Capture Signature

HTML5 Canvas - Drawing and Saving Image

This is a javascript sample to capture a signature in a canvas area. And then you can save the image as required format. There are javascript functions handle the events in the canvas area. Then it capture the image data by todataurl().




Zetakey Sign & Send - Webapp

Capture Customer Signature onsite by browser

  • HTML5 Canvas Webapp
  • Capture Signature
  • Send to email
Launch App Source code

Live Demo of the source code

Download the source files - signature.js and signature.html

function signatureCapture() {
	var canvas = document.getElementById("newSignature");
	var context = canvas.getContext("2d");
	canvas.width = 276;
	canvas.height = 180;
	context.fillStyle = "#fff";
	context.strokeStyle = "#444";
	context.lineWidth = 1.5;
	context.lineCap = "round";
	context.fillRect(0, 0, canvas.width, canvas.height);
	var disableSave = true;
	var pixels = [];
	var cpixels = [];
	var xyLast = {};
	var xyAddLast = {};
	var calculate = false;
	{ 	//functions
		function remove_event_listeners() {
			canvas.removeEventListener('mousemove', on_mousemove, false);
			canvas.removeEventListener('mouseup', on_mouseup, false);
			canvas.removeEventListener('touchmove', on_mousemove, false);
			canvas.removeEventListener('touchend', on_mouseup, false);

			document.body.removeEventListener('mouseup', on_mouseup, false);
			document.body.removeEventListener('touchend', on_mouseup, false);
		}

		function get_coords(e) {
			var x, y;

			if (e.changedTouches && e.changedTouches[0]) {
				var offsety = canvas.offsetTop || 0;
				var offsetx = canvas.offsetLeft || 0;

				x = e.changedTouches[0].pageX - offsetx;
				y = e.changedTouches[0].pageY - offsety;
			} else if (e.layerX || 0 == e.layerX) {
				x = e.layerX;
				y = e.layerY;
			} else if (e.offsetX || 0 == e.offsetX) {
				x = e.offsetX;
				y = e.offsetY;
			}

			return {
				x : x, y : y
			};
		};

		function on_mousedown(e) {
			e.preventDefault();
			e.stopPropagation();

			canvas.addEventListener('mouseup', on_mouseup, false);
			canvas.addEventListener('mousemove', on_mousemove, false);
			canvas.addEventListener('touchend', on_mouseup, false);
			canvas.addEventListener('touchmove', on_mousemove, false);
			document.body.addEventListener('mouseup', on_mouseup, false);
			document.body.addEventListener('touchend', on_mouseup, false);

			empty = false;
			var xy = get_coords(e);
			context.beginPath();
			pixels.push('moveStart');
			context.moveTo(xy.x, xy.y);
			pixels.push(xy.x, xy.y);
			xyLast = xy;
		};

		function on_mousemove(e, finish) {
			e.preventDefault();
			e.stopPropagation();

			var xy = get_coords(e);
			var xyAdd = {
				x : (xyLast.x + xy.x) / 2,
				y : (xyLast.y + xy.y) / 2
			};

			if (calculate) {
				var xLast = (xyAddLast.x + xyLast.x + xyAdd.x) / 3;
				var yLast = (xyAddLast.y + xyLast.y + xyAdd.y) / 3;
				pixels.push(xLast, yLast);
			} else {
				calculate = true;
			}

			context.quadraticCurveTo(xyLast.x, xyLast.y, xyAdd.x, xyAdd.y);
			pixels.push(xyAdd.x, xyAdd.y);
			context.stroke();
			context.beginPath();
			context.moveTo(xyAdd.x, xyAdd.y);
			xyAddLast = xyAdd;
			xyLast = xy;

		};

		function on_mouseup(e) {
			remove_event_listeners();
			disableSave = false;
			context.stroke();
			pixels.push('e');
			calculate = false;
		};
	}
	canvas.addEventListener('touchstart', on_mousedown, false);
	canvas.addEventListener('mousedown', on_mousedown, false);
}

function signatureSave() {
	var canvas = document.getElementById("newSignature");// save canvas image as data url (png format by default)
	var dataURL = canvas.toDataURL("image/png");
	document.getElementById("saveSignature").src = dataURL;
};

function signatureClear() {
	var canvas = document.getElementById("newSignature");
	var context = canvas.getContext("2d");
	context.clearRect(0, 0, canvas.width, canvas.height);
}
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <script src="todataurl.js"></script>
        <script src="signature.js"></script>
    </head>
    <body>
        <div id="canvas">
            <canvas class="roundCorners" id="newSignature"
            style="position: relative; margin: 0; padding: 0; border: 1px solid #c4caac;"></canvas>
        </div>
        <script>signatureCapture();</script>
        <button type="button" onclick="signatureSave()">Save signature</button>
        <button type="button" onclick="signatureClear()">Clear signature</button>
        </br>
        Saved Image
        </br>
        <img id="saveSignature" alt="Saved image png"/>
    </body>
</html>