Abstract form

Canvas Intellisense in Visual Studio

Posted in Coding, Internet, JavaScript by Homam Hosseini on February 18, 2010

I was playing with HTML5 Canvas element to see how it could be useful in future web based game developments. I like that it is easier than GDI. I haven’t yet done much performance testing but it is definitely faster than making games by animating DOM elements.

Recently I had some free time so I decided to create vsdoc documention for Canvas element interface for Visual Studio. I added intellisense (auto competition) and some helps and tips.

Download canvas-vsdoc.js and canvas-utils.js from CodePlex.

It is tuned to work with VS2010, but we can make it work with VS2008 too.

canvas-vsdoc.js contains the intellisense documentation.

canvas-utils.js has a few utility functions (like detecting if the browser supports Canvas) and some enumeration types for things like Line Joins, Repeations, Text Aligns, etc.

To use the intellisense you need to reference canvas-vsdoc.js in the beginning of your JavaScript file, like this:

/// <reference path=”canvas-vsdoc.js” />

Note you can just drop the .js file and Visual Studio will write the reference.

Then use a utility method to get a reference to canvas element:

var canvas = Canvas.vsGet(document.getElementById("canvas1"));

Canvas.vsGet(element) receives a HTML element and returns the given element itself if it is in runtime. But in design time it returns Canvas.vsDoc.VSDocCanvasElement object that contains the documentations.

Then you can use the canvas element as usual:

var ctx = canvas.getContext("2d");
ctx.arc(50, 50, 25, 0, Math.PI, true);
…

Please note canvas-vsdoc.js must not be included  in runtime but canvas-utils.js should be included (if you want to use Canvas.vsGet() and other utilities).

In VS2008 you should trick the environment by assigning the variable that refers the 2D context to Canvas.vsDoc.Canvas2dContext, by something like this:

var ctx = canvas.getContext("2d");
if (typeof DESIGN_TIME != "undefined" && DESIGN_TIME)
ctx = Canvas.vsDoc.Canvas2dContext;

DESIGN_TIME global variable is defined inside canvas-vsdoc.js. In runtime it should be undefined or false.

Just a note: if you still want to work in IE, you will find this Google extension very interesting: http://code.google.com/chrome/chromeframe/

Update: Visual Studio 11 natively supports canvas intellisense.

 

 

 

 

 

 

Advertisements

Hollywood Principle

Posted in Coding, Development, Internet, JavaScript by Homam Hosseini on December 7, 2009

Today I was working on refactoring some names in Hyzobox In/Out API. It is my personal favorite piece of code in the whole platform. In summary it allows the publisher of the game to customize the game in runtime dynamically by injecting codes and executing some functions in the context of the game (In) and to get notified about the events that are occurring inside the game (Out).

Inversion of Control is very natural in JavaScript and it has been used extensively in In/Out API. It’s quite different from popular prototype pattern but most everyday JavaScript programmers use IoC even though they don’t usually notice it.

Here is a sample in our API:

We register an event listener in Hyzobox, waiting for landing view of the game to be loaded:

var hb = Hyzobox.createInstance();
var landingview_loaded = function(hbEvent) {
   // do something with hbEvent
}
hb.addEventListener('landingview_loaded', landingview_loaded);

It’s is clear that we don’t have control over when landingview_loaded event will be fired and its handler will be called.

hbEvent argument that is of type Hyzobox.Event has a data attribute that is of type Object. In this example the data is a LandingView instance. We can interact with this object in the event handler:

var landingview_loaded = function(hbEvent) {
   var view = hbEvent.data;
   view.inject('a-container-id', 'some text');
};

In this example we are injecting ‘some text’ to an element identified by ‘a-container-id’ inside landing view.

addEventListener() is part of Out and inject() is part of In API. If we want to listen to the events that are occurring inside a particular view, we should register their halnders after the view has been loaded:

var landingview_loaded = function(hbEvent) {
   var view = hbEvent.data;
   view.attachEventListener('playNow', function playNowHandler(playNowHbEvent) {
       // do something with playNowHbEvent
   });
};

And so on, we can have many nested Ins and Outs.

It’s easy to see that in these examples the control has been transferred to the event handlers. The caller raise the events but it’s the responsibility of the handlers to control the functionalities.

I don’t want to go into the the details now, because the work hasn’t yet been finished on these APIs. Once released, we will post them in Hyzobox documentations and Hyzonia tech blog in the following weeks.

Tagged with: , , ,

Accessing Remote ASP.NET Web Services using JSONP

Posted in Coding, Development, JavaScript by Homam Hosseini on October 12, 2009

The problem:

You cannot call remote ASP.NET web service methods from a JavaScript, AJAX client.

Example:

You have a web service, at this address: http://a.com/service.asmx and you’ve configured the service to work with AJAX clients:

[WebService
(Namespace = "http://www.hyzonia.com/gametypes/PopNDropLikeGame/WS2")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.Web.Script.Services.ScriptService]
public class GameService : System.Web.Services.WebService
{
    [WebMethod(EnableSession = true)]
    public GameSessionResponse CreateGameSession(Guid questId)
    {
...
    }
}
}

And it works fine when you call its methods from a web page that is in this address: http://a.com/page.htm:

$.ajax({
        type: "POST",
        url: "GameService.asmx/CreateGameSession",
        data: "{questId: '" + questId + "'}",
        cache: false,
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function(response) {
            Game._onSessionGot(response.d);
        }
    });

But the very same client-side code doesn’t work from this address: http://b.clom/page.htm

The problem in depth:

At first I cannot hold myself and not say that it is a silly problem. web services are meant to be called by remote clients. The fact that browsers block access to web services by AJAX calls is clearly contrary to the purpose of web services.

Interestingly browser extensions like Flash and Silverlight also by default block remote web services, but they provide a work around. Unfortunately no browser by date supports this work around for XMLHTTPRequests. This “security measure” seems odder when we notice that it is perfectly correct to import a JavaScript code snippet from another domain by a script tag:

<script
src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"
type="text/javascript"></script>

 

The solution:

As it was said, Flash and Silverlight both support remote calls. You just need a clientaccesspolicy file to be hosted at the root of a.com (http://a.com/clientaccesspolicy.xml):

<?xml version="1.0" encoding="utf-8"?>
<access-policy>
  <cross-domain-access>
    <policy>
      <allow-from http-request-headers="SOAPAction">
        <domain uri="*"/>
      </allow-from>
      <grant-to>
        <resource path="/" include-subpaths="true"/>
      </grant-to>
    </policy>
  </cross-domain-access>
</access-policy>

This file allows remote calls to be made from any other domain.

But in many situations we want to call the web service methods directly by AJAX clients. This need was the cause of to the development of JSONP (JSON with padding) protocol. As it was discussed it is correct to have a <script> element that loads a script from another domain. On the other hand you may know that it is possible to load scripts dynamically by a simple JavaScript trick (writing<script> tags) or using this jQuery plug in. Now the bulbs are flickering! The solution is to access the JSON web service by the src attribute of a <script> element. This is the whole idea behind JSONP.

But there are a couple of problems needed to be solved for ASP.NET ASMX web services before we can use them in a JSONP scenario.

  1. ASP.NET web services by default only accept POST requests, a <script src=””> element, produces a GET request.
  2. The result of the web method call must conform to JSONP, and you guess, ASP.NET 3.5 by default doesn’t support it.

The solution to the first problem may seem trivial, we can easily enable GET calls to web methods using [ScriptMethod(UseHttpGet = true)] attribute. The immediate problem is that when we mark a web method by this attribute it only can be called by GET requests. And remember, other clients (actually anything other than JSONP clients) are supposed to communicate with the web service by POST requests. I usually end up inheriting from the original web service and marking web methods by [ScriptMethod(UseHttpGet = true)] attribute in the derived class. Therefore I will have two ASMX web services, one using the original class (expecting POST request) and the other using the derived class (expecting GET requests).

[WebMethod(), ScriptMethod(UseHttpGet = true)]
public override GameSessionResponse CreateGameSession(Guid questId)
{
   return base.CreateGameSession(questId);
}

Note you may need to add this code snippet in web.config:

<system.web>
 <webServices>
   <protocols>
     <add name="HttpGet"/>
   </protocols>
 </webServices>
…
</system.web>

There’s another problem to be addressed in the client side. The client should call the web method by a correct URL (it has to pass a correct query string that could be deserialized back to .NET objects in the server side). In case of POST requests, I’m used to JSON2 library to post data to ASP.NET ASMX web services. Jquery $.AJAX method (when it is configured to use JSONP, by dataType: “jsonp”) creates query string parameters for the data object it receives. But the result is not usable for ASMX web services.

Luckily there’s a ready to use JQuery plug in (jMsAjax) that has the required algorithms for serializing a JavaScript object into a query string that can be parsed by ASP.NET web services.

Using the plug in I created this function to serialize JavaScript objects into query strings:

$.jmsajaxurl = function(options) {
    var url = options.url;
    url += "/" + options.method;
    if (options.data) {
       var data = ""; for (var i in options.data) {
       if (data != "")
         data += "&"; data += i + "=" + msJSON.stringify(options.data[i]);
       }
       url += "?" + data; data = null; options.data = "{}";
   }
   return url;
};

You will need jMsAjax for this code snippet to work.

Finally this is a sample of a client side code using JQuery that calls an ASMX web service using JSONP:

var url = $.jmsajaxurl({
    url: "http://hiddenobjects.hyzonia.com/services/GameService3.asmx",
    method: "Login",
    data: { email: "myemail@mydomain.com", password: "mypassword" }
});

$.ajax({
    cache: false,
    dataType: "jsonp",
    success: function(d) { console.log(d); },
    url: url + "&format=json"
});

Or equivalently:

$.getJSON(url + "&callback=?&format=json", function(data) {
    console.log(data);
});

When you call an ASP.NET web service method (that is configured to receive GET requests) using a code similar to the above, it returns in XML. The problem is that the web service expects to receive a request that has a content type of “application/json; charset=utf-8” and <script> element simply doesn’t add this content type to the request. There’s a little thing we can do at the client side. The easiest way to resolve this problem is to use a HTTP module. The HTTP module should add this content type to the requests before they are processed by the web service handler.

On the other hand a JSONP client expects that the web service return the call by a string like this:

nameOfACallBackFunction(JSON_OBJECT_WEB_METHOD_RETURNED)

nameOfACallBackFunction must be given to the server by a parameter in the query string. Different JSONP compatible web services use different names for this parameter, but usually it is named ‘callback’. At least this is what $.ajax() automatically adds to the request in JSONP mode.

I grabbed this HTTP module from a post in elegantcode.com.

public class JsonHttpModule : IHttpModule
{
    private const string JSON_CONTENT_TYPE = "application/json; charset=utf-8";

    #region IHttpModule Members
    public void Dispose()
    {
    }

    public void Init(HttpApplication app)
    {
        app.BeginRequest += OnBeginRequest;
        app.ReleaseRequestState += OnReleaseRequestState;
    }
    #endregion

    bool _Apply(HttpRequest request)
    {
        if (!request.Url.AbsolutePath.Contains(".asmx")) return false;
        if ("json" != request.QueryString.Get("format")) return false;
        return true;
    }

    public void OnBeginRequest(object sender, EventArgs e)
    {
        HttpApplication app = (HttpApplication)sender;

        if (!_Apply(app.Context.Request)) return;

        if (string.IsNullOrEmpty(app.Context.Request.ContentType))
        {
            app.Context.Request.ContentType = JSON_CONTENT_TYPE;
        }
    }

    public void OnReleaseRequestState(object sender, EventArgs e)
    {
        HttpApplication app = (HttpApplication)sender;

        if (!_Apply(app.Context.Request)) return;

        app.Context.Response.Filter = new JsonResponseFilter(app.Context.Response.Filter, app.Context);
    }
}

public class JsonResponseFilter : Stream
{
    private readonly Stream _responseStream;
    private HttpContext _context;

    public JsonResponseFilter(Stream responseStream, HttpContext context)
    {
        _responseStream = responseStream;
        _context = context;
    }

    public override bool CanRead { get { return true; } }

    public override bool CanSeek { get { return true; } }

    public override bool CanWrite { get { return true; } }

    public override long Length { get { return 0; } }

    public override long Position { get; set; }

    public override void Write(byte[] buffer, int offset, int count)
    {
        var b1 = Encoding.UTF8.GetBytes(_context.Request.Params["callback"] + "(");
        _responseStream.Write(b1, 0, b1.Length);
        _responseStream.Write(buffer, offset, count);
        var b2 = Encoding.UTF8.GetBytes(");");
        _responseStream.Write(b2, 0, b2.Length);
    }

    public override void Close()
    {
        _responseStream.Close();
    }

    public override void Flush()
    {
        _responseStream.Flush();
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        return _responseStream.Seek(offset, origin);
    }

    public override void SetLength(long length)
    {
        _responseStream.SetLength(length);
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        return _responseStream.Read(buffer, offset, count);
    }
}

This HTTP module will be applied to each request to a .asmx file that has a format=json in its query string.

Note that you have to update web.config:

<system.web>
…
  <httpModules>
    …
    <add name="JSONAsmx"/>
  </httpModules>
</system.web>

For IIS6 and

<system.webServer>
  <modules>
  …
    <add name="JSONAsmx"/>
  </modules>
  …
</system.webServer>

For IIS7.

Now to test is open your web service in your browser, in my example:

http://hiddenobjects.hyzonia.com/services/GameService3.asmx/Login?email=e@e.com&password=p

It should return in XML

And

http://hiddenobjects.hyzonia.com/services/GameService3.asmx/Login?email=”e@e.com”&password=”p”&format=json&callback=myCallBackFunc

Will return:

myCallBackFunc({"d":{"__type":"HLoginResponse",
"isSuccessful":false,"error":false,"authSessionId":null,"nickName":null,"score":0}});

Don’t worry about myCallBackFunc, JQuery nicely manages it, so that the whole business is behind the scene and you can use $.ajax success callback the very same way you use it for a normal AJAX call.

We should note that JSONP has its own problems, especially… yes… in IE! All versions of Internet Explorer has a 2083 character limit for the URL of a request. It means that you cannot send large data in GET requests to the server. Sometime this limitation leaves us with no choice but to use Flash or create a proxy to the remote web service in the local domain.

Returning Anonymous Types in Web Services

Posted in Coding, Development by Homam Hosseini on July 9, 2009

When coding an AJAX app that makes relatively many calls to the server in short periods of time, the main concern is to minimize the bandwidth it consumes. For example think of an AJAX chat application. For it to look like a real time app we have to query the server every few seconds.

If you’re using .NET, you already knew how easy it is to return objects and have them serialized in JSON in Web Services. All we need to do is to deal with the logics and .NET does all the things and tricks related to the communication. For our example, this is the method that needed to be called periodically from the client:

[WebMethod]

public IEnumerable<ChatMessage> GetMessages()

{

var currentPlayer = OnlinePlayers.Single(p => p.Id == CurrentPlayerId);

var messages = Messages.Where(m => m.DateSent > currentPlayer.DateSynced);

currentPlayer.DateSynced = DateTime.Now;

return messages;

}

The problem is that .NET really serializes everything. If we have the following definitions:

[Serializable]

public class Player

{

public Player() { }

public string Name { get; set; }

public string Id { get; set; }

public string PhotoUrl { get; set; }

public DateTime DateSynced { get; set; }

// other properties

}

[Serializable]

public class ChatMessage

{

public ChatMessage() { }

public Player Sender { get; set; }

public string Message { get; set; }

public DateTime DateSent { get; set; }

}

It is certainly not desirable to send a Player object back to the client by every ChatMessage. Assuming that the client already knows all the Players involved in the Chat, the ChatMessage object that is being sent to the client only needs to have a Sender ID property. One obvious solution that is very familiar for hardcore client-server developers is to have another type, let’s say ClientChatMessage that only contains the required information. If you’re taking this approach remember ClientChatMessage should be a struct type:

[WebMethod]

public IEnumerable<ClientChatMessage> GetMessages()

{

//…

return messages.Select(m => (ClientChatMessage)m);

}

[Serializable]

public struct ClientChatMessage

{

public string SenderId;

public DateTime DateSent;

public string Message;

public static explicit operator ClientChatMessage(ChatMessage m)

{

return new ClientChatMessage()

{

DateSent = m.DateSent,

Message = m.Message,

SenderId = m.Sender.Id

};

}

}

When we are targeting only AJAX clients it’s very handy to return anonymously typed objects. Anonymous objects cannot be serialized by XML serialization, but JavaScript (JSON) serializer is able to serialize them. I prefer it:

[WebMethod]

public IEnumerable<Object> GetMessages()

{

//…

return messages.Select(m =>

new {

s = m.Sender.Id,

m = m.Message,

d = m.DateSent

});

}

Here I’ve shortened the names of the properties, hey it is AJAX, we should save bandwidth by every mean possible.

We’ve used this trick in many places of the games we are developing for Hyzonia, as the current games only will be available for JavaScript clients. We found another similar trick very handy: a web method can take an object as an argument; if you send a JSON serialized object from the client to these methods, you’ll have a Dictionary<String, Object> in the server side.

[WebMethod]
public IEnumerable<ChatMessage> GetMessages()
{
var currentPlayer = OnlinePlayers.Single(p => p.Id == CurrentPlayerId);
var messages = Messages.Where(m => m.DateSent > currentPlayer.DateSynced);
currentPlayer.DateSynced = DateTime.Now;
return messages;
}

JQuery Wingooli Photo Gallery

Posted in Coding, Development, Internet by Homam Hosseini on May 10, 2009

I just want to introduce a JQuery photo gallery plugin I developed fro my profile. My main motivation for building this plugin was that I wanted it to be search engine friendly therefore I needed a clear separation between the photo gallery functionalists and the data describing the photos and the gallery. It is something that is easy to achieve using JQuery.

BTW these days I spend a part of my time discussing and teaching OOP JavaScript to our fellow programmers in RENA. It’s interesting for me to discuss the somewhat weird features of JavaScript for these guys who are already well experiencedand talented .NET developers. I try my best to convince them JavaScript is so fun when you get used to it, so fun and so powerful that you end up you want to kiss all the ASP.NET AJAX and UI functionalists a goodbye and develop the effects yourself and see how much you can improve the performance and the branding of your application.

We in RENA are looking for a Web UI Developer to handle such those tasks, it came out to be a very hard job finding a person for this position, mainly because it requires you to be a JavaScript God! to pass the first step in the recruitment process. Drop us a message if you fit the position.

Tagged with: ,