Reduce coupling with libgdx by extracting shared functionality into a new dependency

[pakoito]

Related:
libgdx/libgdx#2793
http://www.reddit.com/r/gamedev/comments/2u8ytc/gdxai_150_released/co6b3hx

To ease using this library in other projects without bringing the whole graphic library, it'd be nice if it was split into a shared module and the core library,

[tomcashman]

+1 This also gets rid of dependency on specific versions of libgdx. I want to use gdx-ai with mini2Dx but they have conflicting libgdx versions and I have to update mini2Dx to use a matching version.

[davebaol]

@tomcashman
Please add your vote to libgdx/libgdx#2793 too.
It's your best bet to get it sooner or later.

[davebaol]

Ok I'm going to start working on this.
From my analysis gdx-ai has 2 kind of dependencies from libgdx:

• Depencencies that you can fix with just the libgdx.jar (native libraries not required) or possibly a smaller compatibility jar containing only the minimal set of required classes (direct and indirect dependencies)
  • com.badlogic.gdx.math.Vector
  • com.badlogic.gdx.math.MathUtils
  • com.badlogic.gdx.utils.Array
  • com.badlogic.gdx.utils.GdxRuntimeException
  • com.badlogic.gdx.utils.IntMap
  • com.badlogic.gdx.utils.ObjectMap
  • com.badlogic.gdx.utils.Pool
  • com.badlogic.gdx.utils.SerializationException
  • com.badlogic.gdx.utils.TimeUtils
  • com.badlogic.gdx.utils.reflect.ArrayReflection
  • com.badlogic.gdx.utils.reflect.ClassReflection
  • com.badlogic.gdx.utils.reflect.Field
  • com.badlogic.gdx.utils.reflect.ReflectionException
• Depencencies that force you to initialize the libgdx framework, meaning that you MUST have in class path the libgdx.jar with native libraries, not to mention the waste of resources
  • com.badlogic.gdx.Application just for logging
  • com.badlogic.gdx.Graphics for deltaTime between frames and frameId
  • com.badlogic.gdx.files.FileHandle to load a behavior tree form a file

To fix the last set of dependencies I have to change how gdx-ai works internally by adding an abstraction layer.
I think that the service locator pattern should be used here. The locator should get you a LogProvider, a TimeProvider and a FileSystemProvider.
You just have to initialize the service locator with proper providers.
What do you think?

[tomcashman]

Service locator makes sense. I guess there would be something along the lines of Gdx.logProvider, Gdx.timeProvider, etc. to statically access them rather than passing references to everything?

[davebaol]

@tomcashman
Yeah, sure. You won't have to pass the service locator anywhere. You'll have just to initialize it.
Service locator is a decoupling pattern after all.
By the way, regardless of this particular issue It's worth reading the entire book linked above. 😉

[davebaol]

Just realized that most of the times you don't even need to set proper providers on the service locator.
if Gdx.app != null libgdx has been initialized and gdx providers will be set when the service locator class is loaded by the class loader.
If Gdx.app == null libgdx has not been initialized so we can safely assume that gdx-ai is running inside a standalone application and default desktop providers will be set.
Of course if you want to use gdx-ai in Android (or any other non desktop platform) out of lbgdx then you have to implement and set proper providers.

[davebaol]

Ok I got it working with the auto-configuration mentioned in my previous post.
Now non-libgdx applications only need gdx.jar in the classpath (native libraries and libgdx initialization are no longer required).
I'm going to push changes to the repo after some code cleanup.

[erlend-sh]

Awesome! You're welcome to post an update about this on the jMonkeyEngine forum as well once it's ready ;)

[davebaol]

Done!
The snapshot jar is up already.
The wiki page will be updated in the next days.
See CHANGES and ask if you have problems.
Also, notice that now you have to call this at the very beginning of the game cycle

GdxAI.getTimepiece().update(deltaTime);

where deltaTime is the time in seconds since the last frame.
Of course, if the game is paused you don't have to update the timepiece (unless your pause screen needs AI, which is rather unlikely).

Please, test and report 😊

@erlend-sh
Sure, I'll post an update on jMonkeyEngine forum as soon as I get some positive feedback here. 😉

[tomcashman]

Not sure if it's just me or if Timepiece seems like the incorrect terminology here?

Apart from that it looks good, will take it for test run tomorrow :)

[davebaol]

@tomcashman
The timepiece is just a clock that gives you current time and last delta time.
It's needed because some parts of gdx-ai (like for instance message dispatcher, jump steering behavior and wait task) have a notion of spent time and I want to support game pause, so TimeUtils cannot be used here.
When the game is paused you simply don't update the timepiece.

That said, English is not my native language. So If you have a better name I'm all ears of course. 😊

[tomcashman]

It makes sense that it is needed. Maybe Timestep is a more suitable term? Delta is often referred to as the timestep value (e.g. http://gafferongames.com/game-physics/fix-your-timestep/)

[davebaol]

Don't know.
Regardless of whether the timestep is fixed or not, you continuously give the timepiece a delta to update the current time. From the application's point of you it's just a clock. Maybe TimeService ?

[tomcashman]

Good point. Yeah I'd say TimeService or even just Time.

[davebaol]

The problem with Time is, so to speak, the repeated possibly ambiguous getTime()

float currentTime = GdxAI.getTime().getTime();

[davebaol]

New wiki page done.