Tutorial: Integrating Google Play Services with LibGDX

Source Code for tutorial on Github

Over the past week I have been working on adding online leader boards to my game FlyBy using the Google Play Services game API’s. As I ran into a few things that caught me out I thought I would write up how I got it working in hope it helps other people. So here we go:

Prerequisites

  • a Google developer account (this requires paying the $25 registration fee)

It is probably a good idea to have downloaded and got the Type-A-Number example from the Google developer site (which you can find here) working before you try integrating with LibGDX just to make sure you know how to handle the backend stuff on the website like setting up an OAuth 2.0 client ID and linking it to your app (which isn’t as hard as it may sound!). I’d highly recommend following that tutorial before this one. Some things to watch out for on Type-A-Number tutorial:

  • BaseGameUtils doesn’t import as a library, have to click the toggle box “isLibrary” on the projects properties (right click BaseGameUtils go to Properties>Android and tick the “isLibrary” box)
  • If you get “NoClassDefFoundErorr” when trying to run the project make sure to go the android projects properties > Java Build Path and make sure to tick the check box’s next to the dependencies your project uses.
  • Logging in with my developer account in game didn’t work for me, even with it set to be a tester (which happened automatically). If you are getting “Unknown Error” when attempting to sign in try using a different Gmail account (Be sure to add the account as a tester)

LibGDX Intergration

If you have got the Type-A-Number tutorial running your in a pretty good position, theres only a few changes needed to make it work with LibGDX. You can get the source code for this tutorial here. This tutorial assumes you are using Eclipse.

Step 1 - Import BaseGameUtils and google_play_services_lib into your LibGDX project.

  • The BaseGameUtils project is located from the Google Play Game Services Sample Games located here. It also came with the Type-A-Number tutorial so you can just grab it from there too.
  • google_play_services_lib is located in your android SDK folder at android-sdk\extras\google\google_play_services

To import the projects go to file>import>android>Existing Android Code into Workspace. Browse to the location of the lib your importing. The project should show up in the “Project to import” section. Make sure to click copy projects into workspace. Do this for both projects.

Step 2 - Add google_play_services_lib as a dependency for BaseGameUtils.

  • To do this right click BaseGameUtils and then click properties>Jave Build Path>Project>Add . In the popup box tick the google_player_services_lib and click ok. This should remove the errors BaseGameUtil was complaining about. If not try Project>Clean and hopefully that will help.

Step 3 - Add google_play_services_lib and BaseGameUtils as build dependencies for your Android project. To do this:

  • Make sure BaseGameUtils is set to “isLibrary” to do this right click BaseGameUtils go to Properties>Android and tick the “isLibrary” box.
  • Now add them to your Android project. Right click your Android project and go to Properties>Android in the library section click add and add both projects. They should appear in the pop up window after clicking add.
How it should look

How it should look

  • Right click your Android project and go to Properties>Java Build Path>Order and Export and make sure to tick the box next to ‘Android <your android version>’ and ‘Android Private Libraries’ as well as any others your project relies on (this is required for the newer Android Developer Tools).
How it should look

How it should look

At this point the game should compile and deploy to a device without any errors. We can now begin working on the code. We need need to set-up some interfaces for platform specific code. We will pretty much just be doing what is discussed on this page. But to begin with we will setup a xml file to hold some important values needed by Google Play Services.

Step 4 - Setup an xml file to hold values for the application id (that you get from your google developer page). The advantage of using an xml file like this means you don’t have to change the value throughout your project, just one place you put the value in and reference it from there everywhere else in your project

  • In your Android project go to res>values and create a new xml file (right click values folder> new> Android XML File and call it ids.xml then click finish. Either click the add button and create a new String. When the string is created name it  ’app_id’ and give it the value of your games ID from the Google developer page for your game or edit the file directory in the text editor by clicking the ‘ids.xml’ tab at the bottom.
  • Open your AndroidManifest.xml file and click the ‘AndroidManifest.xml’ tab at the bottom to get the text editor. We need to add some code to setup the ‘ids.xml’ to work so add the following code inside your ‘application’ tag. I have it under android:label

PasteBin Version of Code with better formatting

<meta-data android:name="com.google.android.gms.games.APP_ID"
            android:value="@string/app_id" />

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Step 5 – Create the base interface for platform specific code

  • Go to your main LibGDX project and create a new interface. I called it GoogleInterface. I set-up a very basic interface for this tutorial that has some very basic wrapping of some Google Play Services functions. You will most likely need to expand on this or create your own. But mine looks like the following:

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package com.me.gdxGooglePlay;

public interface GoogleInterface {

public void Login();
public void LogOut();

//get if client is signed in to Google+
public boolean getSignedIn();

//submit a score to a leaderboard
public void submitScore(int score);

//gets the scores and displays them threw googles default widget
public void getScores();

//gets the score and gives access to the raw score data
public void getScoresData();
}

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Step 6 - Create a class that implements the GoogleInterface for the Desktop implementation

  • Still in the main LibGDX project create a new class, I called it DesktopInterface and let it implement the GoogleInterface. My version of this class looks like the following:

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package com.me.gdxGooglePlay;

public class DesktopInterface implements GoogleInterface{

@Override
public void Login() {
System.out.println("Desktop: would of logged in here");
}

@Override
public void LogOut() {
System.out.println("Desktop: would of logged out here");
}

@Override
public boolean getSignedIn() {
System.out.println("Desktop: getSignIn()");
return false;
}

public void submitScore(int score){
System.out.println("Desktop: submitScore: " +score);
}

@Override
public void getScores() {
System.out.println("Desktop: getScores()");
}

@Override
public void getScoresData() {
System.out.println("Desktop: getScoresData()");
}
}

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Step 7 - In your projects main game class (the one that extends from ApplicationListener) create a constructor that takes an instance of GoogleInterface as a parameter. My constructor looks like this:

public Game(GoogleInterface aInterface){
platformInterface = aInterface;

platformInterface.Login();
}

As you can see I store the interface in this class, what you do with it once its in the project is up to you. I also call the interfaces Login method straight away so the game attemps to Login when it starts. In practice this probably isn’t a good idea. But for testing its fine.

Step 8 - Change MainActivity in your android project to implement GoogleInterface.

  • There is a lot going on at this stage. You need to make your MainActivity implement both GoogleInterface and GameHelperListener. This class will handle most of the actual talking with BaseGameUtils. I’ve set up a basic implementation that handles logging in, logging out, submitting and receiving scores. It probably isn’t suited to go straight into a game but demonstrates some ways to do these tasks. The main thing to note here is you pass the MainActivity into the Game constructor. Here is my class:

Pastebin version of code

If your getting an error with leaderBoardID you need to add it to your strings.xml file which is located in your Android project at res>values>strings.xml. The value for leaderBoardID should be the value of a leader board from your Google Developers page if you have made a leaderboard for the project.

At this point running the game should prompt you to choose a google account to log in with. If that actually happened, I’m surprised! If it didn’t, I probably forgot something or the tutorial needs to be more clear, so please contact me where you have got lost or what’s going wrong and I will try to help!

Source Code for tutorial on Github

LibGDX Mobile Game

So for the last few months I have been working on a small mobile game. I had to stop using Marmalade because I was unable to get a student licence and my trial expired. Because of this I have decided to moved back to LibGDX which actually supports iOS now. The process of getting a LibGDX game onto iOS seems a little daunting but I will give it a try anyways when the game is more complete. Anyways, here are some screen shots of what I’m working on:

Inside a cave

Inside a cave

Some spinning obstacles

Some spinning obstacles

A mine field

A mine field

The graphics are being created by Liam Bower. The game is basically a helicopter style game with extra features such as different areas, power ups and a shop. We hope to have it finished pretty soon, although it has already taken much longer than originally anticipated.

One interesting problem I had to work on recently was generating caves with smooth walls like in the first and second screen shot. Before smoothing the wall generation, the walls were generated in square blocks, and actually still are. What I do is convert the top and bottom blocks on the walls into two triangles.One triangle using the center point on the top edge of the block, the center point on the top edge of the next block, and its x and y position to draw a triangle. Then the other triangle just draws to fill in the rest of the block. This picture should help illustrate whats happening:

Debug drawing of triangles

Debug drawing of triangles

The results of this method are good, however it is probably more process intensive than it needs to be, and finding ways to optimize it will be something I will need to look into. One solution could be generating ‘height map’ like structures, and then using the triangles to draw from the edge of the screen to the tip point of the map. This will remove the drawing of all the boxes under the triangles as the triangles would create the entire terrain. Generating the terrain in wider sections will lower the number of triangles being drawn at once too.

The progress of the game is going good, with almost all the main features already programmed into the game, but there is still quite a lot of work to do before we can call it finished and release it…