Quick comparisons of solutions for 3D cross-platform (mobile) development

I spent some time lately comparing available development toolkits for 3D games / apps on mobile platforms (mostly for hobby / indy apps). I do not want to have to adapt to much my base code depending on the target platform, and was then looking at a toolkit to write most of the code once, and be able to build the app for various platforms on the market. My use case is: * sufficient 3D engine (not necessarily a high end thing, just the basics to be able to write 3D apps decently. I consider Three.js as sufficient for my needs for instance). * I am working on Linux, so the ability to dev on Linux would be a real plus. * of course, it should be as less expensive as possible :) * and finally, I am paying much attention at the EULA and licenses, as I do not want to force my users to send “anonymous” statistics, I do not want my app to need extra (and useless) permissions and so on.

Note: I did not test these toolkits deeply, and am just reporting here what I found while playing a bit with them and comparing the features, licenses and requirements. I only included

Cordova

First toolkit I had a look at was Cordova. It allows you to write pure web apps (using standard HTML / CSS / JS and providing some extra APIs to extend the available APIs, for bluetooth for instance) and to package them into native apps distributed through the market. What it does is basically add a wrapper around your web app to render it outside a browser, using the offered web abilities provided by webviews on iOs and on Android. Writing a web app is really super easy, and then having a first working prototype using Cordova is super fast. Cordova runs on Linux without any problems.

It works pretty well for 2D graphics and basic applications (but needs some extra permissions as it uses a web view, even if it is not communicating over internet). But when it comes to 3D graphics, using WebGL, you will be in troubles. Indeed, the webview in Android 4.x is using an old version of Chrome, even if you install the latest Chrome on your mobile. Then, you will not be able to use WebGL as it is simply not supported, unless you use some hack to actually use a more recent Chrome version, using Crosswalk for instance. On iOS, this is even worse as WebViews prior to iOS8 do not support WebGL (and as far as I know, there is no alternative which will be both stable, reliable and will go through the reviewing process of the appstore). This mean that you will not be able to target iPhones prior to (and including) iPhone 4, and iPad 1, which in my opinion is a real problem.

Unreal Engine

Second option is to use the Unreal Engine 4. It is a complete 3D game engine, including many tools to build 3D apps that you can deploy on many platforms (both desktop, web and mobile). You can code in C++ with it, and script using many visual tools. It includes dedicated APIs for advanced features such as Virtual Reality (VR) and may sound overkill.

You can dev using Windows and Mac (officially supported), but not Linux (at least, not officially). However, it seems that the dev editor can be installed on Linux at the cost of a bit of hacking, and this should be even easier to install in the near future as there seems to be a Linux community.

Unreal Engine charges you with 5% royalties passed the first 3k$.

Here are some relevant EULA fragments:

1. Hardware and Usage Data

You acknowledge that, as a default setting, the Engine Code will collect and send to Epic anonymous hardware and usage data from end users of Products. This functionality is used by Epic to improve the Engine Code. You may modify the Engine Code under the License to turn off that functionality in your Product, or you may include in your Product the capability for your end users to turn off that functionality in the Product.

and

You agree to keep accurate books and records related to your development, manufacture, Distribution, and sale of Products and related revenue. Epic may conduct reasonable audits of those books and records. Audits will be conducted during business hours on reasonable prior notice to you. Epic will bear the costs of audits unless the results show a shortfall in payments in excess of 5% during the period audited, in which case you will be responsible for the cost of the audit.

The second one is a standard one, as you have to pay royalties depending on your revenues. But the first one is really concerning, as by default Unreal Engine will track your users and send anonymous statistics (thus requiring extra and unneeded permissions and raising privacy concerns). However, once you are aware of it, you can freely modify your app to prevent this, according to the EULA, so this is not a big deal in the end.

Unity

Latest solution I found (used by Monument Valley for instance) is the Unity game engine. The personal license is sufficient in most of the cases, and is free to use up to 100k$ gross revenue. The dev tools are available on Windows and Mac, but there is no Linux version (and no hacky way to get it in Linux).

Here are some relevant fragments from EULA as well:

(c) users will be required to complete a user survey to activate the Software. Unity Pro users who are not eligible to use Unity Personal may not develop and publish Licensee Content for the iOS and Android platforms without purchasing the applicable Unity Pro Add-On Product license. Unity may monitor your compliance with and enforce these restrictions and requirements including but not limited to monitoring the number of downloads of your Licensee Content and any available revenue estimate data.

This one is not really clear, and I am not really sure of what it really implies. However, according to http://unity3d.com/legal/eula and https://unity3d.com/legal/privacy-policy, it seems to imply that statistics are sent and that you cannot avoid it, even in the pro version.

We also include certain device data collection in the runtime of the Software which is incorporated into the applications you create with the software. You should be sure that your privacy policy explains to your players the variety of technical information that is collected and shared with third parties like Unity.

and

Q: I play a game built with Unity software, what should I know?

A: Unity has probably collected some or all of the following information about your device: Unique device identifier generated from the device MAC/IMEI/MEID (which we immediately convert into a different number using a one way hash); IP address; Device manufacturer and model; the operating system and version running on your system or device; browser type; language; the make of the CPU, and number of CPUs present; the graphics card type and vendor name; graphics card driver name and version (example: “nv4disp.dll 6.10.93.71”); which graphics API is in use (example: “OpenGL 2.1” or “Direct3D 9.0c”); amount of system and video RAM present; current screen resolution; version of the Unity Player; version of the Unity Editor used to create the content; a number describing whether the player is running on Mac, Windows or other platforms; and a checksum of all the data that gets sent to verify that it did transmit correctly; application or bundle identification (“app id”) of the game installed. Some Unity developers use Unity’s analytics and ad services which collect additional information. See FAQs on Unity Analytics and Unity Ads below.

Q: That seems like a lot of data, why so much?

A: We try to limit the collection of this information from any one player or device; however, certain operating systems do not permit us to note that the info has already been collected. This means that the data may be sent to Unity each time you start the game. We use the information to make decisions about which platforms, operating systems and versions of them should be supported by our game development software. We aggregate this data and make it available to developers at stats.unity3d.com. This data helps us improve our Services and helps developers improve their apps.

1. Your choices about Unity’s collection and use of your information

   You always have the option to refrain from using the Service or to discontinue using the Service if you do not want information collected about you.

They also explictly says in the FAQ that there is no opt-out, and the anonymous stats are indeed browsable at http://stats.unity3d.com/mobile/. In conclusion, contrary to Unreal Engine, I do not think you can easily prevent the engine from sending anonymous statistics, which is a pity in my opinion. Moreover, there are a number of threads talking about extra permissions required by Unity (such as network access to send the statistics) and there seems to be no way to not require those permissions and to still conform to the EULA: http://answers.unity3d.com/questions/663197/how-to-prevent-unity-from-adding-permissions-to-an.html and http://forum.unity3d.com/threads/extra-permission-needed-in-android.295556.