SpriteKit on Xamarin.iOS: fun without compromise

TL;DR: get the source of the game on github.

With the release of iOS7, and same day support in Xamarin.iOS, I'm spending all my free time playing with the new APIs. I particularly love iBeacon and Background Fetch. Next on my list was SpriteKit.

SpriteKit is a 2D game engine, not unlike cocos2d at all. We'll see next that it's going from one platform to another is very simple.

 I'm not a game developer, but I have some experience with cocos2d as I co-wrote (with Miguel) the cocos2d bindings for Xamarin.iOS. At that time, to test the binding, I ported a sample platform jumper game from obj-c cocos2d to c#. And I again ported the same game to SpriteKit. Here are my findings about the experience:

The Pros

• you can almost to a line by line port between cocos2d and SpriteKit, once you figure out the basics
• less boilerplate. Or even no boilerplate at all with SpriteKit. a SKView is a UIView, and is ready to serve as soon as you PresentScene() it. Compare that with the directors you have to put in place before writing a line of game logic in cocos2d. It's a win.
• less leaky abstractions. I haven't compared performances, but SpriteKit doesn't expose stuffs like BatchNodes, so it's one stuff you don't have to bother about.
• SKAction is a nice addition for objects you don't want to animate yourself in your Update() loop (they're executed just after Update(), and before physics simulation)

The Cons

• I found myself looking for BitmapFonts. It seems like a standard in game development, but missing from SpriteKit (or I haven't found it). I'm quite confident that's a stuff we'll see in an upcoming new version.

The Rest

• As the original game, this port doesn't leverage any Physics engine, so I have nothing to say about SKPhysics* stuffs. From the API, it looks very similar to what Chipmunk offer.

So it was a very pleasant port, at the end taking even less lines of code than the original port, and only 2 hours to write. If you want to start developing games, going for SpriteKit on Xamarin.iOS is really a no brainer. No boilerplate, no gotchas, just fun.

The Code

The code is on github, it's MIT/X11 so do whatever you want with it. The graphics are borrowed from the original game, read the LICENSE about their usage.

Xamarin.iOS 7 : iBeacons - Part 1: Advertizing

One of my favorite new feature of iOS 7 is the addition of iBeacons. You'll find plenty of articles explaining how it'll change the way you do shopping (if you still shop offline), allows indoor localization, and even more. Glue a beacon on your kids, and you'll know when they go too far away (digital leash). Attach one to your wallet and your phone will tell you you're leaving the house with no cash. Applications are endless.

iBeacons is a protocol on top of Bluetooth LE (Low Energy, also advertised as Bluetooth Smart, and part of the Bluetooth 4.0). It doesn't require any new hardware and is nothing really new by itself. What's new and exciting is its position in iOS: first-class citizen, integrated with CoreLocation, working in the background, ...

The recipe: advertising your position

As of now, the only objects you can use as iBeacons are iOS devices. The protocol should be made available soon, allowing 3rd party components to appear, and at that time they should sell for a few dollars a piece (based on a general purpose BT chip, like the BLE112, a beacon should cost around 40$ to build. Prices will surely drop by using cheaper and specialized chips).

Turning your iOS device into a beacon is really only a few steps:

1. Initialize a CLBeaconRegion

That'll be your beacon. uuid and identifier are mandatory. Major and minor are optional. There's a trick here, uuid doesn't have to be unique. All beacons of a common group will probably have the same uuid, and different major/minor versions.

var beaconId = new NSUuid ("5a2bf809-992f-42c2-8590-6793ecbe2437");  //uuidgen on MacOS, nguid in VS
var beaconRegion = new CLBeaconRegion (beaconId, "yourOrg.yourBeacon");

2. Initialize a CBPeripheralManager

var peripheralManager = new CLPeripheralManager (new PeripheralManagerDelegate(beaconRegion), DispatchQueue.DefaultGlobalQueue, new NSDictionary ());

class PeripheralManagerDelegate : CBPeripheralManagerDelegate
{
    CLBeaconRegion beaconRegion;

    public CBPeripheralManager (CLBeaconRegion beaconRegion)
        this.beaconRegion = beaconRegion;
    }

    public override void StateUpdated (CBPeripheralManager peripheralManager)
    {
        //State will be Unsupported on devices like iPhone4 and prior, PoweredOff if BT is down
        if (peripheralManager.State != CBPeripheralManagerState.PoweredOn)
            return;
        var options = beaconRegion.GetPeripheralData (null);
        peripheralManager.StartAdvertizing (options);
    }
}


And that's it.

Notes and further reading

• As devices BT ids changes from time to time, your device will be sometimes advertised twice. That won't happen with real iBeacons.
• If you want to advertize in the Background, enable "Acts as Bluetooth LE accessory" in your info.plist
• Read Region Monitoring if you need more details.

It's all about monkeys

Yesterday evening, May 7, two belgian user groups,  MADN and DotNetHub invited me to give a 2 hour introduction session on creating multi-platforms mobile applications in c# with Xamarin 2.0.

Microsoft Belgium was hosting the session, and the room was packed !

I really enjoyed that evening, and just wanted to thank you all: attendees for their presence and interactions, MADN and DNH for the invite and the bottle of wine, Microsoft Belgium for the place, food and drinks, and Xamarin for the give away licences, monkeys and t-shirts.

Decorating your Xamarin.iOS code with Behaviors

Note: this is the post in which I'm getting out of the closet and make it clear that I had an affair with Silverlight. I'm still thinking about it sometimes, and when I do, this is what happens...

Every time you have to ask your user "What's your favourite colour" or "What is the air-speed velocity of an unladen swallow?" from within your iOS application, you have to ask yourself "Wait, will the field still be visible with the virtual keyboard displayed ?"

I don't know how you do it (experience sharing is welcome), but me, I do it this way:

public override void ViewDidLoad ()
{
 base.ViewDidLoad ();

 //Set Bindings and Commands
 placeField.Bind (ViewModel, "Place");
 sendButton.Command (ViewModel.SendCommand);
 busyIndicator.Bind (ViewModel, "IsBusy");

 //Slide the view on keyboard show/hide
 placeField.EditingDidBegin += (sender, e) => {
  UIView.BeginAnimations ("keyboardslide");
  UIView.SetAnimationCurve (UIViewAnimationCurve.EaseInOut);
  UIView.SetAnimationDuration (.3f);
  var frame = View.Frame;
  frame.Y = -100;
  View.Frame = frame;
  UIView.CommitAnimations();
 };

 placeField.EditingDidEnd += (sender, e) => {
  UIView.BeginAnimations ("keyboardslide");
  UIView.SetAnimationCurve (UIViewAnimationCurve.EaseInOut);
  UIView.SetAnimationDuration (.3f);
  var frame = View.Frame;
  frame.Y = 20;
  View.Frame = frame;
  UIView.CommitAnimations();
 };

}

Blogging on topic

A pile of reblochon (get closer, you can smell them)

Producing Better Bindings: Completeness

Note: like the previous post, this one is a follow-up on a series written by someone else. We're all building on top of giant's shoulders. My giant today is Sébastien Pouliot from Xamarin. Read his series Producing Better Bindings.

Second Note: if you're reading this from a news aggregator, you might miss the embedded gists. Read the original there.

I'm lately enjoying writing bindings for Xamarin.iOS and Xamarin.Mac, a lot for the fun, very little for profit. The biggest project by far was creating a managed bindings for cocos2d (v2). This library is huge (~2500 public methods), and the API is far from being fixed in stone. The library is so big that at some point I just gave up, until Miguel resumed the effort during end-of-year break.

Await in the Land of iOS - Collisions in Chipmunk

Note: this blog post follows the ones of Frank Krueger about the alpha release of mono 3.x for Xamarin.iOS bringing .NET 4.5 features to the mobile world: Drag-n-drop and Scripting Users. Read that first, it's worth it.

The old way!

If you're using the Chipmunk bindings, the correct way to handle collisions between shapes is to register 4 (FOUR!) handlers for the different steps: begin, preSolve, postSolve and separate. Your collision handling logic is then spread in 4 different functions. All of that for the same collision.

Working around the reverse callback limitation on Xamarin.iOS

There's one annoying technical limitation of Xamarin.iOS if you have to pass a C# delegate instance to unmanaged code. It's not new, and it's well documented.

But still, having to flag the callback with an attribute and no instance method makes an API hard to use if you don't care that much about the internals of the library you're consuming.

I'm currently polishing the Chipmunk binding for Xamarin.iOS, and the cpSpace has some functions taking callbacks, like cpSpaceEachBody or cpSpaceAddPostStepCallback.

Chipmunk bindings for MonoTouch

(c) S. Delcroix 2013

I'm quite pleased to announce the availability of Chipmunk bindings for monotouch. I started that last year, and bound just enough of it to get a sample working, added some constraints lately in order to place labels, and completed it since for the beauty of the task. The image next to this is a screenshot from a system using a motor, a gear joint, pivot joints and some more.

At this point in time, the ~2000 lines of manually crafted lines of code can be found in this pull request, but you probably won't have to wait long before it's merged in the monotouch-bindings repository.

Our business app doesn't need your game development skills (using damped springs to place labels on a map)

The problem

Positioning labels on a map, a chart, a plan is a problem every UI developer face at one time or another if he has the chance to work on rich business app. This problem is NP-Hard for non-trivial cases. I faced that issue twice. First while building a silverlight charting library, and then very recently for positioning labels around a pin on a plan. This post isn't about how we solved those two cases. For the charting problem, we went for an algorithmic solution which was working but not optimal. For the second, I don't know how they solved it as I didn't took the job.

C++ bindings for monotouch using SWIG

(c) S. Delcroix 2013

I love bindings. I've always loved them. Back in the days, I was binding gtk+ and other gobject libs to C# for fun and f-spot usage. Then I bound some obj-C libs to monotouch for a client and some for pleasure.

But last week I faced something new. I wanted to bind (for monotouch) a C++ iPhone lib for which I only received the binaries and the headers files. The component was too large to even think about doing a manual C glue code. I googled about the possible solutions and the only valuable advice was to use SWIG, without any rationale or tutorial. This is then probably a first. An explanation on why SWIG can help you for this, the problem I ran into and the solutions I found.