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2008: Decision Year for RIAs - October 20-22, 2008 San Jose

Creating a Flex 2 Signature Grabber
My MAXUP Experience

By the time you read this, another MAX will be in the history books. In fact, with a record attendance of around 3,500 developers and designers, this MAX in Vegas will also be in the record books.

Along with the usual great conference sessions, this year there was a special event referred to as the "BarCamp - The unconference event" called MAXUP. I presented a MAXUP demo, A Flex 2 Signature Panel at MAXUP, where I showed the audience how easy it was to combine a Flex 2 UI for capturing a mouse-created signature with the ActionSript 3 Drawing API and a remote object call to a ColdFusion component. Leveraging work that James Ward blogged about on, I retooled the back-end as a ColdFusion CFC (I make remote object calls to the CFC's functions), and made some minor UI changes to create a signature panel that could be used for online NDA agreements or e-signatures.

Adobe Flex 2 Builder allowed me to lay out very quickly a simple UI where a user can use a mouse (or even better a drawing pen) to write out messages (See Figure 1).

The signature pad captures a visitor's IP address via a remote object call to a CFC method getVisitorIP() during the Flex application's initialize event:

<mx:Application xmlns:mx="" initialize=" roSign.getVisitorIP()"
creationComplete="setColor()" styleName="plain" viewSourceURL="srcview/index.html" horizontalAlign="center"

<mx:RemoteObject id="roSign"
fault=", 'Alert');"
<mx:method name="getVisitorIP" result="my_IP_handler(event.result)"/>
<mx:method name="doUpload" result="my_CFC_handler(event.result)"/>

<cffunction name="getVisitorIP" displayname=
"Get IP Address" hint="Returns Visitor's' IP address" access="remote" returntype="string">
<cfset sIP = "#CGI.Remote_Addr#">
<cfreturn sIP />

Clicking the 'Accept' button triggers the click event that calls the remote object doUpload and corresponding CFC method:

<mx:RemoteObject id="roSign"
fault=", 'Alert');"
<mx:method name="getVisitorIP" result="my_IP_handler(event.result)"/>
<mx:method name="doUpload" result="my_CFC_handler(event.result)"/>


private var sIP:String;
private function doSave():void {
var bd:BitmapData = new BitmapData(canvas.width,canvas.height);
var ba:ByteArray = PNGEnc.encode(bd); // See the code
roSign.doUpload(ba,sIP); // pass the ByteArray and the Visitor's IP address
<cffunction name="doUpload" displayname=
"Save Signature" hint="Saves a PNG Signature" access="remote" output="false" returntype="any">
<cfargument name="sigbytes" required="true" type="binary">
<cfargument name="ip_suffix" required="true" type="string">
var myUUID = "";
    var SigFileName = "";
<!--- create a FileOutputStream --->
<cfobject type="java" action="CREATE" class="" name="oStream">
    myUUID = CreateUUID(); // create a unique id

// call init method, passing in the full path to the desired jpg

SigFileName = getSigFileName("#arguments.ip_suffix#_#myUUID#");
<cfreturn SigFileName />

Once the doUpload method is complete, the event.result is returned (the dynamic file name [including both an IP address and a UUID] of the stored PNG image file) and assigned to a Flex string variable, SigFileName:

........ abbreviated for space saving ........
    private var SigFileName:String;

private function my_CFC_handler(result:Object):void {
SigFileName = result.toString();
btnView.enabled = true;

Clicking on the 'View' button triggers the click event and the function doView(), which opens the page and the saved PNG image as shown in Figure 2:

........ abbreviated for space saving ........

private function doView():void {
var u:URLRequest = new URLRequest("../welcome.cfm?sig=" + SigFileName + ".png");

The complete code listing is available at:
package {

    import flash.geom.*;
    import flash.display.*;
    import flash.utils.*;

    public class PNGEnc {

    public static function encode(img:BitmapData):ByteArray {
      // Create output byte array
      var png:ByteArray = new ByteArray();
      // Write PNG signature
      // Build IHDR chunk
      var IHDR:ByteArray = new ByteArray();
      IHDR.writeUnsignedInt(0x08060000); // 32bit RGBA
      // Build IDAT chunk
      var IDAT:ByteArray= new ByteArray();
      for(var i:int=0;i < img.height;i++) {
        // no filter
        var p:uint;
        if ( !img.transparent ) {
          for(var j:int=0;j < img.width;j++) {
          p = img.getPixel(j,i);
            uint(((p&0xFFFFFF) << 8)|0xFF));
        } else {
        for(var k:int=0;k < img.width;k++) {
        p = img.getPixel32(k,i);
          uint(((p&0xFFFFFF) << 8)|
    // Build IEND chunk
    // return PNG
    return png;

    private static var crcTable:Array;
    private static var crcTableComputed:Boolean = false;

    private static function writeChunk(png:ByteArray,
      type:uint, data:ByteArray):void {
    if (!crcTableComputed) {
      crcTableComputed = true;
      crcTable = [];
      for (var n:uint = 0; n < 256; n++) {
        var c:uint = n;
        for (var k:uint = 0; k < 8; k++) {
        if (c & 1) {
          c = uint(uint(0xedb88320) ^
            uint(c >>> 1));
         } else {
            c = uint(c >>> 1);
         crcTable[n] = c;
    var len:uint = 0;
    if (data != null) {
      len = data.length;
    var p:uint = png.position;
    if ( data != null ) {
    var e:uint = png.position;
    png.position = p;
    var d:uint = 0xffffffff;
    for (var i:int = 0; i < (e-p); i++) {
      d = uint(crcTable[
        (d ^ png.readUnsignedByte()) &
        uint(0xff)] ^ uint(d >>> 8));
    d = uint(d^uint(0xffffffff));
    png.position = e;

MAXUP was a great success. Although somewhat nervous before my presentation, I was grinning ear-to-ear afterwards from Adobe's Ted Patrick's encouragement. He said, "Mike, I like the way you used AMF to pass the byte-array to the server-side code." Thanks, Ted. (Figure 3)

Reflecting on how much easier it was to create this example compared to the two-month-long project of doing it with the Flash 7 IDE/Flex 1.5/CFMX 6.1/Apache Batik, I am simply amazed by Flex 2's versatility and efficiency in getting the job done quickly. If you still haven't had a chance to try out the Flex 2-CFMX 7.0.2 dynamic duo, I hope this example helps lure you in a bit further.

About Michael Givens
Mike Givens is the CTO of U Saw It Enterprises, a Web technology consulting firm based in Marietta, GA. He is an Adobe Corporate Champion known to share his experience and evangelism of all things Adobe. Certified in both ColdFusion 5 and as an Advanced CFMX Developer, he has been using ColdFusion since the days of Allaire Spectra. For the last 11 years, he has been seen with his head down - deep in the code.

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Reader Feedback: Page 1 of 1

Great Article! I've always thought it'd be a nice feature to capture someones signature digitally. I had no idea it would be that easy, relatively speaking. Thanks for the post.

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