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Développeur Python et adepte Linux depuis 2005, Core développeur Kivy, passionné par beaucoup trop de choses.
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Entries tagged “kivy”

Building a background application on android with Kivy.

written by tshirtman, on 1/12/14 12:36 AM.

Kivy runs on android using the python-for-android project, which support android services. This works in a simple way, you basically bundle two main.py in your application, one for the UI, one for the service. The UI can start the services on start. From that point though, things may be a little uneasy. Why? Because you have two applications, and now you have to make them talk to each over if you want to do anything useful.

Android’s way of having an Activity and a Service talk to each other is Broadcast signals, which can be limited to part of your applications, howether, it’s not straightforward to use them with pyjnius, which is the magical interface we use to use java code from python.

Another way is to use network, i’ve been doing it with twisted in the past, setting a twisted server in the Service, and using twisted as a client in the Activity, howether, i find this to be heavy lifting for the trivial task of communicating between two programs on the same device. And including Twisted in your app, certainly add some weight to it.

Howether, in order to support TUIO, kivy ships with a simple OSC implementation, OSC is a simple connectionless network protocol, that allow you to pack messages, and send them to an ip/port/api URI, turns out we don’t need anything more, and a connectionless protocol avoid us dealing with disconnections (like the UI being closed, or the service not being started yet) that could give us some headaches (and certainly gave me some). We just need to have both part of the program listen for OSC messages, and have them send data to each other, if confirmation is needed, it’s possible to have a messages been sent back on a specific api.

So let’s get started.

getting a minimal kivy app

The usual things, let’s put a simple UI with a Button.

from kivy.app import App
from kivy.lang import Builder

kv = '''
Button:
    text: 'push me!'
'''

class ServiceApp(App):
    def build(self):
        return Builder.load_string(kv)

if __name__ == '__main__':
    ServiceApp().run()

here we just load a kv string that defines a button, and return the result, nothing fancy.

getting a minimal service

from time import sleep

if __name__ == '__main__':
    while True:
        sleep(.1)

Yeah, nothing much needed, actually, the sleep isn’t even needed, but the program have to run, and we’ll need this loop anyway.

starting the service

For your service to run, you need to tell your UI to start it.

from kivy.app import App
from kivy.lang import Builder
from kivy.utils import platform

kv = '''
Button:
    text: 'push me!'
'''

class ServiceApp(App):
    def build(self):
        if platform == 'android':
            from android import AndroidService
            service = AndroidService('my pong service', 'running')
            service.start('service started')
            self.service = service

        return Builder.load_string(kv)

if __name__ == '__main__':
    ServiceApp().run()

We make the test for android, so you can still test your app on desktop, by starting manually both parts.

Packaging them for android

both files must be named main.py, the UI one is at the root of the project, the other one is in a service directory directly under the root of the project.

├── main.py
└── service
    └── main.py

To package, i’ll be using buildozer.

As we are using network don’t forget to add the NETWORK permission when editing buildozer.spec

buildozer init
editor buildozer.spec
buildozer android debug deploy run logcat

After some time, you should see the (not very exciting) app start on your plugged android device.

setting up OSC

Whatever the side, OSC needs a port to listen on, and to have functions to call when things happen. The basic setup is simple.

from kivy.lib import osc

def some_api_callback(message, *args):
   print("got a message! %s" % message)

osc.init()
oscid = osc.listen(ipAddr='0.0.0.0', port=someport)
osc.bind(oscid, some_api_callback, '/some_api')

and then

osc.readQueue(oscid)

needs to be called regularly.

for the service, we’ll just put this call in the loop:

from time import sleep
from kivy.lib import osc

service = 3000

def some_api_callback(message, *args):
   print("got a message! %s" % message)

if __name__ == '__main__':
    osc.init()
    oscid = osc.listen(ipAddr='127.0.0.1', port=service)
    osc.bind(oscid, some_api_callback, '/some_api')

    while True:
        osc.readQueue(oscid)
        sleep(.1)

And for UI, we’ll use kivy.clock.Clock’s schedule_interval method.

from kivy.app import App
from kivy.lang import Builder
from kivy.lib import osc
from kivy.utils import platform
from kivy.clock import Clock

activityport = 3001

def some_api_callback(message, *args):
   print("got a message! %s" % message)

kv = '''
Button:
    text: 'push me!'
'''

class ServiceApp(App):
    def build(self):
        if platform == 'android':
            from android import AndroidService
            service = AndroidService('my pong service', 'running')
            service.start('service started')
            self.service = service

        osc.init()
        oscid = osc.listen(ipAddr='127.0.0.1', port=activityport)
        osc.bind(oscid, some_api_callback, '/some_api')
        Clock.schedule_interval(lambda *x: osc.readQueue(oscid), 0)

        return Builder.load_string(kv)

if __name__ == '__main__':
    ServiceApp().run()

Now, both sides can receive messages, that’s a good first step, but nothing will really happen, since none of them send any message.

sending messagse

The osc api to send message is very simple:

osc.sendMsg(api, data_list, port=someport, ipAddr=someaddress)

now, ipAddr is by default localhost, which is fine for us, so we only need to find the api we want to hit, the data list, and the port, which will be the one the other side listens on.

Let’s make our button send a message to the Service.

from kivy.app import App
from kivy.lang import Builder
from kivy.lib import osc
from kivy.clock import Clock

activityport = 3001
serviceport = 3000

def some_api_callback(message, *args):
   print("got a message! %s" % message)

kv = '''
Button:
    text: 'push me!'
    on_press: app.ping()
'''

class ServiceApp(App):
    def build(self):
        if platform == 'android':
            from android import AndroidService
            service = AndroidService('my pong service', 'running')
            service.start('service started')
            self.service = service

        osc.init()
        oscid = osc.listen(ipAddr='127.0.0.1', port=activityport)
        osc.bind(oscid, some_api_callback, '/some_api')
        Clock.schedule_interval(lambda *x: osc.readQueue(oscid), 0)

        return Builder.load_string(kv)

    def ping(self):
        osc.sendMsg('/some_api', ['ping', ], port=someotherport)


if __name__ == '__main__':
    ServiceApp().run()

Yes, at that point, you can run it, and see that when you press the button, your adb logcat on android, yay!

Now, let’s make our service answer, and our UI display the answer!

from time import sleep
from kivy.lib import osc

serviceport = 3000
activityport = 3001

def some_api_callback(message, *args):
    print("got a message! %s" % message)
    answer_message()

def answer_message():
    osc.sendMsg('/some_api', [asctime(localtime()), ], port=activityport)

if __name__ == '__main__':
    osc.init()
    oscid = osc.listen(ipAddr='127.0.0.1', port=serviceport)
    osc.bind(oscid, some_api_callback, '/some_api')

    while True:
        osc.readQueue(oscid)
        sleep(.1)

and for the UI to answer:

from kivy.app import App
from kivy.lang import Builder
from kivy.lib import osc
from kivy.utils import platform
from kivy.clock import Clock

activityport = 3001
serviceport = 3000

kv = '''
Button:
    text: 'push me!'
    on_press: app.ping()
'''

class ServiceApp(App):
    def build(self):
        if platform == 'android':
            from android import AndroidService
            service = AndroidService('my pong service', 'running')
            service.start('service started')
            self.service = service

        osc.init()
        oscid = osc.listen(ipAddr='127.0.0.1', port=activityport)
        osc.bind(oscid, some_api_callback, '/some_api')
        Clock.schedule_interval(lambda *x: osc.readQueue(oscid), 0)

        return Builder.load_string(kv)

    def ping(self):
        osc.sendMsg('/some_api', ['ping', ], port=someotherport)

    def some_api_callback(self, message, *args):
        print("got a message! %s" % message)
        self.root.text += '\n%s' % message[2]

if __name__ == '__main__':
    ServiceApp().run()

The only thing a bit confusing here is that the real message is in message[2], don’t ask me why, it’s probably explained in some documenation i didn’t care enough to search for :).

conclusion

That’s not much code! And it should be quite easy to extend to allow for more complex patterns, detecting if your service is running or not can be done by making it send pings at regular intervals, you can also make your service fetch/work on data from somewhere else in the background, and pass it to the UI when it’s ready.

A slightly more complex demo based on this can be found here.

Kivy hackathon in paris

written by tshirtman, on 4/16/13 12:04 AM.

Last week saw the first 24h hackathon event entirely dedicated to Kivy happening, in Paris. It was initiated by a hightly motivated student of the Cifacom school in paris, David Scheck, and attended by 4 groups of students, each with 3 to 5 members. I was pleased to share the hard task to help students discover the technology with my colleague Julien Miotte, from Majerti during the event.

The student weren’t very familiar with Python, and totally new to kivy, so it was a really challenging situation for both the student and the framework, would they be able to achieve anything in the hard limit of 24 hours?

First, after the students brainstormed on their project ideas, we got them through the major concepts and important classes of Kivy, using the Getting started page, it’s hard to get the point of properties accross in 10 minutes to student that didn’t have experienced the need of them, but I tried to at least make them aware it would be useful. The kv language presentation at this point, even if rudimentary, was probably useful, as we will see later.

Then students went on to try to build their project, except for a few quickly solved issues with windows installation, the starting was smooth. Julien and I gave some more explanations about how to start building a basic App (the doc is there, but who reads the doc? ;)) and people started designing their interface, and build the core of their application.

Eat Smart

One of the most required feature was certainly the use of multiple screens in an application, to build menu, so the use of ScreenManager was explained to at least two groups. Most of the end results consisted of interfaces done mainly in Kv, and some internal logic to display data, most group had a quite ambitious target, using geolocalisation, databases, complex interactions, and I wasn’t very optimistic on the odds of seeing them completed. Although I was right in that, I was still happy of the good designs they came up with, applications were incomplete (to a notable exception, will come back to that soon), but some interfaces were beautiful, reactive and engaging, so it was nice to see the magic happen in such a short time.

Floor2be

One group had a very different objective of the others, and although they had a difficult start, it turns out they were probably the best at teamwork, and had chosen a target they could actually achieve, a game! These motivated coders/artists came up with a classic 2D sidescroller, when the main character has to avoid elements on her way. Simple, to the point, and a quite a good realisation in such a short time, the fact that they created original artworks and integrated them in their game, and that the general theme had a nice touch of humour in the current political events in France certainly hearned them points, on top of having a completed project. They even could test it on Android during the competition time, and it was running perfectly. Their hard work earned them the right to run in a bigger international competition in the near future the angel hack in paris, next month, congratulation! I can only hope they’ll chose kivy as their secret weapon in this competion too.

The BoutinRun team at work

I would love to have better pictures, but i didn’t think much of taking them during the event, I should have better ones soon.

Debugging python-for-android with gdb

written by tshirtman, on 11/13/12 1:55 AM.

So i’ve been sinking a lot of time in trying to make python-for-android support multiprocessing, and for various reasons, it turns out to be a bad idea®, but in doing that, i had to go to great extents to understand more about python-for-android, about gdb, and about android itself. So, if it can save some trouble to others, i’ll try to document here the things i found how to do in this situation.

So the first thing to do is to get python-for-android compiled with debug symbols, so you can feed gdb with them, i found android-ndk-r8b to work much better after (well, to work at all), so it’s good to start with it, i put my changes in a branch of python-for-android repository, aptly called `debug` but they are not that big in fact, it’s mostly removing stripping in places, and adding -g in others.

With those changes, one can build a python-for-android distribution usable for debugging.

./distribute.sh -f -m 'kivy' -d debug

then, build your to-be-debugged application with this distribution, and install it, from then, you need a shell access to your android terminal (i use ssh, because adb over wifi is flacky but that’s another story, adb shell is good), you must then check if your terminal has the gdbserver command, if not, you can push it from the ndk to the terminal, and give it execution rights.

adb push ~/android-ndk-r8b/prebuilt/android-arm/gdbserver
adb shell
chmod 755 gdbserver

now, you can start your test program (from the UI), and tell gdbserver to attach to it,

ps | grep python
gdbserver :5050 --attach $pid

obviously using the pid found using the command, i use a shortcut though

./gdbserver :5050 --attach $(ps | grep python | tail -n 1 | tr -s " " " "| cut -d" " -f2)

This will tell gdbserver to listen on port 5050 (you can chose about any number between 1024 and 65536) and then the fun part begins

using the gdb in the ndk, load the pymodules.so file

$ ~/android-ndk-r8b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-gdb\
 ~/python-for-android/dist/debug/private/libpymodules.so

of course, this path (and the following ones) will need to be adapted to your system!

once in gdb, you’ll want to attach to the gdbserver on your device, i assume you are on the same wifi network as your device, but if not, you can do a port redirection through adb link i think

(gdb) target remote transformer:5050

If everything went fine, you should get a message a bit like this

Remote debugging using transformer:5051
warning: while parsing target library list (at line 2): No segment defined for com.showgen.processcraft.freemium:python
warning: Could not load shared library symbols for 87 libraries, e.g. /system/bin/linker.
Use the "info sharedlibrary" command to see the complete listing.
Do you need "set solib-search-path" or "set sysroot"?
warning: Unable to find dynamic linker breakpoint function.
GDB will be unable to debug shared library initializers
and track explicitly loaded dynamic code.
0x400b9384 in ?? ()

as the helpful message put it, we need to tell gdb where it can load the shared libs with debug symbols. Personnaly i found this setting of `solib-search-path`to work well:

(gdb) set solib-search-path \
/home/gabriel/python-for-android/src/obj/local/armeabi/:\
/home/gabriel/python-for-android/dist/debug/private/lib/python2.7/lib-dynload/:\
/home/gabriel/python-for-android/dist/debug/libs/armeabi/

You can check the result of this by using the command `info sharedlibrary` (or `i sh` for the lazy) to see if symbols have been found, the interresting part for me is:

0x56d31348  0x56d5c148  Yes         /home/gabriel/python-for-android/src/obj/local/armeabi/libsdl.so
0x579b5400  0x579d5798  Yes         /home/gabriel/python-for-android/src/obj/local/armeabi/libsdl_image.so
0x579fa428  0x57a2c1f8  Yes         /home/gabriel/python-for-android/src/obj/local/armeabi/libsdl_ttf.so
0x56a5a6b0  0x56a69c20  Yes         /home/gabriel/python-for-android/src/obj/local/armeabi/libsdl_mixer.so
0x5b985570  0x5bbc9e90  Yes         /home/gabriel/python-for-android/dist/billing/libs/armeabi/libpython2.7.so
0x56a79a1c  0x56a79c04  Yes         /home/gabriel/python-for-android/src/obj/local/armeabi/libapplication.so
0x56dee534  0x56dee5e8  Yes         /home/gabriel/python-for-android/src/obj/local/armeabi/libsdl_main.so
0x57604450  0x5761ed40  Yes         /home/gabriel/python-for-android/dist/billing/private/lib/python2.7/lib-dynload/_io.so
0x57a7426c  0x57a77630  Yes         /home/gabriel/python-for-android/dist/billing/private/lib/python2.7/lib-dynload/unicodedata.so
0x57b5b058  0x57b97d00  Yes         /home/gabriel/python-for-android/src/obj/local/armeabi/libsqlite3.so

Interrestingly, it seems the command is only useful after connecting to the target, doing it in reverse order doesn’t seem to bring any result, so the `search` is probably done only once, whet the search-patch is set.
Now, you can use the command `continue` or set breakpoints, or other rather common usage of gdb there. There are quite some resources out there about gdb usage :)

It’s not perfect, but i found it helping to be able to backtrace things on the tablet, in the nasty case you get a crash, or some weird “OSError”, with an unhelpful message, comming from the C side of things.

For the story, my error was likely caused by memory corruption due to the way we tried to reimplement the multiprocessing use of semaphore (sem_open being not implemented in android), and there is apparently no good way to do it. So i’ll look into android services instead when i have time, and try to give an API in python for that.

[Kivy] android-like pulldown menu

written by tshirtman, on 10/22/12 9:29 PM.

kivy all the things

As someone asked how to do such thing in kivy, i spent some time writting it, and as i (sadly) don’t blog on kivy often (if ever?), and since i think this example is quite telling about how kivy make such things quite easy, let’s talk a bit about this code.

To put things in context, what we want is the bar at the top of the android phones, that one can pull down to see notifications, this one is semi transparent and goes over the normal screen.

So, here is the code. first the kv part:

FloatLayout:
    FloatLayout:
        # placeholder for the "normal screen"
        Label:
            center: root.center
            text: 'test content'
            size_hint: None, None
            size: self.texture_size

    ScrollView:
        # container for the "notifications"
        y: dg.top # let's stick it to the top
        x: root.x # and to the left
        size_hint_y: None
        do_scroll_x: False # only vertical scrolling
        do_scroll_y: True
        
        # most of the magic is there, auto adjust size to follow the draggable label
        height: root.top - dg.y

        # let's put a nearly opaque black background
        canvas:
            Color:
                rgba: 0, 0, 0, .8
            Rectangle:
                pos: self.pos
                size: self.size
        
        # the actual notification container, with placeholder content
        BoxLayout:
            size_hint_y: None
            height: 1000
            orientation: 'vertical'
            Label:
                text: 'test'
            Label:
                text: 'test'
            Label:
                text: 'test'
            Label:
                text: 'test'
            Label:
                text: 'test'
            Label:
                text: 'test'
            Label:
                text: 'test'
            Label:
                text: 'test'
            Label:
                text: 'test'

    # the draggable label, which behaviour is defined in python file
    DraggableLabel:
        # some decoration behind the text
        canvas.before:
            Color:
                rgba: 0, 0, 0, 1
            Rectangle:
                pos: self.pos
                size: self.size
            Color:
                rgba: .5, .5, .5, 1
            Rectangle:
                pos: self.pos
                size: self.width, 1

        size_hint_y: None
        top: root.top
        # assign its id to "dg" so we can reference it elsewhere
        id: dg
        height: '20pt'
        text: 'drag me'

then the python part

from kivy.app import App 
from kivy.uix.label import Label
from kivy.animation import Animation


class DraggableLabel(Label):
    '''A label you can drag upside-down'''
    def on_touch_down(self, touch):
        if self.collide_point(*touch.pos):
            # assure ourselves we will get the updates of this motion
            touch.grab(self)
            return True

        return super(DraggableLabel, self).on_touch_down(touch)

    def on_touch_move(self, touch):
        if touch.grab_current is self:
            # really straightforward...
            self.y = touch.y
            return True

        return super(DraggableLabel, self).on_touch_move(touch)

    def on_touch_up(self, touch):
        if touch.grab_current is self:
            # check if the movement direction was up or down
            if touch.dy < 0:
                a = Animation(y=0) # down? put the bar all the way down
            else:
                a = Animation(top=self.parent.top) # up? put it at the top

            a.start(self) # actually start the animation
            return True

        return super(DraggableLabel, self).on_touch_up(touch)


class TabApp(App):
    pass


TabApp().run()

 

I think it doesn’t really need more explanations, the DraggableLabel is looking for touch events that are for it, first if they are on it, then if they are grabbed by itself, and move accordingly, and the kv auto adjust the size of the ScrollView to take all the distance between top of the screen and top of the DraggableLabel.

Of course, if things are not clear, feel free to ask questions :)

Tags

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