Game Geek Speak

Whoa. Unity really is going to be omni-platform!

I can’t wait to have a chance to make a web game that I then port to iPhone, Android, and XBox Live Arcade. This kind of thing can’t really be understated for small developers because the best way to maximize your revenue per game is to release it on as many platforms as possible.

Some highlights from the press release:

…major updates to Unity’s rendering capabilities, its physics features and significant optimizations to its core systems… [I hope this means PhysX and Mono upgrades!! Confirmed! Mono 2.6.x!]

Illuminate Lab’s Beast lighting software provides Unity developers with a complete global illumination solution for photorealistic scene lighting.

[Unity iPhone has] a very fast 2D sprite engine…

Global illumination and occlusion culling might be Pro-only features, but it’s still really exciting.

Set for release this Summer. Bring it on!!

I was kind of shocked to hear that Project Darkstar has been shut down, and its staff laid off. My online multiplayer technology strategy was hinging on Darkstar. Major downer!

But I also learned that a couple of the original Darkstar team members, led by Owen Kellett, has forked the code and is trying to keep it alive as RedDwarf. So, that’s a very cool thing. I hope that it does thrive, because Darkstar is a pretty amazing server technology despite the fact that it’s not finished.

I hope all of Darkstar’s users will migrate to the new project and support it. Anyone can contribute code (though there is a sensible review process), so please go make your mark, and save this great server solution from the trash bin of history!

Following on from Angry Explanations #1, we will now add some motion to the scene. For kicks and giggles, we’ll cause the image to rotate each frame.

(Note that this information is in reference to PushButton Engine build r625.)

The key takeaway here is that for a component to be tickable, it must implement the ITickedObject interface and then tell the ProcessManager to start and stop calling onTick() every tick.

Oh, there’s one other key takeaway here: how to use PropertyReferences. You get a property of a component by way of the owning entity. You create a PropertyReference instance for each data member that you need to access. In this example, we’re accessing the rotation field on the SpriteRenderer component we added in Angry Explanations #1.

In a bit more detail, the PropertyReference is constructed with a special string: "@Sprite.rotation" (see line 11 in the code below). That means, this is a reference to the component of this entity with the name “Sprite” (recall that we gave it that name when we created the SpriteRenderer component instance), and the field “rotation” of the SpriteRenderer class. It’s quite simple once you realize what it’s doing (but I’m no less angry, mind you!).

I thought that a SpatialComponent might be necessary to alter the sprite’s position, but apparently that component has been removed (since r470, which is the current packaged release). That data seems to now be handled by the renderer component itself.

Add this one line to the end of showLogo() from the previous example:

spriteEntity.addComponent( new SpinController(), "spinner" );

Then add the following new class in a sub-folder (components/controllers/).

package com.yourcompany.yourgame.components.controllers
{
	import com.pblabs.engine.core.ITickedObject;
	import com.pblabs.engine.core.ProcessManager;
	import com.pblabs.engine.entity.EntityComponent;
	import com.pblabs.engine.entity.PropertyReference;

	public class SpinController extends EntityComponent implements ITickedObject
	{
		// Cache the PropertyReference instance here to avoid a bunch of temporary allocations.
		private var _rotProp:PropertyReference = new PropertyReference( "@Sprite.rotation" );

		// Nothing to do in the constructor because this is such a simple example.
		public function SpinController()
		{
			super();
		}

		// When the component is added to the sprite entity, we want to register to
		// get tick updates by the ProcessManager.
		protected override function onAdd():void
		{
			super.onAdd();

			ProcessManager.instance.addTickedObject( this );
		}

		// When the component is removed from the sprite entity, we want to unregister
		// from the ProcessManager so tick updates will stop.
		protected override function onRemove():void
		{
			super.onRemove();

			ProcessManager.instance.removeTickedObject( this );
		}

		// Each tick, we just change the rotation of the sprite renderer a little bit.
		public function onTick(tickRate:Number):void
		{
			// Get the current rotation.
			var rotation:Number = owner.getProperty( _rotProp ) as Number;

			// Add 1 degree to it.
			rotation += 1;

			// Store the new rotation back in the sprite.
			owner.setProperty( _rotProp, rotation );
		}
	}
}

As an addendum, I should point out that the rotation will probably not be smooth. To fix that, you should have the SpinController implement IAnimatedObject instead of ITickedObject. The registration with the ProcessManager is the same, except you call addAnimatedObject() instead of addTickedObject().

The difference is that IAnimatedObject will update when Flash draws a frame instead of when the ProcessManager ticks, and the motion will appear a lot smoother.

And you’ll want to normalize the rotation based on delta time since the last frame. Er, like this:

public function onFrame( elapsed:Number ):void
{
	var rotation:Number = owner.getProperty( _rotProp ) as Number;

	// Rotate 15 degrees per second, nice and slow.
	rotation += 15 * elapsed;

	owner.setProperty( _rotProp, rotation );
}

(Thanks to Ben G. for that humorous title! And just to be super clear–I’m not angry at all about PBE. The anger is entirely tongue-in-cheek.)

So, yeah, I got started with PBE at a bad time, I think.

It’s in transition between some major changes, and so all the docs and tutorials to this point are out of sync and kind of very… confusing. Because of that, I really struggled to figure this out, and in fact couldn’t get an image on the screen without professional help (I’ll let you interpret that however you’d like).

This information is relevant for PBE r625 and up.

(This isn’t to say the engine is poorly designed–it’s simply not accurately documented in places because it has been changing so quickly. And to be fair, it’s still in beta. I wouldn’t use the engine if I didn’t think it was great.)

A frustrated noob’s guide to getting a freakin’ image on the dang screen using Flex 3

Here’s the MXML which will reference the code.

<?xml version="1.0" encoding="utf-8"?>
<game:Game
	xmlns:mx="http://www.adobe.com/2006/mxml"
	xmlns:game="com.yourcompany.yourgame.*"
	width="750"
	height="600"
	layout="absolute">

</game:Game>

Now define a resource in a ResourceBundle subclass, which is the image you want to display, and let PBE automagically make it accessible through the resource manager.

package com.yourcompany.yourgame
{
	import com.pblabs.engine.resource.ResourceBundle;

	public class EmbeddedResources extends ResourceBundle
	{
		// The path is magically also the name of the resource.
		[Embed(source="../assets/images/logo.png", mimeType="application/octet-stream")]
		public var logoImage:Class;
	}
}

Put that image into action! It’s a simple notion, but somewhat complicated if you’re new to the engine and its gooey innards.

package com.yourcompany.yourgame
{
	import com.pblabs.engine.PBE;
	import com.pblabs.engine.entity.IEntity;
	import com.pblabs.engine.resource.ImageResource;
	import com.pblabs.engine.resource.ResourceManager;
	import com.pblabs.rendering2D.DisplayObjectScene;
	import com.pblabs.rendering2D.SpriteRenderer;
	import com.pblabs.rendering2D.ui.FlexSceneView;

	import mx.containers.Canvas;
	import mx.core.Application;
	import mx.events.FlexEvent;

	public class Game extends Application
	{
		public var resources:EmbeddedResources;

		// We need access to this in a couple of functions.
		private var _scene:DisplayObjectScene;

		public function Game()
		{
			super();

			// Let the Flex Application initialize fully before we muck with it.
			addEventListener( FlexEvent.APPLICATION_COMPLETE, onStartup );
		}

		// This is called once the Flex app (stage, in particular) is initialized.
		private function onStartup( e:FlexEvent ) : void
		{
			// Load our embedded resources (the image to show).
			resources = new EmbeddedResources();

			// Tell PBE to initialize and pass it our instance so it can get the stage.
			// (Remember, Application is a subclass of Sprite, which PBE needs.)
			PBE.startup( this );

			createPbeScene();

			showLogo();
		}

		private function createPbeScene():void
		{
			// Create a new IEntity for the scene view.
			var sceneEntity:IEntity = PBE.allocateEntity();
			sceneEntity.initialize( "sceneEntity" );

			_scene = new DisplayObjectScene();

			// Since this is Flex, we need the appropriate scene view class.
			var sceneView:FlexSceneView = new FlexSceneView();

			// Set up the view size.
			sceneView.width = 750;
			sceneView.height = 600;

			// FREAKIN' IMPORTANT: add the view as a child to our display list!
			this.addChild( sceneView );

			// Connect the view to the display object scene (a component).
			_scene.sceneView = sceneView;

			// Add the display object scene to the scene entity.
			sceneEntity.addComponent( _scene, "renderer" );
		}

		private function showLogo():void
		{
			// Create a new IEntity instance for the sprite to be displayed.
			var spriteEntity:IEntity = PBE.allocateEntity();
			spriteEntity.initialize( "logoEntity" );

			// Add a sprite rendering component.
			var sprite:SpriteRenderer = new SpriteRenderer();

			// Tell the renderer to draw (and load) this image resource.
			sprite.fileName = "../assets/images/logo.png";

			// Tell the renderer to draw to the display object scene.
			sprite.scene = _scene;

			// Add the component to the sprite entity.
			spriteEntity.addComponent( sprite, "sprite" );
		}
	}
}

So, what the heck just happened? Pfft! Don’t ask me! I’m still a freakin’ noob!

I know a couple of things, though. The SceneView is like a “canvas” where all DisplayObjectRenderers are drawn. So you create entities and fill them with components (like a SpriteRenderer) and tell the renderer component about the scene view. Magically, the sprite appears! It’s not too much to understand if you just want to know the API and how to use it.

To really understand it, you’ll need to look under the hood and figure out the connections. A good bit of hidden work is being done to simplify the API, but possibly at the expense of understanding. It’s neither good nor bad. It’s just The Way of PBE (for now).

Feel free to post here to help fill my gaps in comprehension. I haven’t used the engine enough to write a thorough explanation, and I’m not too proud to accept help.

John from the Darkstar forums (and project team member? I’m not sure), has posted a short video of Keith Thompson (one of the Project Darkstar Server engineers) showing a demo at 2009’s Austin GDC. The video is a bit hard to watch if you’re sensitive to shaky motion, but it’s worth it if you’re a big enough geek, like me.

Apparently, the Snowman demo game is running on two servers, and the load can be dynamically managed so that if one server reaches a limit, clients will be moved onto the second server. Interestingly, this means both clients that are logging in and clients that are already in the middle of a game. The load is balanced transparently by Darkstar, with clients continuing without a hitch.

Looks like they also have some decent monitoring tools. I wonder if those will get released to the community?

I wish them all the best, because I’m using Darkstar for most (possibly all) of my future games. Go Darkstar team!!

The microtransaction bug seems to be going viral these days among the Flash community. There are a growing number of companies offering managed payment services to Flash developers: they handle the dirty backside, and you give them content and share the income.

I personally think that it is worth it to build your own system (and I’m usually the guy saying, “Use the middleware, fool!”). But I think it depends on the scale of what you are planning. In my case, I want total control, and I want to own access to my customers so that I can continue to communicate with them. I also don’t want my games to become advertisements for a payment service.

I don’t view virtual item sales as just a sales channel. It’s also a gesture that means a player cares about and is emotionally invested in the game, and I want to maximize that relationship to make my players happy, long-term customers. Without access to my customers, the payment service is crippling my business. I don’t know that all these systems insulate the developer from his/her customers, but that is a major issue to bear in mind.

These Flash-specific services could be really useful to someone who is making much smaller scale games and wants some add-on sales or someone experimenting with virtual goods in an effort to diminish reliance on ad revenue. I’m not reviewing any of the services, just announcing that they exist. I haven’t investigated them all very deeply, but I will be poking around.

75% – andrograde.com
70% – www.nonoba.com
60% – www.gamersafe.com
60% – www.mochimedia.com
50% – www.heyzap.com

Which is best? It depends on your goals and plans. If you’re just making little quickie games (90% of Flash games), then any of the above would work. If you have a more broadly scoped business plan, you might want to steer clear and look into services that are not Flash-specific and spend the time/money to do the integration yourself.

Java’s ‘instanceof’ keyword is not the same as ActionScript’s ‘is’ keyword. In theory, they do the same thing: find out if an instance of an object implements a class or interface. In reality, they’re quite different.

Java compares for an exact match. ActionScript compares for a match or any subclass of the class being compared.

Let’s say we have class A which implements interface I. And we have class B which is a subclass of A (and implicitly implements interface I).

Java:

if( A instanceof I ) // True
    print( "yeah" );

if( B instanceof A ) // True
    print( "yeah" );

if( B instanceof I ) // False!
    print( "yeah" );

ActionScript:

if( A is I ) // True
    print( "yeah" );

if( B is A ) // True
    print( "yeah" );

if( B is I ) // True!
    print( "yeah" );

So, having learned a lot of ActionScript before diving into Java, I expected ‘instanceof’ to behave just like ‘is’. But no. And that was annoying not to realize at first. So, you’ve been warned!!

Update: Hmm, now I wonder if overloading method parameters behaves the same way as instanceof in Java? I’m going to be safe and make an interface for any classes that have multiple subclasses (ie, categories of entities which require special behaviors). It’s still polymorphic, so I guess it’s “good design.” I haven’t had quite enough experience digging into the reasons for Java’s language design choices.

Update 2: Of course I had to test the behavior of overloaded methods. Turns out that Java isn’t as exacting with overloaded methods–which is a relief!

For example, I have an Entity class, and a subclass called ItemEntity. I need to do some special handling on an ItemEntity (or any subclass of it) in a method that takes Entity as a parameter. Overloading that method to take an ItemEntity gives me the desired behavior for ItemEntity or any subclass of ItemEntity. Yay!

I’ve just finished building my client/server communication loop for Spirits of Gaia. The client is Flash (Flex), and the server is Java (built on Project Darkstar).

Darkstar uses a binary message format, which is a different approach from something like SmartFox, which uses strings (“raw”, XML, or JSON). I had experience with SmartFox, but I hadn’t tried to implement a binary format in Flash before. It really wasn’t bad in the end, and most of my time was spent just learning about ByteBuffers and ByteArrays in ridiculous amounts of detail.

And–of course–one of my bugs probably induced more research than necessary as I attributed malfunctions to various other possible causes. The bug was that I inherited one of the command processing classes from a base class which didn’t implement what I thought it did, so it was silently failing. But I learned a lot. A whole fricken lot! And that’s enough learning for anybody.

So one issue is that you can’t be sure what the endian-ness is for the server or the client. Well, maybe you can, but before now I didn’t know enough about it to make any assumptions. Darkstar uses ByteBuffers to hold incoming messages, and the default for Java is big endian for ByteBuffer. Thus, I use big endian on the server.

I had a feeling that Flash would take care of it for me, but of course I wanted to make sure it was using big endian, too. For a while, though, I didn’t know how to make a ByteArray use big endian or little endian.

My first approach was to get around it entirely by encoding all values that require more than 1 byte into hex strings. What a joyful aside that was! (Sarcasm, you see.) I mean, now I know how to encode anything to hex and back and do it sideways, too. But, this wasn’t working so well and it was bloating the nice binary format anyway. (No, I wasn’t really concerned about the size of the packets based on that, but if there’s a better way and it’s more space efficient–why not?)

Then I dug a bit deeper and realized that you can tell a ByteArray to use big endian like this:

var buffer:ByteArray = new ByteArray();
buffer.endian = Endian.BIG_ENDIAN;

Hard, huh? So then I didn’t need to encode multi-byte values into fun hex strings anymore (with one exception). So my PacketBuffer class got a bit more efficient in speed and size, and all is well now.

The one exception is for Java long values, which are 8 bytes. Flash (as far as I know) has no way to pull an 8-byte value from a ByteArray. And, no, I don’t want to do it by hand–which doesn’t mean I won’t! If encoding to hex string doesn’t work out, then I’ll write some code to stitch 8 bytes into a long value and stuff that into a Number (since it won’t fit into a 4-byte int). But, honestly, that kind of stuff is not my cup of tea because it’s not fun to me. But if it’s gotta be done, I’m a professional, so I’ll buckle down and do it. Clearly, I want to whine about it a lot just in case I do really need to do it.

For completeness, you tell a Java ByteBuffer to use big endian like this:

final ByteBuffer buffer = ByteBuffer.allocate( someSize );
buffer.order( ByteOrder.BIG_ENDIAN );

I think it’s ok to assume that Java (and Darkstar) will still default to big endian on whatever OS my future game server will be running (a flavor of Linux, no doubt). If I run into some bizarre bug where command ids are getting scrambled, I’ll know the first place to look.

Well, I’ve spent a lot of time with Project Darkstar. I put in tens of hours reading forum posts and anything else I could get my hands on. I built a very simple MUD with it, and I looked through a bunch of other people’s code. When Darkstar delivers, it will be really amazing, and what exists today is already very cool. It offers solutions to some monstrously difficult problems.

Probably the best thing I found was that you can treat your game logic like a single threaded application. You never have to touch locks or synchronization unless you go under the application layer (a place I feared to tread).

The data store is also really cool, because you can stop worrying about game crashes and if that will force you to roll back hours of gameplay–it won’t. At most, a few seconds are lost. That’s a huge worry out of the way. One problem here, though, is that there’s no easy way to upgrade or patch the data store unless you wipe it and restart from scratch. You’ll have to write a custom tool to update it without wiping it.

All that said, the real issue holding Darkstar back right now is that it simply isn’t finished. It’s almost finished (give it 6 more months), but there’s one key feature that is a show stopper for me: it doesn’t scale. It can’t do anything besides a single-node right now. If you run multi-node, each node will be isolated, which is the same end result.

This really disappoints me, because the technology is otherwise really powerful, and I like it a lot. Sometime near the end of 2009, the roadmap says the PDS team will have multinode completed. When that happens, Darkstar will finally be a very potent game server solution! And I’ll be going back to it.

Until then, what next? I’m going to look into the Neutron service from Exit Games. (Update: After some deeper digging, I don’t think this is what I’m looking for, although I will still give it an eyeball. It also feels like it’s going to be on the expensive side.)

(Update 2: After some pacing around the house and thinking, I have come up with a couple of options for how to continue to use Darkstar for my upcoming game. I haven’t decided exactly what path to take yet, but I think it will be worth it to try and make it work. I’m counting on you, Darkstar team!! )

I’ve been intensely researching Project Darkstar Server (PDS). Along the way, I thought I would collect some of the documentation, forum posts, and tutorials that have helped me understand how to get started. I’ve tried to avoid outdated stuff and only post things relevant to the latest Darkstar (0.9.9 0.9.10 0.9.11). Over time, I will add more as my own knowledge and experience deepens.

So, I present to you A collection of valuable links and resources for finding your way through the Darkstar code thicket.

Getting Started

You’ll need to understand this before you even get started.

• FAQ
• Darkstar overview (PDF)
• Architecture diagram (PDF)
• Coding Darkstar Games presentation slides (PDF)
• Some projects built on Darkstar (clients, tools, etc.)

Server

• Official server tutorial (PDF)
• Server API documentation
• Authentication protocol
• Darkstar compared to Electroserver/SmartFox Server

Example Clients

• Official (Java) client tutorial (PDF)
• A Flash client implementation (PDF)

Darkstar Basics

• The mighty Seth and Owen wrote a framework called Slipstream and an accompanying document (PDF) which is invaluable for learning.
• Configuring logging output and more about Java logging
• Understanding the communications model (client/server direct and channels)
• Channels, sessions, listeners
• JavaOne 2008 MUD tutorial (useful, if somewhat dated)
• JavaOne 2009 Project Snowman tutorial, which is a 3d multiplayer game. Very useful! It’s been said that this game was handling 3000 clients on a single server node.
• To partition the world, or not?
• Server side physics, or not? Or something in between?
• Discussion on how clients talk to each other and the server. Interesting thoughts about latency hiding if you haven’t been exposed to the kinds of issues multiplayer programming presents.
• An insightful discussion which reveals a lot about Darkstar performance tuning and profiling.

Understanding Managed Objects

• Serializable properties of managed objects (MOs)
• Static data in a multi-VM environment and when it might be ok to use static data (and a bit quicker to the point than the first previous link).
• When/why managed tasks
• Managed objects in relation to storing persistent player data
• World representation and data transfer

Understanding Tasks

• Task and scheduling tasks
• When/why managed tasks (repeated since it’s relevant to MOs and Tasks)
• Task-based updates instead of inner loops
• Reactive (event-based) updates instead of polling update loop
• More on being reactive instead of polling
• Monitoring task execution and failures using logging output

Services and Managers

• RPC under Darkstar
• Writing your own service

Protocols and Transports

• Using the pluggable transport/protocol layer (may assist your initial understanding)

Known Issues (Big Ones)

• Time gap when the server shuts down and restarts This is resolved in PDS 0.9.11!
• Difficulties patching a live server
• More discussion about overcoming issues updating live servers

Vital Tools

• Gamalocus profiler and viewer – really useful, and the graphical viewer makes interpreting the data much easier. It hasn’t been updated in a while, so I hope the project owner keeps it up to date or it can be given a new maintainer.
• Asynchronous task library – if you need to do anything outside of Darkstar (like access a database), you will probably want to use this to work outside the Darkstar task time limitation. (I wish this was on Google code. The Java.net site is really horrible [and slow for me] by comparison.)
• MockSGS – a unit testing library for Darkstar.