105 lines
3.8 KiB
ReStructuredText
105 lines
3.8 KiB
ReStructuredText
Contribute
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Extending Python for android native support
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So, you want to get into python-for-android and extend what's available
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to Python on Android ?
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Turns out it's not very complicated, here is a little introduction on how to go
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about it. Without Pyjnius, the schema to access the Java API from Cython is::
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[1] Cython -> [2] C JNI -> [3] Java
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Think about acceleration sensors: you want to get the acceleration
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values in Python, but nothing is available natively. Lukcily you have
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a Java API for that : the Google API is available here
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http://developer.android.com/reference/android/hardware/Sensor.html
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You can't use it directly, you need to do your own API to use it in python,
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this is done in 3 steps
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Step 1: write the java code to create very simple functions to use
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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like : accelerometer Enable/Reading
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In our project, this is done in the Hardware.java:
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https://github.com/kivy/python-for-android/blob/master/src/src/org/renpy/android/Hardware.java
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you can see how it's implemented
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Step 2 : write a jni wrapper
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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This is a C file to be able to invoke/call Java functions from C, in our case,
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step 2 (and 3) are done in the android python module. The JNI part is done in
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the android_jni.c:
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https://github.com/kivy/python-for-android/blob/master/recipes/android/src/android_jni.c
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Step 3 : you have the java part, that you can call from the C
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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You can now do the Python extension around it, all the android python part is
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done in
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https://github.com/kivy/python-for-android/blob/master/recipes/android/src/android.pyx
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→ [python] android.accelerometer_reading ⇒ [C] android_accelerometer_reading
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⇒ [Java] Hardware.accelerometer_reading()
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The jni part is really a C api to call java methods. a little bit hard to get
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it with the syntax, but working with current example should be ok
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Example with bluetooth
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~~~~~~~~~~~~~~~~~~~~~~
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Start directly from a fork of https://github.com/kivy/python-for-android
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The first step is to identify where and how they are doing it in sl4a, it's
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really easy, because everything is already done as a client/server
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client/consumer approach, for bluetooth, they have a "Bluetooth facade" in
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java.
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http://code.google.com/p/android-scripting/source/browse/android/BluetoothFacade/src/com/googlecode/android_scripting/facade/BluetoothFacade.java
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You can learn from it, and see how is it's can be used as is, or if you can
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simplify / remove stuff you don't want.
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From this point, create a bluetooth file in
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python-for-android/tree/master/src/src/org/renpy/android in Java.
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Do a good API (enough simple to be able to write the jni in a very easy manner,
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like, don't pass any custom java object in argument).
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Then write the JNI, and then the python part.
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3 steps, once you get it, the real difficult part is to write the java part :)
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Jni gottchas
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~~~~~~~~~~~~
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- package must be org.renpy.android, don't change it.
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Create your own recipes
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-----------------------
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A recipe is a script that contains the "definition" of a module to compile.
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The directory layout of a recipe for a <modulename> is something like::
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python-for-android/recipes/<modulename>/recipe.sh
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python-for-android/recipes/<modulename>/patches/
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python-for-android/recipes/<modulename>/patches/fix-path.patch
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When building, all the recipe builds must go to::
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python-for-android/build/<modulename>/<archiveroot>
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For example, if you want to create a recipe for sdl, do::
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cd python-for-android/recipes
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mkdir sdl
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cp recipe.sh.tmpl sdl/recipe.sh
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sed -i 's#XXX#sdl#' sdl/recipe.sh
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Then, edit the sdl/recipe.sh to adjust other information (version, url) and
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complete the build function.
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