LibGDX Tutorial 2: Hello World

26. September 2013

 

There is an old law, possibly predating the age of man, that all tutorials must start with Hello World.  I am nothing if not law abiding, so therefore let’s create a Hello World app.  Hello World is generally one of the simplest programs you can create, you simply display the words Hello World on screen.  Of course, there are always complications in life… that’s what makes it interesting!

 

To get started I created a simple project using the Project Setup tool we discussed in the prior tutorial.

 

We are going to jump in with the code in a second, but first let’s take a quick look at the code created by the project tool, gdx-setup-ui.  Your project should look like this:

image

 

Obviously your file names will vary depending on what you used during the project setup tool.  The key thing to note is the basics of how code is laid out.  The non-suffixed folder ( hello-world ) is where the shared code goes.  The –android, –desktop and –html folders are where platform specific code goes and hopefully you will have minimal need to use these.  I will look at them a bit closer in a few minutes, but for now it’s the file HelloWorld.java that we are interested in.  This is where a very important class called an ApplicationListener is implemented.  Here is the code I used:

 

package com.gamefromscratch.helloworld;

import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.graphics.g2d.BitmapFont;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;

public class HelloWorld implements ApplicationListener {
    private SpriteBatch batch;
    private BitmapFont font;
    
    @Override
    public void create() {        
        batch = new SpriteBatch();    
        font = new BitmapFont();
        font.setColor(Color.RED);
    }

    @Override
    public void dispose() {
        batch.dispose();
        font.dispose();
    }

    @Override
    public void render() {        
        Gdx.gl.glClearColor(1, 1, 1, 1);
        Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
        
        batch.begin();
        font.draw(batch, "Hello World", 200, 200);
        batch.end();
    }

    @Override
    public void resize(int width, int height) {
    }

    @Override
    public void pause() {
    }

    @Override
    public void resume() {
    }
}

 

The first thing you may notice is… there’s no Main!  Well there is one and we will take a look at it in a second.  At the end of the day though, LibGDX is an event driven engine.  You implement an ApplicationListener and GDX calls a number of functions that you can respond to.  The render() method will be called each from, so if you want to, you can think of that as your event loop.  Otherwise there are functions that are called in response to various events, these include create, resize, pause and resume.  I imagine you can guess what event each one is in response to!

 

The bulk of our code is in create() and render().  In create() we allocate a new SpriteBatch, BitmapFont and set the font to the colour red.  SpriteBatch’ing is a common activity in 2D game engines built over 3D libraries, if you’ve used XNA you are used to it.  Basically behind the scenes, LibGDX is using OpenGL ( or WebGL depending on platform ) to do the rendering.  In OpenGL there is a fair bit of overhead in drawing … well, anything.  A spritebatch combines them all into a single operation to reduce the amount of overhead.  In a nutshell, it makes 2D rendering a great deal faster.  A BitmapFont is exactly what it sounds like, a 2D bitmap containing all the characters.  If you don’t specify a Font in the constructor, you will get the default font Arial-15 included with LibGDX.  The font file looks like this:

 

image

 

In the render() method we clear the screen to white by making the OpenGL function call glClear() and glClearColor().  The parameters to glClearColor are the red, green, blue and alpha ( transparency ) values to clear the screen with.  The function glClear actually clears the screen.  As you can see, the underlying OpenGL functionality is exposed in Gdx.gl, although generally you wont work at that level very often.

 

Next we start our sprite batch by calling begin(), then render our text to the batch using the font.draw method.  The parameters to draw() are the batch to draw to, the text to draw and the x and y coordinates to draw the text at.  If you run this code ( right click hello-world-desktop and select Run As->Java Application ) you will see:

 

image

 

Voila!  It’s Hello World.

 

One important thing to be aware of is the project hello-world is not an application that you can run, its a library used by the other projects.  I’ll show you what I mean, take a look at code in hello-world-desktop for example:

image

 

Hey look, it’s Main!  Let’s check out the code:

 

package com.gamefromscratch.helloworld;

import com.badlogic.gdx.backends.lwjgl.LwjglApplication;
import com.badlogic.gdx.backends.lwjgl.LwjglApplicationConfiguration;

public class Main {
    public static void main(String[] args) {
        LwjglApplicationConfiguration cfg = new LwjglApplicationConfiguration();
        cfg.title = "hello-world";
        cfg.useGL20 = false;
        cfg.width = 480;
        cfg.height = 320;
        
        new LwjglApplication(new HelloWorld(), cfg);
    }
}

 

This is the actual entry point for your application, or at least it is for the desktop target.  This is where the Desktop specific configuration happens.  You then start your game off by creating a LwjglApplication object, passing in an instance of your ApplicationListener as well as the Lwjgl specific configuration settings.  If Lwjgl is new to you, it’s a Java based game wrapper over top of OpenGL and is what LibGDX uses for desktop rendering.  Beyond configuring it here, you will have no other interactions with it, LibGDX takes care of all of that for you.

 

To really understand how cross platform magic works in LibGDX, let’s also take a look at the Main for the –html project.  In this case it’s not actually called Main, but instead GwtLauncher.java.

 

image

 

Gwt stands for Google Web Toolkit, and it’s a technology Google provides for compiling Java into JavaScript for use in a browser.  It’s the secret sauce that LibGDX uses to make your game run in HTML.  It’s also horrifically annoying at times, you have been warned!  That said, if you dont care about HTML, you can remove this project completely and save yourself a number of headaches. 

 

Let’s take a look at GwtLauncher.java:

 

package com.gamefromscratch.helloworld.client;

import com.gamefromscratch.helloworld.HelloWorld;
import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.backends.gwt.GwtApplication;
import com.badlogic.gdx.backends.gwt.GwtApplicationConfiguration;

public class GwtLauncher extends GwtApplication {
    @Override
    public GwtApplicationConfiguration getConfig () {
        GwtApplicationConfiguration cfg = new GwtApplicationConfiguration(480, 320);
        return cfg;
    }

    @Override
    public ApplicationListener getApplicationListener () {
        return new HelloWorld();
    }
}

Look’s a lot like the –desktop project main doesn’t it?  The basic concept is exactly the same, you create the platform specific configuration bits, and create an instance of your ApplicationListener.  The GwtApplication class is callback based however, so it looks a bit different.  Once again, you should rarely be working at this level.  One important thing to note though is the values being passed to GwtApplicationConfiguration… this represents the size of the HTML canvas being created.  So if you want your HTML app to be more than a small square in the middle of the screen, this is where you change it.

 

So basically LibGDX works by having you create a single common library that implements your game in a cross platform way in the form of an ApplicationListener.  To support multiple platforms, you have a project for each platform where you create a platform specific application ( an instance of GwtApplication in the case of HTML targets, LwjglApplication for desktop targets, AndroidApplication for Android targets, Application for iOS targets… not shown because I am working on Windows currently ) , configure it and pass in the ApplicationListener.  It is this application class that will be calling back to your ApplicationListener each frame.  The nice news is, most of the time, you wont care about any of this… but it’s handy to understand what’s happening behind the curtains.

 

 

Oh yeah… about GWT

 

Remember I said it was a bit of a pain?  Well let’s take a look at what happens when you run the hello-world-html application ( right click hello-world-html->Run As->Web Application):

 

image

 

 

Ugh…  so basically our code is trying to do something GWT does not permit.  If we flip back to Eclipse in the Console panel we can get a bit more insight into the nature of the exception.

image

 

It’s line 17 in HelloWorld.Java that is causing the exception:

        font = new BitmapFont();

So, what exactly is going on here?  Well, remember earlier when I told you that BitmapFont’s default constructor would use the built-in arial-15 font.  Well, when I said built in, that file actually resides in gdx.jar which is included in your project.  A jar file is actually just a zip, so if you extract the file you can see all the code and assets that make up the gdx library itself.  Of particular interest to us is the folder \gdx\com\badlogic\gdx\utils, this is where the font file resides among other files:

 

image

 

Basically the GwtApplication is trying to access this file and doesn’t have permission to do so.  What’s the moral to the story?  Cross platform is awesome… but not always free!  Unless you need to support HTML, I would suggest not creating an HTML project, as it is by far the most fragile part of LibGDX and working with GWT causes all kinds of heartache and complication.  Your mileage may vary!

 

That said, there is a very simple fix to this, and it nicely illustrates how you deal with files between your projects… a process that may not be particularly intuitive.  The simple solution is to add the files arial-15.fnt and  arial-15 to the project and change the line:

font = new BitmapFont();

to

 

font = new BitmapFont(Gdx.files.internal("data/arial-15.fnt"),false);

 

This version of BitmapFont’s constructor takes a file handle of the font file you want the BitmapFont to use.  Gdx.files is used for file manipulation, internal returns a file handle to a file that is included within the project.  The false parameter is specifying that the font’s graphic isn't flipped upside down.

 

So, how do you actually add the file to the project?  You add them to the assets\data folder of the hello-world-android project:

image

 

You can add the files by simply dragging/dropping from Finder or Explorer to the data folder in the Package Explorer.

 

Now that the font file has been added, we can now run the HTML target:

image

 

So that’s Hello World in LibGDX.  Next up we look at something more advanced than Hello World.

Programming ,




GWT and Windows 8. GWT DMP Plugin has crashed possible fix

23. September 2013

 

I’ve recently been having a bit of a fight with Google development tools, GWT and the GWT plugin for Chrome on Windows 8 specifically.  Following the linked instructions I did manage to get the plugin installed, however today I started experiencing a new joy…  Every few minutes I would experience:

 

 

 

It would sometimes happen on load, other times when I tabbed back to Eclipse.  Apparently the GWT plugin is notoriously fragile.  Given the fact it doesn’t even run on Windows 8 without something of a song and dance, this isn’t really shocking.  I did however find a fix.  If you experience a GWT DMP Plugin crash in Chrome, check the following.

 

Go to chrome://extensions in Chrome.  Locate the plugin and click options:

image

 

In my case, there were no inclusions set for some reason.  Make sure localhost is added like so.  ( I did 127.0.0.1 too just in case… )

 

image

 

And, no more crashes!  That said, I’m still fed up with the entire process.  There is a project called Super Dev Mode that removes the plugin requirement completely, but there is an element of complexity involved. 

General ,




LibGDX Tutorial 1: Creating an initial project

19. September 2013

 

In case you’ve never heard of it, LibGDX is a Java based game library capable of targeting iOS, Android, Desktop ( Windows, Mac and Linux ) and HTML5.  It provides a full suite of 2D game functionality including Input, Graphics, Fonts,  Physics, Storage and increasingly, 3D.  So basically LibGDX is pretty much a one stop game libGDXdevelopment library.  This series is going to look at all of those aspects of LibGDX eventually.

 

EDIT: Jun 24/2014 

** IMPORTANT READ ME **

The process for creating a LibGDX project has changed substantially since this post was created.  There is now a Gradle based application that makes creating new projects much simpler and allows you to use IDEs other than Eclipse.

Read this post on getting started.  The portions of this post on running/debugging in Eclipse should still be valid.  For configuring IntelliJ IDEA to run LibGDX applications, refer to this post.

** END IMPORTANT READ ME **

 

 

The first part of getting started with LibGDX is installation.  If you haven’t got a Java/Android development environment set up yet, this portion is going to be a bit annoying.  In a nutshell you need to install in order the Java JDK, Android SDKEclipse, then Google ADT and finally the Google Plugin for Eclipse ( for GWT ).  I am not going into specifics about how to install all of these, however I went into pretty extreme detail in these instructions for setting up PlayN that cover most of the Eclipse related configuration.  If you run into a problem during the install, those instructions might help.  The process is actually pretty straight forward, it’s just long.  Oh yeah, one more thing you are going to need of course is LibGDX itself!  You can download it here.  In my limited experience, the nightly builds are actually pretty safe to use.  Common sense dictates you should use the stable version, but I am neither common nor sensible, so I’m going to risk it.

 

From this point on, I am going to assume you have a properly configured Eclipse install.  I am no huge fan of Eclipse and you have other options like NetBeans ( instructions ) or IntelliJ ( instructions ), but they are the less supported and slightly more complicated route.  Like it or not, if you are working with Android, Eclipse is still the path of least resistance.  Android Studio is a very encouraging option but sadly it’s Android focus make it a poor fit for LibGDX.

 

OK, let’s get started…

 

If you haven’t already, unzip the LibGDX archive somewhere.  I personally went with C:\dev\libgdx-0.9.8.  Keep the zip archive however.

Located and double click gdx-setup-ui.jar in the root directory of the libGDX.

The following Window should load:

image

 

If it doesn’t, you appear to have a problem with your Java install.

Click Create.

image

 

Fill in the resulting dialog.  You can see the values I used above.  You can optionally create a desktop, html and ios project.  The core and Android projects are mandatory.  Note, if you change the destination, you will have to specify the path to the LibGDX zip file.

 

Once you’ve specified the LibGDX path ( or if you didn’t change Destination ), the Generation button should be enabled:

image

 

Click it.

The following screen appears:

image

 

Click Launch.

All things according to plan, you should see:

image

 

If you don’t see the above messages, welcome to the LibGDX forums. Smile  StackOverflow is another good place for LibGDX related support as there are already 1,500 LibGDX tagged questions.

 

At this point we are done with the setup tool, you can close it.  If you navigate to folder you specified as the destination, you should see the following folder structure:

image

 

It should mirror the platforms you selected during setup.

 

Now it’s time to fire up Eclipse.

Now select File –> Import

image

 

Then select General->Existing Projects into Workspace and click Next.

image

 

Then the following dialog will appear:

image

 

With Select Root Directory checked, click Browse and navigate to the folder you chose as a destination earlier.  You should then see a list of available projects, all of which should be checked.  Then optionally choose if you want the project file copied within your Eclipse workspace.  When complete click Finish.

 

Now you should see:

image

 

hello-world ( or whatever you named the project ) is the common project, while each additional platform has a –platform suffix.

 

Running the desktop project

 

Let’s run the Desktop project now.

 

image

 

Right click helloworld-desktop, select Debug As->Java Application:

A dialog will appear and ask you what you want to run.  Locate your project main, then click OK.

image

 

Congratulations, your first ever LibGDX application!

image

 

 

Running the HTML project

 

Now try the same thing with the html5 appllication, right click, this time select Debug As->Web Application

image

 

A few seconds later you should see:

image

 

Double click the link and:

image

 

By the way, if you are running Chrome on WIndows 8, expect trouble.  This is why I hate working with Google tools…  anyways, the 5th suggestion in this post fixes the problem.  Or you could just use Firefox.

 

When working with HTML5 builds in Eclipse, there is something you should be aware of.  Running the web application again in the way listed above will fail.  It will try to start another web server and find the built in one already running and throw up.  You have two options, both in the Development Server window.

 

image

 

You can either use the red stop icon to shut down the internal web server, allowing you to run it using Debug As->Web Application.  Or you can hit the yellow arrows to reload your code.

 

Running an Android Project

 

When it comes to running an Android application, you’ve got a couple options.  First you can plug in an actual device.  If you use a device, make sure the ADB driver for it has been installed.  The ADB usb driver is part of the Android SDK.  This is by far the best way to work with Android.

 

If you don’t have a device, you can instead run the emulator.  If Eclipse doesn’t detect an attached device, it will try to launch the emulator.  If it cant find an emulator, it will fail.  Just a heads up, working with the emulator, especially for games, SUCKS.  Get a device, really, trust me on this one.

 

If you haven’t got a device and havent created an emulator yet, do so now.  You can do it from within Eclipse.  Select Window->Android Virtual Device Manager.

image

 

In the resulting dialog, click New:

image

 

Here is an example I’ve used.  Prefer emulating the Intel Atom chipset, it runs much faster.  If you are running an Intel chipset with HyperVisor support install the Intel Hardware Accelerated Execution Manager which can be downloaded here.  Or better yet, get a real device.  Did I mention that already?

 

image

 

The emulator is notoriously fragile, you will come to hate it quickly.  Did I mention you are better off getting a real device?

 

Now that your emulator is created, select it and click Start…

image

 

Go make some tea…

 

Drink your tea…

 

Perhaps a few crumpets?  A bagel perhaps?

 

Oh, hey, happy birthday!

 

Congratulations on your first born!!

 

Ok, it should be loaded now.  For the record… leave the emulator loaded.

 

Now you can run your Android application using Debug As or Run As->Android Application

image

 

And a few moments later, you should see:

image

 

Back in Eclipse, get to know and love LogCat.

image

 

It’s a great source of Android debug information.  This is where all trace, debug and error information is displayed.

 

So, what about iOS.  Well first off, I’m running on Windows right now, so there is no option.  Second, libGDX is currently in a bit of a transition state.  Previously it relied on MonoDevelop to deploy to iOS. Now it is transitioning to RoboVM for iOS support.  In the future I may specifically cover deploying to iOS… when I am on my Mac would be a good start!

 

In the next part we will look closer at project layout as well as get down to some coding.

Programming ,




Loom Engine has massive price drop and goes open source

19. September 2013

Although they didn't make an official blog post, nor have any information about it on their home page, there seem to have been some rather massive changes in the license structure for the Loom Game Engine.  I took a look at Loom several months back, it's an impressive 2D game engine using LoomScript ( an ActionScript/C# hybrid ) with a very Rails like workflow.  Previously it was 40$ a month, that seems to have changed:

LoomTurbo

 

From 40$ to 5$ a month is a rather spectacular change in price.  There is also now a free tier with the following restrictions.

No access to the following:

Easy Mobile Deploys
Command-Line Workflow
Live Reload
Dev Team Forum Support
Feature Request Voting


On top of that, they've announced they have gone open source on the Apache 2.0 license.

First, we have open sourced the Loom Native SDK! It is available under an Apache 2.0) license. The repository is available athttps://github.com/LoomSDK/LoomSDK. We are very excited to see you guys get directly involved in the development of Loom while we also offer more transparency about what we're working on. Not to mention that merging updates should be more convenient for you and - should you choose to do so - you also get to show off your involvement in an open-source project on your GitHub profile page!

 

The source code is available on Github. I'll admit, I'm a bit confused what exactly you get from the free tier, vs the Turbo tier vs just getting the source code.  TheEngine.co team are currently taking a vacation, so hopefully we will get a bit more clarification when they return.  In the meanwhile they have launched a new website, loomSDK.com.




Next project for GameFromScratch… a LibGDX tutorial series

17. September 2013

 

Now that the Blender series is finally complete ( phew, that sucker got long! ) it's onwards and upwards to a new project.  This will be a closer look at LibGDX, which I suppose will be a tutorial series of sorts.  I say of sorts because I really don't know enough about LibGDX to claim any kind of mastery.  In fact, I've barely even used Java in the last decade, so I've been recently polishing up my Java skills.

 

As a direct result, you aren't going to see best practices by any means.  Sometimes though, this is ideal, as I will have gone through exactly what you are about to go through if you are starting out learning LibGDX.  There are a number of tutorials out there on LibGDX right now but I see a common complaint or comment when it comes to LibGDX… "it's too complicated".  This isn't really fair, but I can completely understand where this perception comes from.

 

On the one hand, LibGDX is somewhat complicated simply based on what it does.  Supporting a number of platforms at once is bound to be complicated.  On top of that, it is built over tools that are exceedingly complicated ( I'm look at you Google! ).  Fortunately, the LibGDX team do a wonderful job of taking care of that stuff for you, so don't let that turn you off.  Another problem with LibGDX is, it provides multiple abstractions to work with.  This means you can work as high or low level as you want.  This is great but can make things a bit confusing.  Want a camera?  Great!  LibGDX has one.  Don't want to use it?  Great!  You don't have to!  This kind of stuff though isn't clear on first approach.

 

Another problem, and I am not sure if this is Java or Java programmers, but there is a tendency to engineer everything, some could say over-engineer everything.  Proper delegation of behaviour, good OO design, etc... When it comes to tutorials, especially beginner oriented tutorials, this is a mistake.  A tutorial should be as clear and concise as possible, even if it isn't pretty.  Having users dig across a dozen classes to grok a simple concept certainly isn't conducive to learning.

 

So, that is what I intend to accomplish.  To create a beginner friendly, thorough but comprehensive tutorial series covering LibGDX.  Just be aware up front, some of my code may be ugly and some of my LibGDX usage may be less than ideal.  I am not writing it to be pretty or fast, I am writing it to be clear.  At the end of the trip though, I hope what I create is truly useful and makes LibGDX a more approachable library for game developers out there, as it truly is a great one.

 

Oh, I am also working on a game project too, very possibly using LibGDX.  Hopefully I can share details of that project as it gets further along.

 

If there is anything specific in this series you want to see covered, let me know!