Many OpenFrameworks Android apps are composed from a single activity, which derives from OFActivity and allow you to draw GL content in a canvas. This fits most cases. However, sometimes you need multiple activities, some with GL drawing and some without. OpenFrameworks Android supports such cases.

Add application initialization code

We can distinguish between application initialization and gl initialization. There are two methods in main.cpp, one for each. In most cases, there’s nothing to do in ‘ofAndroidApplicationInit’, and in ‘ofAndroidActivityInit’ we initialize the ofApp class.

‘ofAndroidApplicationInit’ allow you to do some initialization when the cpp side is created, even if the first activity is not a gl activity (for example, a completely native splash activity).

‘ofAndroidActivityInit’ is called when the gl canvas is initialized. This happens when the first OFActivity is created. Notice that if a second OFActivity is created on top of it, the canvas is recycled and this initialization code is not called again. However, if all OFActivites are destroyed, the canvas is indeed destroyed so when a new OFActivity is created, ‘ofAndroidActivityInit’ will be called again. The default implementation for this method instantiates the ofApp class, but you can add more code to it as needed.

Note that due to current architectural constraints, all activities share a single ofApp class and a single canvas. You cannot switch to different ofApp classes for drawing different activities as OpenFrameworks cannot currently hold multiple instances of the ofApp class in memory. It is up to you to signal the cpp side when a different activity is shown (when onResume is called on that activity), and perform different update/draw code to draw different content on the canvas.

Customizing the Android activity

OpenFrameworks supplies a base activity called OFActivity when the following conditions suits the project:

1) The first activity is this activity, meaning, the first activity in the application shows a gl canvas. 2) You want your activity to inherit from regular Android Activity class.

However, OpenFrameworks allows for more complicated scenarios, like having the first activity initializing the cpp side, but not the gl drawing (the first activity doesn’t draw gl at all, for example, a simple splash activity) or inheriting your activities from other classes, for example AppCompatActivity.

In order to achieve one or both the objectives above, you need to notify OpenFrameworks yourself on certain events, just like the original OFActivity does it:

In ANY activity in the application:

1) Whenever ANY activity is created OR resumed, you need to notify OpenFrameworks about it by calling OFAndroidLifeCycle.setActivity with this activity. 2) On the first activity created, you need to call OFAndroidLifeCycle.init() in order to initialize the cpp side. If this activity SHOULD NOT draw GL, you should call it with the parameter false in order to postpone canvas initialization.

In gl drawing activities:

1) in onCreate, call OFAndroidLifeCycle.glCreate() 2) in onResume, call OFAndroidLifeCycle.glResume() 3) in onPause, call OFAndroidLifeCycle.glPause() 4) in onDestroy, call OFAndroidLifeCycle.glDestroy()

You can look at the original OFActivity as a reference, and there’s also a detailed example with multiple activities in the android examples folder, called androidMultiOFActivityExample.

Tal Lavi & Artem Pyatishev.