue, colonna);
      x += 15;
    }
  }

  area.DrawLine(Pens.Black, 0, y - 70, 0, h); // asse x
  area.DrawLine(Pens.Black, 0, h - 1, (x + 10), h - 1); // asse y
  bas.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Gif);
  bas.Dispose();
}