The aim of the project was to learn how to build an Android application of some complexity with features like OpenGL rendering, integration with backend server, Google AdMob for serving ads, Google Analytics tracking of application usage, SD storage and possibility to run on both phones and tablets with appealing layout and performance.
Lesson learned 1 - 3D
Accelerated 3D graphics is hard even if you're experienced with desktop OpenGL. To make OpenGL ES work on all devices requires a lot of testing which you can't do without devices. And generally debugging accelerated graphics in the Android emulator is no fun. Therefore, use a library to leverage yourself from the low level details.
I looked into jMonkeyEngine, libgdx which are general and large frameworks with quite massive APIs which probably would have worked out great but seemed to have some threshold for a newcomer to overcome.In the end I decided to work with the more limited jPCT which has worked out very well. A stable and reliable library with an active community. jPCT handles 3DS-models well which makes it easy to create environments via some tooling.
I used the open source modeller Blender which is free and has support for all you would need as sculpt modelling and texture UV coordinate tooling. Antother appealing feature of jPCT is that is developed both for Android and as standard Java for desktop so you can port your apps between them without great effort.
Lesson 2 - Revenue model
If you haven't decided whether charging for your app or using ads I can only say that Ads are easy! If you're familiar with Google AdSense for creating ads on your websites you'll find it intuitive to work with Google AdMob. If you have an Android Activity made up of standard Android layouts you can simply add an AdView view to your layout and the Ad library will populate the container with ads.
Compared to the standard Google AdSense interfaces for managing and following up your ad reports AdMob is more limited and not as well polished but who cares? Will revenues be larger with mobile app ads than with ordinary web ads? I'll come back later on that.
Lesson 3 - Mobile is not desktop
Memory is scarse when you go down the 3D pathway. I early discovered that you must be cheap on your textures and the polygon levels of your meshes. The devices have no problem with rendering polygon heavy meshes with impressive framerates, but you soon run out of memory if you don't do clever texture unloads when you don't need them. My lesson here was: Create a game engine with strict modules for each game state so that you can be sure to deallocate all resources when you change state and use more low res textures than you usually would.
Lesson 4 - Tune your app after how your users use it
So in this game each level becomes more difficult and it seems like a good tuning approach to make the difficulties of the first two levels easy enough to to make sure all players passes them. After that it should be exponentially more difficult. How to know how your app users are doing? I notices that the game was way too hard when I tried it on people. Some sort of surveillance would be nice without intruding in the users' privacy. Lesson here is to not invent anything new. By using Google Analytics you can track how users travel around in your application by marking different states as you would use Google Analytics to mark web pages in a web site to follow traffic around your site and adapt your game to how users respond.
Lesson 5 - Android is not Java
Another more depressive lesson learned is that when you plan to reuse some Java library first make a Google search whether anyone has had difficulties using it on the Android platform. For example the JSON marshaller Jackson proved to be hard to use.
