It can be launched from the termux shell using the provided run_python.sh script, which can communicate with the Panda activity using a socket (which is the only way we can reliably get command-line output back to the program.)
The Python script needs to be readable by the Panda activity (which implies it needs to be in /sdcard).
The standard library is packed into the .apk, and loaded using zipimport. Extension modules are included using a special naming convention and import hook in order to comply with Android's strict demands on how libraries must be named to be included in an .apk.
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This can be done by setting the extra string org.panda3d.OUTPUT_URI to tcp://host:port
Writing to a log file can still be done using file:///path/to/log.txt
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It seems Android doesn't want an application to just quit on its own accord; after main() returns we need to kindly request Android to finish the activity and keep handling events until Android destroys the app.
The binary path we get from /proc/self/exe isn't very useful; the path to the .apk is barely more useful but it still doesn't make a whole lot of sense. It might make more sense to set it to the path of the native .so that is being loaded by NativeActivity.
These files are from the NDK, but don't seem to be included in termux. Since they are two small files that change very rarely, it's easier to just include them in the Panda repo.
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Sam Edwards
rdb
tobspr