You mean that the +/- buttons are used for volume control? Should be possible by setting a resource application class. Patches welcome.

try_init in apkenv means "try to see if you can handle this apk", which usually means looking if the library provides the necessary symbols. init is then called when the module has been chosen as the one to use (both are used in apkenv.c). While try_init does not get any additional parameters apart from the module itself (and should not do/allocate anything, as it will be called in all modules in order of priority until a working one is found), init already gets the screen size (width, height) and data directory where to store files.