

Virtual reality is starting to take off, and not to be left behind, Google released the Google VR SDK and NDK. With this, Google plans on bringing virtual reality to the mobile masses by allowing developers to easily implement VR apps. With the recent Daydream announcement, the Google VR SDK has been updated with full Daydream support. While VR support for both desktops and mobile are supported in engines like Unity, we will just be focusing on Android Studio development here. Let’s get started.

What do the Google VR SDK and NDK offer?



Virtual reality is defined as a computer generated 3D world in which the user can interact with by a headset, like Google Daydream, the HTC Vive, or the Oculus Rift, or by other means such as gloves and other various sensors. Mostly focusing on the headset at the moment, the VR SDK enables a way for developers to harness the power of a device to be used as the screen to view the 3D world along with the ability to use other peripherals depending on what the developer wants. The Google VR NDK allows for native development just like the regular Android NDK, but this time for VR.

Getting everything set up



Getting everything up and running is actually pretty easy. Make sure you have the latest Android N preview SDK installed along with the latest build-tools and platform-tools as well as the JDK 1.8. Then, download the samples here and that’s it! Everything should be ready to go. To open in Android Studio, open the main folder “gvr-android-sdk-master” to include all of the samples. Keep in mind that Android Studio may not recognize all of the modules right away, just give it a minute and everything will act like normal. In the next section we will dive deeper into the sample app “Treasure Hunt”. A quick note: While the Android NDK is not technically required for this, it may be a good idea to install it. A guide to do that can be found here.

Testing the Treasure Hunt sample app

This is one of the cooler sample applications included with the VR SDK. This is a very simple game in which you look around and find the rotating cube then press a button to interact with it. To run this, just simply select the “samples-sdk-treasurehunt” module in Android Studio and press the play button. Make sure you have a compatible Android phone (Android 4.4 KitKat or higher) connected to your computer and have a VR headset like Google Cardboard.

Understanding the code to make VR work



Since virtual reality happens in a 3D space, OpenGL is the obvious API of choice for this, at least until Vulkan hits the Android mainstream. Noting this, a basic understanding of 3D space is required. You need to know is that there are 3 axes: X, Y and Z in which the world is rendered in. This is important to note as the code references these quite a bit. Also note that “yaw” and “pitch” are X axis movement and Y axis movement respectively. Let’s first take a look at the Android Manifest for Treasure Hunt:

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.google.vr.sdk.samples.treasurehunt" android:versionCode="1" android:versionName="1"> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.NFC" /> <uses-permission android:name="android.permission.VIBRATE" /> <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /> <!-- Make accelerometer and gyroscope hard requirements for good head tracking. --> <uses-feature android:name="android.hardware.sensor.accelerometer" android:required="true"/> <uses-feature android:name="android.hardware.sensor.gyroscope" android:required="true"/> <uses-sdk android:minSdkVersion="19" android:targetSdkVersion="22"/> <uses-feature android:glEsVersion="0x00020000" android:required="true" /> <!-- VR feature tags. --> <uses-feature android:name="android.software.vr.mode" android:required="false"/> <uses-feature android:name="android.hardware.vr.high_performance" android:required="false"/> <application android:allowBackup="true" android:supportsRtl="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name"> <activity android:name=".TreasureHuntActivity" android:label="@string/app_name" android:screenOrientation="landscape" android:configChanges="orientation|keyboardHidden|screenSize" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> <category android:name="com.google.intent.category.CARDBOARD" /> </intent-filter> </activity> </application> </manifest>

Starting from the top, the permissions needed are as follows: NFC, External storage reading and vibration. The minimum SDK version needs to be 19, or KitKat for VR to work. The next line may be new to you, but this is where the minimum OpenGL version is defined. Devices that don’t supports OpenGL 2.0 or high can’t run VR apps. Moving down to the intent-filter, the main thing to note is “com.google.intent.category.CARDBOARD” which will enable the ability for the app to be visible in Google’s Cardboard app as a compatible Cardboard app.

GvrActivity – This is the starting point for making a VR app with the Google VR SDK. Notice that the TreasureHuntActivity extends GvrActivity in the app code. This activity handles most of what is needed to interact with VR devices and to get everything working. It is good to note that this activity uses “sticky immersive mode”, which hides the system UI and makes the app full screen, this activity only works in this mode, so don’t change this attribute!

GvrView – Everything that has to do with the user interface is rendered in a view in Android, and VR is no different. GvfView renders the scene in stereo, meaning there are two separate scenes rendered on the screen, one for each eye. Here is a snippet from the activity layout XML (common_ui in the sample app) in the res-layout folder. You would need to add this yourself if you were starting from scratch:

<com.google.vr.sdk.base.GvrView android:id="@+id/gvr_view" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_alignParentTop="true" android:layout_alignParentLeft="true" />

This gets everything ready to go for the layout. Next up is the main activity code that goes in the OnCreate() method:

** * Sets the view to our GvrView and initializes the transformation matrices * we will use to render our scene. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.common_ui); GvrView gvrView = (GvrView) findViewById(R.id.gvr_view); // Associate a GvrView.StereoRenderer with gvrView. gvrView.setRenderer(this); // Associate the gvrView with this activity. setGvrView(gvrView); // Initialize other objects here. ... }

Now that GvrView is set up, we can dive into the GvrView.StereoRenderer which includes two methods: onNewFrame(), which is called everytime the app renders and onDrawEye(), which is called for each eye with different eye parameters. Examples of these can be found in Google’s Understanding the Treasure Hunt sample game documentation.

Spatial Audio – This is a 3D audio that makes it seem like you are hearing something at any point in 3D space through standard stereo means, this can be defined in the OnCreate as:

gvrAudioEngine = new GvrAudioEngine(this, GvrAudioEngine.RenderingMode.BINAURAL_HIGH_QUALITY);

Inputs – There is also the ability to handle inputs from the user, like the button on most Google Cardboard devices. This can be achieved in the onCardboardTrigger() method in the main activity of your app, a simple example is:

/** * Called when the Cardboard trigger is pulled. */ @Override public void onCardboardTrigger() { if (isLookingAtObject()) { hideObject(); } // Always give user feedback mVibrator.vibrate(50); }

This checks to see if the user is looking at the cube and to hide the cube if they are and press the button, as well as vibrate the device.

The TreasureHunt sample goes a lot more in depth than just the basics, including rendering the cubes, which is done in the “WorldLayoutData” file. Here the coordinates and colors are defined in floating point values. There are also the implementation of OpenGL shaders as .shader files. These shaders mainly deal with what type of light is reflected off of the material of the cubes and the like. For more information then check out the official documentation for OpenGL shaders. Everything else is in standard Android fashion, so if you have experience with normal Android development, it will be easy to grasp the rest of the files included in the sample.

Wrap Up

Developing for virtual reality is a little different from regular Android development, with the only real learning curve being OpenGL development and possibly native development if you go down that road. It is probably a good idea to start out with regular Android development or to use an engine if you are just starting out. The good news is it isn’t as hard as you think, to get started with 3D game development then read our how to write a 3D game for Android using Unreal Engine guide, or maybe check out our how to create your first Gear VR app tutorial.

Are you interested in VR or even making apps for VR? Let us know in the comments below! Also, be sure to stay tuned to VR Source for everything VR!