jQuery UI Signature

You can render an image from the signature JSON text on the server. The following shows how to do this in Java. You would call this code as follows:

SigGen.generateSignature(jsonEncoding, signatureOut);

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.imageio.ImageIO;

public class SigGen {

    private static final String IMAGE_FORMAT = "png";
    private static final int SIGNATURE_HEIGHT = 200;
    private static final int SIGNATURE_WIDTH = 400;

    /**
     * A point along a line within a signature.
     */
    private static class Point {

        private int x;
        private int y;

        public Point(float x, float y) {
            this.x = Math.round(x);
            this.y = Math.round(y);
        }
    }

    /**
     * Extract a signature from its JSON encoding and redraw it as an image.
     *
     * @param  jsonEncoding  the JSON representation of the signature
     * @param  output        the destination stream for the image
     * @throws  IOException  if a problem writing the signature
     */
    public static void generateSignature(String jsonEncoding, OutputStream output)
            throws IOException {
        output.write(redrawSignature(extractSignature(jsonEncoding)));
        output.close();
    }

    /**
     * Extract the signature lines and points from the JSON encoding.
     *
     * @param  jsonEncoding  the JSON representation of the signature
     * @return  the retrieved lines and points
     */
    private static List<List<Point>> extractSignature(String jsonEncoding) {
        List<List<Point>> lines = new ArrayList<List<Point>>();
        Matcher lineMatcher =
                Pattern.compile("(\\[(?:,?\\[-?[\\d\\.]+,-?[\\d\\.]+\\])+\\])").
                matcher(jsonEncoding);
        while (lineMatcher.find()) {
            Matcher pointMatcher =
                    Pattern.compile("\\[(-?[\\d\\.]+),(-?[\\d\\.]+)\\]").
                    matcher(lineMatcher.group(1));
            List<Point> line = new ArrayList<Point>();
            lines.add(line);
            while (pointMatcher.find()) {
                line.add(new Point(Float.parseFloat(pointMatcher.group(1)),
                        Float.parseFloat(pointMatcher.group(2))));
            }
        }
        return lines;
    }

    /**
     * Redraw the signature from its lines definition.
     *
     * @param  lines  the individual lines in the signature
     * @return  the corresponding signature image
     * @throws  IOException  if a problem generating the signature
     */
    private static byte[] redrawSignature(List<List<Point>> lines) throws IOException {
        BufferedImage signature = new BufferedImage(
                SIGNATURE_WIDTH, SIGNATURE_HEIGHT, BufferedImage.TYPE_BYTE_GRAY);
        Graphics2D g = (Graphics2D)signature.getGraphics();
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, signature.getWidth(), signature.getHeight());
        g.setColor(Color.BLACK);
        g.setStroke(new BasicStroke(2, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
        g.setRenderingHint(
                RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        Point lastPoint = null;
        for (List<Point> line : lines) {
            for (Point point : line) {
                if (lastPoint != null) {
                    g.drawLine(lastPoint.x, lastPoint.y, point.x, point.y);
                }
                lastPoint = point;
            }
            lastPoint = null;
        }
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        ImageIO.write(signature, IMAGE_FORMAT, output);
        return output.toByteArray();
    }
}

You can render an image from the signature JSON text on the server. The following shows how to do this in .NET 4.5 C#, thanks to Daniel Knight. You would call this code as follows and it returns a base64 encoded byte array as a string:

GetBase64Png(jsonEncoding, width, height);

using System;
using System.Collections.Generic;
using System.Web.Script.Serialization;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Web.Http;

public class GraphicsController : ApiController
{
	[HttpGet]
	[ActionName("GetBase64Png")]
	public string GetBase64Png([FromUri] string linesGraphicJSON, [FromUri] int width, [FromUri] int height)
	{
		return Draw2DLineGraphic(new JavaScriptSerializer().Deserialize<Signature>(linesGraphicJSON), width, height);
	}

	private string Draw2DLineGraphic(I2DLineGraphic lineGraphic, int width, int height)
	{
		//The png's bytes
		byte[] png = null;

		//Create the Bitmap set Width and height
		using (Bitmap b = new Bitmap(width, height))
		{
			using (Graphics g = Graphics.FromImage(b))
			{
				//Make sure the image is drawn Smoothly (this makes the pen lines look smoother)
				g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;

				//Set the background to white
				g.Clear(Color.White);

				//Create a pen to draw the signature with
				Pen pen = new Pen(Color.Black, 2);

				//Smooth out the pen, making it rounded
				pen.DashCap = System.Drawing.Drawing2D.DashCap.Round;

				//Last point a line finished at
				Point LastPoint = new Point();
				bool hasLastPoint = false;

				//Draw the signature on the bitmap
				foreach (List<List<double>> line in lineGraphic.lines)
				{
					foreach (List<double> point in line)
					{
						var x = (int)Math.Round(point[0]);
						var y = (int)Math.Round(point[1]);

						if (hasLastPoint)
						{
							g.DrawLine(pen, LastPoint, new Point(x, y));
						}

						LastPoint.X = x;
						LastPoint.Y = y;
						hasLastPoint = true;
					}
					hasLastPoint = false;
				}
			}

			//Convert the image to a png in memory
			using (MemoryStream stream = new MemoryStream())
			{
				b.Save(stream, ImageFormat.Png);
				png = stream.ToArray();
			}
		}
		return Convert.ToBase64String(png);
	}

	public class Signature : I2DLineGraphic
	{
		public List<List<List<double>>> lines { get; set; }
	}

	interface I2DLineGraphic
	{
		List<List<List<double>>> lines { get; set; }
	}
}

A full list of all possible settings is shown below. Note that not all would apply in all cases. For more detail see the documentation reference page.

$(selector).signature({
	background: '#ffffff', // Colour of the background
	color: '#000000', // Colour of the signature
	thickness: 2, // Thickness of the lines
	guideline: false, // Add a guide line or not?
	guidelineColor: '#a0a0a0', // Guide line colour
	guidelineOffset: 25, // Guide line offset from the bottom
	guidelineIndent: 10, // Guide line indent from the edges
	// Error message when no canvas
	notAvailable: 'Your browser doesn\'t support signing',
	scale: 1, // A scaling factor for rendering the signature (only applies to redraws).
	syncField: null, // Selector for synchronised text field
	syncFormat: 'JSON', // The output respresentation: 'JSON' (default), 'SVG', 'PNG', 'JPEG'
	svgStyles: false, // True to use style attribute in SVG
	change: null // Callback when signature changed
});

$.kbw.signature.options // Access settings for all instances

$(selector).signature('option', settings) // Change the instance settings
$(selector).signature('option', name, value) // Change an instance setting

$(selector).signature('option') // Retrieve the instance settings
$(selector).signature('option', name) // Retrieve an instance setting

$(selector).signature('enable') // Enable the signature functionality
$(selector).signature('disable') // Disable the signature functionality

$(selector).signature('destroy') // Remove the signature functionality

$(selector).signature('clear') // Erase any signature
$(selector).signature('isEmpty') // Determine if there is no signature
$(selector).signature('toDataURL') // Convert the signature to an image in a data: URL
$(selector).signature('toJSON') // Convert the signature to JSON
$(selector).signature('toSVG') // Convert the signature to SVG
$(selector).signature('draw', sig) // Re-draw the signature from JSON, SVG, or a data: URL