Using Facebook SDK with Python-for-Android / Kivy

For another museum project, Arnaud asked me to see if we could integrate Facebook in an app on Android. The usual libraries are made for desktop, and manually open a webbrowser to handle the user authorization. But that’s not really nice for us, it would be nicer to have a native integration instead. Let’s see how we can use the official Facebook Android SDK.

Prerequisites

You’ll need to have:
– Kivy’s python-for-android
– A Facebook account (obviously)
Facebook SDK 3.0

Get the example

Clone the Kivy/Facebook example:

$ git clone https://github.com/tito/p4a-facebook-example

Register a Facebook application

  1. Go to the Facebook developers interface
  2. Click on Sélection_107
  3. Fill the information “App Name”. Don’t put “FB” or “Facebook” in the title, or your application name will be considered as Invalid :)
    Sélection_108
  4. Pass the captcha
  5. Write down your application id somewhereSélection_111
  6. Now, you need to activate Native Android App. The package name is the same name as the one we will pass in --package when building the APK. The Class Name is the packagename/activity. Activity class is always the same for all the applications compiled with python-for-android.
    Sélection_109
  7. Right now, the Facebook Android SDK will not authorize our android application to be used, because Facebook want to know the signature hash that will be used by our generated APK. To generate the key hashes, you need to use the keytool. Here is an example for the android “debug” key:
    $ keytool -exportcert -alias androiddebugkey \
       -keystore ~/.android/debug.keystore | \
       openssl sha1 -binary | openssl base64
    Enter keystore password:  android
    u+bzQmG87L298C4KGM8yODi3W/4=

    Copy the generated key hash, and paste it to the field:

    Sélection_110

Setup the our application

  1. Go into p4a-facebook-example, and edit the main.py
  2. Search for FACEBOOK_APP_ID, and replace with your own Application Id
  3. Go into python-for-android, and create a distribution:

    $ ./distribute.sh -m 'kivy'

  4. Go into the dist/default
  5. Generate the APK one time (for generating all the file we need to customize). Replace /path/to/p4a-facebook-example:

    ./build.py --name "Facebook test" --package org.test.facebook \
      --version 1 --private /path/to/p4a-facebook-example/ \
      --window --permission INTERNET debug

  6. Add a new reference to project.properties to include the Facebook SDK. The path to the Facebook SDK MUST be a relative path, otherwise you’ll get issues during the next build.

    android.library.reference.1=../../facebook-android-sdk-3.0.2/facebook

  7. Edit the templates/AndroidManifest.tmpl.xml to include the Facebook login activity, just under the <application>:

    <application android:label="@string/appName" android:icon="@drawable/icon">
    <activity android:name="com.facebook.LoginActivity"/>

  8. Rebuild your application… and you’re ready to test :)
  9. Install the application on your device:

    adb install -r bin/Facebooktest-1-debug.apk

Test your application

The Facebook SDK 3.0 require to separate read and publish permissions. To the user, it means you’ll have 2 dialog to accept. Even if you just want to publish to the application stream, you need to have the basic permission (read) accepted by the user before publish permissions. This is already implemented in the example app.

When you start the application the first time, you’ll have:

device-2013-08-08-110647

Depending if you have the Native Facebook application or not, you’ll have 2 kinds of authentification boxes.

Without Facebook installed on the device:
device-2013-08-08-110834

And with Facebook installed on the device:

device-2013-08-08-111002

After authentication, the user will need to accept our permissions:

device-2013-08-08-111111

It’s done!

The application have now the right to post :) The example post in the user stream as the application itself, not as the user. It’s called “publish_actions”.

Getting further

Obviously, when you use the Facebook SDK itself, you feel the pain of an API designed for Java. For every callback that Facebook want to call, you need to implement a Java class and define the callback method. Python is really simpler and fun to use.

See for yourself: we want to make a call of “Request.newStatusUpdateRequest“. Se weed first to implement a GraphUserCallback class, in Java. Thanks to Pyjnius, we can do it directly in Python:

class _FacebookGraphUserCallback(PythonJavaClass):

    __javainterfaces__ = ['com.facebook.Request$GraphUserCallback']
    __javacontext__ = 'app'

    def __init__(self, callback):
        self.callback = callback
        super(_FacebookGraphUserCallback, self).__init__()

    @java_method('(Lcom/facebook/model/GraphUser;Lcom/facebook/Response;)V')
    def onCompleted(self, user, response):
        self.callback(user, response)

This Python/Java class will call our own python callback when the Java callback onCompleted will be called. Then:

@run_on_ui_thread
    def post(self, text, callback):
        req = Request.newStatusUpdateRequest(
                self._session, text, _FacebookRequestCallback(callback))
        req.executeAsync()

All you have to do at the end, is to call the post method:

def fb_post(self, text):
        def callback(*args):
            from time import time
            self.post_status = 'message posted at {}'.format(time())
        self.facebook.post(text, callback=callback)

I don’t provide a wrapper around all the possible Request method you can do with Facebook. I just have an example for “post” and “me”. Both wrap “Request.newStatusUpdateRequest” and “Request.newMeRequest“. Please note that every request call must happen in the UI thread. Use the python-for-android/runnable module for that, with @run_on_ui_thread decorator.

The end

It was not easy to get it right, and it still complex to make all the pieces together. I’ve tried to use their own LoginButton (because they said that’s how they want it, everywhere), but i’ve not be able to use it in our app. Mostly because the LoginButton is a pure android widget, and because it doesn’t want to bring back the Activity after login. I was stuck too much time on it, and preferred to go in another way.
Please note that you should not share an application with a fake Facebook button, the design / look-and-feel must be the same as the original one.

I hope that will help some of you to get started !

GRDevDay 2013 and My Kivy Talk

I was lucky enough to give a talk about Kivy – a multi-touch, cross-platform Python GUI and application framework – at GRDevDay 2013. Although my talk was the least-attended talk I went to all day, I enjoyed giving it and I got to meet a few new Python folks from Michigan. I’m going to chalk up the attendance to the fact that I was in the same time slot as a lot of good talks, including three that I wanted to see myself. Ah well, such are conferences. At any rate, it gave me an opportunity to see what worked and what didn’t in this talk so I can make some changes before I give it at MobiDevDay Detroit in May.

Watching the

Watching the “So you think you know Javascript” talk at GRDevDay

GRDevDay was a great conference. The organizers really treat the speakers well with a semi-private speaker’s lounge and even special gifts. This is one of the few local events that I attend where I don’t do any organizing, and even though I feel like kind of a slacker, it also feels good to not have all of that pressure for the whole day. The GitHub-hosted drink-up at Kitchen76 was unbelievably crowded, but I still had fun and got to talk at length with some people I usually chat with infrequently online.

For those interested, I’ve posted the slides from my Kivy talk to Speaker Deck, and you can find the tutorial as it existed for the talk in this repository on GitHub.

[Edit 2013-03-05]
There were a few questions I was unable to answer at my GRdevDay talk. As I find answers, I will post them here.

Question: Can you make Android widgets using Kivy?
Answer: Probably not, but there has been a lot of work in pyjnius. No one has tried it recently.

[Edit 2013-03-07]
In my talk I said that you have to specify Android permissions in the Manifest.xml file. This is incorrect, you specify the permissions as part of the build command. See the Python for Android docs for more information.

Crowdfunding Kivy on Raspberry Pi

Kivy doesn’t run yet on the Raspberry Pi, and we need your help to crowdfund it!
Even is Kivy is built to be compatible for GLES 2.0, we lack of a python EGL support.

The plan is to add a new EGL Window provider, in addition to the detection of non-multitouch devices such as keyboard and mouse.

All the informations are available at: https://www.bountysource.com/#fundraisers/143-kivy-on-raspberry-pi

Pyjnius: Accessing Java classes from Python

We’re pleased to announce the Pyjnius project. It’s a Python library to access Java classes from Python, on the desktop or on Android.

We found others libraries such as JPype or Py4j, but we weren’t happy with the design and the usability. Using Jython wasn’t an option either, because we wanted to use the library within our python for android project.

Let me show you how simple it is to use Pyjnius:

>>> from jnius import autoclass
>>> Stack = autoclass('java.util.Stack')
>>> stack = Stack()
>>> stack.push('hello')
>>> stack.push('world')
>>> stack.pop()
'world'
>>> stack.pop()
'hello'

What we demonstrate here is the autoclass function that create kind-of proxy that reflect all the methods and fields available from the Java class java.util.Stack.

Ok, maybe you want an Android-related example? Just have a look:

from jnius import autoclass
from time import sleep

MediaRecorder = autoclass('android.media.MediaRecorder')
AudioSource = autoclass('android.media.MediaRecorder$AudioSource')
OutputFormat = autoclass('android.media.MediaRecorder$OutputFormat')
AudioEncoder = autoclass('android.media.MediaRecorder$AudioEncoder')

# Record the Microphone with a 3GP recorder
mRecorder = MediaRecorder()
mRecorder.setAudioSource(AudioSource.MIC)
mRecorder.setOutputFormat(OutputFormat.THREE_GPP)
mRecorder.setOutputFile('/sdcard/testrecorder.3gp')
mRecorder.setAudioEncoder(AudioEncoder.ARM_NB)
mRecorder.prepare()

# Record 5 seconds
mRecorder.start()
sleep(5)
mRecorder.stop()
mRecorder.release()

More examples are available in the documentation. We have a mapping between Java/Python type, native arrays, support for methods with multiple signatures, and a lot more. We are using Cython + JNI internally. The performance cost is minimal.

The library is already available for Python for android.

The library have been done by Gabriel Pettier and myself, under the Kivy organization.

IOS Support for Kivy

Kivy has now added official support for IOS platform. You can now package your Kivy application for the Ipad (and other iOS devices, testers needed).

The current instructions are available here: http://kivy.org/docs/guide/packaging-ios.html

For the full story on the multiple Apple limitations we are working with, i want to share the hardest part for Python integration: Apple’s prohibition on using dlopen() to load dynamic libraries.
In a typical case, a compiled Python library’s extension is a “.so”, and the “.so” is dlopen() at import.

That being said, as we did for the python-for-android project published in January, we are redirecting the compilation object to create static libraries. Theses libraries are included in the final application binary. But it’s not enough: we must also tell to Python to look for the library entry point in the application binary, instead of dlopen(). So in the python dynload loader:

return (dl_funcptr) dlsym(RTLD_MAIN_ONLY, funcname)

This way, Python will always look at the application binary, and never need to use dlopen().

If you are worried that Apple would reject a Python-based application, or even using Kivy altogether, we have tested it for you: the game that won the Kivy contest has been packaged for IOS, submitted to Apple… and accepted. You can found Deflectouch on iTunes (source code).

Anyway, Kivy is now officially supporting 5 platforms: Windows, Linux, MacOSX, Android and IOS!

Enjoy :)

Kivy programming contest #1 is over!

During January, we hosted a contest for promoting the Kivy framework. The goal was simple: create a game using Kivy, without external non-pure python dependencies. All the entries have been submitted on our sponsor Github (and thanks to NotionInk), under a compatible OSS licence. The contest registered 21 entries, and 11 submissions was valid.

Our winners are:

  1. Deflectouch, from Cyril Stoller
  2. FishLife, from Zogg
  3. memoryKivy, from Niavlys
  4. Centripetal, from Dilon Cower
  5. Flingy, from Andy Wilson

In term of numbers, everything is growing:

  • 19919 unique visitors for the website (vs 9772 in December)
  • +56 subscribers on the mailing list (192 in total)
  • 229 messages on kivy-users (vs 94 in December)
  • 23 pull requests (vs 6 in December)

That was a great event so far, with a perfect timing: Kivy have now 1 year old! (first release was 1st February 2011).

Introducing “Python for Android”

I’m glad to share a new project called Python for Android. The goal of this project is to package your python application into an APK.

https://github.com/kivy/python-for-android

The project is under the umbrella of Kivy organization, but is not designed to be limited to Kivy only. Read the documentation to correctly install the NDK/SDK Android, and set the needed environment variables.

The packaging is done in 4 steps:
1. Ensure you have Android SDK/NDK downloaded and correctly installed
2. Ensure you have some environment set
3. Create a Python distribution containing the selected modules
4. Use that distribution to build an APK of your Python application

Creating the python distribution is as simple as that:

# create a simple distribution with python + PIL + Kivy
./distribute.sh -m "pil kivy"

# create a distribution with python + openssl + pil + kivy
./distribute.sh -m "openssl pil kivy"

A directory dist/default will be created, including the result of the whole arm compilation.
Available libraries as for today: jpeg pil png sdl sqlite3 pygame kivy android libxml2 libxslt lxml ffmpeg openssl.

The second step is a little bit harder, since you need to provide more information for Android:

cd dist/default
./build.py --package org.test.touchtracer --name touchtracer \
--version 1.0 --dir ~/code/kivy/examples/demo/touchtracer debug installd

# --package: java name of your application
# --name: title of your application
# --version: version of your application
# --dir: location of your application containing the main.py

Then you’ll get a nicely bin/touchtracer-1.0-debug.apk

Pro:

  • A blacklist.txt file that can be used to exclude files in the final APK
  • Reusable distribution for other applications
  • Modular recipes architecture
  • Be able to build independents python distributions

Cons:

  • You need a main.py file that will be used for starting your application
  • Only one java bootstrap available, using OpenGL ES 2.0.
  • Only Kivy toolkit is working. I’m sure that other people can enhance it to add other toolkit recipes. But for example, pygame is not gonna to work because the android project is OpenGL ES 2.0: pygame drawing will not work.

I hope you’ll like it :)

We would like to thank Renpy / PGS4A for its initial pygame for android project

Kivy programming contest #1

Kivy, an open source project for building cross platform applications and user interfaces, is announcing its 1st programming contest. The contest will start with the publication of official rules on January 1st. Registrations will be accepted through January 25th, and submissions will be accepted through January 31st. Prizes include Nvidia Tegra 2 android tablets from NotionInk, One-year “bronze” plans and t-shirts.

The goal of the contest is to encourage interested developers to learn more about Kivy, which is a cross platform Application and User Interface software library for the python programming language. Kivy applications run on Linux, Windows, OSX, Android (and iOS). The framework supports most inputs protocols and devices like WM_Touch, WM_Pen, Mac OS X Trackpad and Magic Mouse, single/multi touch screens, Mtdev, Linux Kernel HID, TUIO, and uses pure hardware accelerated rendering to enable developers to really take user interfaces to a new level.

The contest is sponsored by NotionInk, an indian company that designs tablets PCs, and Github, a web-based hosting service for software developments projects.

Join the contest at : http://kivy.org/#contest

Kivy 1.0.8 released ! What’s next ?

101 days after 1.0.7, Kivy 1.0.8 have been released (changelog).

This release include:

  • New widgets: Virtual Keyboard, Accordion, ProgressBar
  • Video support on android – Python bindings for ffmpeg have been done and are available on github. Theses are focused to be usable on android within Kivy project, but any help to clean and make the code more crossplatform is welcome !
  • Scroll wheel support in scrollview
  • + 1.6x more performance on Kivy langage
  • Support for GIF image + set of images in Zip files
  • Bezier and stipple lines in graphics instructions
  • … and lot of improvements and fixes !

A documentation translation project have been started (thanks for Sphinx for generating gettext translations automatically from python autodoc). Help us at: http://translation.kivy.org/.

And now, where to go ?

The roadmap is not written, since what we do is mostly depending of our interests / jobs / contributions.
But community is growing fast ! I see $N multistroke recognizer, GSOC integration (better macosx integration), iOS port, better android packaging, unit test, better desktop integration, widget theming support, 3D graphics instructions…

If you still hesitating about using Kivy… just look at the frontpage for the current awesome projects made by the community. And they are lot of others projects going to be released during the next month ! We are also glad to see some big companies to use Kivy as the base for building their products.
If you have also cool project going on, don’t hesitate to share :)

To finish, here is a video from Cyril that playing on Icarus Touch, an instrument that use Kivy for his UI. Awesome work !

Texture compression, why does it matter ?

We all care about cash, time, life, love, and if you’re doing computer graphics, you might care about the memory consumption of your graphics card. Why ? For the same reason when you running out of cash :)

I’ll explain why does it matter to compress texture, and compare available possibilities. My personnal goal is to be able to load a lot of FULL HD pictures on tablet, for a museum project. The analysis is focused on DXT1 compression and size. I’m looking forward to ETC1 and will update that blog post with the result in the future.

What are we dealing with

If you are doing an application that display lot of hd pictures, that’s matter. We’ll start from this simple math statement: a full HD picture is 1980×1020 with 4 channels (RGBA). Whatever if your pictures is in PNG, or JPEG, your graphics card is not able to understand it, and will store it in its memory decompressed. So this image will eat:

1920 x 1080 x 4 = 8294400 bytes = 7.91MB
1920 x 1080 x 4 + mipmaps = 10769252 bytes = 10.27MB

In theory. Because it might be more if your graphics card doesn’t support NPOT texture. If not, usually, the texture will be resized to the closest POT texture available, mean for us: 2048 x 2048. Then the size for POT will be:

2048 x 2048 x 4 = 16777216 bytes = 16MB
2048 x 2048 x 4 + mipmaps = 22369620 bytes = 21MB

Compressions types

They are plenty types of compression availables. The most common are S3TC (including DXT1, DXT3, DXT5) from Savage3 originally, LATC from Nvidia, PVRTC from PowerVR, ETC1 from Ericsson…

Not all of them are available everywhere, and it’s depending a lot from your hardware. Here is a list of tablet / vendor / texture compression available. (only tablet, not desktop computer.) Thanks to this stackoverflow thread about supported OpenGL ES 2.0 extensions on Android devices

Tablette Vendor DXT1 S3TC LATC PVRTC ETC1 3DC ATC
(desktop computer) GeForce GTX 560 NVIDIA X X X
Motorola Xoom NVIDIA X X X X
Nexus One Qualcom X X X
Toshiba Folio NVIDIA X X X X
LGE Tablet NVIDIA X X X X
Galaxy Tab PowerVR X X
Acer Stream Qualcomm X X X
Desire Z Qualcomm X X X
Spica Samsumg X X
HTC Desire Qualcomm X X X
VegaTab NVIDIA X X X X
Nexus S PowerVR X X
HTC Desire HD Qualcomm X X X
HTC Legend Qualcomm X X X
Samsung Corby Qualcomm X X X
Droid 2 PowerVR X X
Galaxy S PowerVR X X
Milestone PowerVR X X

We are seeing that ETC1 is standard compression for OpenGL ES 2, unfortunately, it will not work on desktop.
PVRTC is specific to PowerVR device: it’s a standard on Ipad/Iphone.

Using DXT1

If you use DXT1, you need a POT image. DXT1 doesn’t work on NPOT.

To convert any image to DXT1 without any tool, you must know that your graphics card is capable of doing it, using specials opengl functions. But i wanted to precalculate them.
Nvidia texture tools contains tools for converting them, but you need an Nvidia card. For all others, you might want to look at Libsquish. It’s designed to compress in software a raw image to DXTn.
The result will be not a DXT1 “file”, because DXT1 is the compression format. The result will be stored in a DDS file, that we’ll see later about it.

If you want to be able to use libssquish in Python, you might want to apply my patch available on their issue tracker

For DXT1, the size of the file is not depending of the image content:

DXT1 2048x2048 RGBA = 2097152 bytes = 2MB

That’s already a big improvement. DXTn is able to store mipmaps of the texture too. For this size, the calculation is:

DXT1 2048x2048 RGBA + mipmap = 2795520 bytes = 2.73MB

Comparaison table

Type Resolution File size GPU size Images in a 256MB GPU Images in a 512MB GPU
Raw RGBA image (POT) 2048 x 2048 - 16384KB 16 32
PNG image (NPOT) 1920 x 1080 4373KB 8040KB 32 65
PNG Image in reduced POT resolution 1024 x 1024 1268KB 4096KB 64 128
DXT1 without mipmap 2048 x 2048 2048KB 2048KB 128 256
DXT1 without mipmap, reduced 1024 x 1024 512KB 512KB 512 1024
DXT1 with mipmap 2048 x 2048 2730KB 2730KB 96 192
DXT1 with mipmap, reduced 1024 x 1024 682KB 682KB 384 768

As soon as we use compression, what we see is:

  1. The file size is the same as GPU size
  2. Even with POT texture compared to NPOT dxt1, we can still store 4x more images in GPU

And with Kivy ?

DXT1 itself is the compression format, but you cannot actually use it like that. You need to store the result is a formatted file. DDS.

Kivy is already able to read DDS files. But you must ensure that your graphics card is supporting DXT1 or S3TC. Look at gl_has_capability() function in Kivy then.