package org.davidmoten.hilbert;
   
   import java.awt.BasicStroke;
   import java.awt.Color;
   import java.awt.Graphics2D;
   import java.awt.image.BufferedImage;
   import java.io.File;
   import java.io.IOException;
   import java.math.BigInteger;
  
  import javax.imageio.ImageIO;
  
  import org.davidmoten.hilbert.exceptions.IORuntimeException;
  
  public final class HilbertCurveRenderer {
  
      private HilbertCurveRenderer() {
          // prevent instantiation
      }
  
      public static void renderToFile(int bits, int width, String filename) {
          BufferedImage b = render(bits, width);
          try {
              ImageIO.write(b, "PNG", new File(filename));
          } catch (IOException e) {
              throw new IORuntimeException(e);
          }
      }
  
      public static BufferedImage render(int bits, int width) {
          int dimensions = 2;
          HilbertCurve c = HilbertCurve.bits(bits).dimensions(dimensions);
          int n = 1 << bits;
          int height = width;
          BufferedImage b = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
          Graphics2D g = b.createGraphics();
          g.setBackground(Color.white);
          g.fillRect(0, 0, width, height);
          g.setPaint(Color.black);
          g.setStroke(new BasicStroke(0.5f));
          int margin = 10;
          int cellSize = (width - 2 * margin) / (n);
          int x = margin + cellSize / 2;
          int y = margin + cellSize / 2;
          for (long i = 0; i < n * n; i++) {
              long[] point = c.point(BigInteger.valueOf(i));
              int x2 = (int) Math.round((double) point[0] / (n - 1) * (width - 2 * margin - cellSize) + margin)
                      + cellSize / 2;
              int y2 = (int) Math.round((double) point[1] / (n - 1) * (height - 2 * margin - cellSize) + margin)
                      + cellSize / 2;
              g.drawLine(x, y, x2, y2);
              x = x2;
              y = y2;
          }
          return b;
      }
  }