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Kivy Talk Python Meetup Innsbruck 2017.04.25

A talk about Kivy NUI framework held at Python Meetup in Innsbruck, 2017.04.25

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Kivy Talk Python Meetup Innsbruck 2017.04.25

  1. 1. KIVY NUI Applications with Python Python Meetup Innsbruck | 25. April 2017 Robert Niederreiter
  2. 2. CROSS PLATFORM kivy
  3. 3. ARCHITECTURE Widget Kv Language Cache Clock Gesture Event Loop Properties Core Providers Window Text Image Video Audio Graphics Vertex Buffer Frame Buffer Texture Shader Instructions Inputs Motion Event Post Processing (double tab, Dejitter, …) Pygame PIL Gstreamer FFMpeg SDL Cairo GLES API GLEW MouseTUIO WM_Touch Mac TouchMTDev HIDInput
  4. 4. App brought to foreground After process is killed (Android/iOS) Kivy bootstrap for Android/iOS Python start, run() build() on_start() Apps functionson_resume() Extenal App/OS or internal function pauses App on_pause() Save your work here. Resume is not guaranteed. on_stop() Kivy window destroyed Python stop on_pause() Resume? return True return False NoYes LIFECYCLE
  5. 5. EVENT LOOP Clock Events Loop Filesystem Network Process Other Motion Events Post Processing (double tab, swipe, ...) Input Processing Event Dispatcher Dispatch Input Events Custom Events Property Events Window Events GUI Touch Mouse Keyboard Joystick Other Input Kivy Main Thread Non GUI Operations (may run in dedicated thread) Main Loop
  6. 6. EventDispatcher App Widget Widgets are self-contained and organized as tree Animation Clock MotionEvent Layout Controls size and position of it's children FloatLayout BoxLayout GridLayout ButtonBehavior CoverBehavior DragBehavior behaviors ... Button Switch Slider Popup ... uix graphics Widget representation is done using canvas, graphics instructions are applied to it ContextInstruction VertexInstruction Color Rotate Scale ... Triangle Rectangle Ellipse ... Kv Language The KV language (sometimes called kvlang, or kivy language), allows you to create your widget tree in a declarative way and to bind widget properties to each other or to callbacks in a natural manner. ... OBJECTS Mixin Classes for Widgets
  7. 7. APPLICATION import kivy # replace with your current kivy version kivy.require('1.9.1') from import App from kivy.uix.label import Label class MyApp(App): # MyApp inherits from App object def build(self): # build returns the root widget return Label(text='Hello world') if __name__ == '__main__': MyApp().run()
  8. 8. REPETITIVE EVENTS from kivy.clock import Clock def my_callback(dt): # ``dt`` is delta time print('My callback is called'.format(dt)) # call ``my_callback`` X times per second event = Clock.schedule_interval(my_callback, 1 / 30.) # unscedule can be done by either using event.cancel() # or Clock.unschedule(event) def my_callback(dt): # if repetitive callback returns False, it gets unscheduled as well if some_condition: return False # regular processing Clock.schedule_interval(my_callback, 1 / 30.)
  9. 9. ONE-TIME EVENTS from kivy.clock import Clock def my_callback(dt): print('My callback is called'.format(dt)) # call ``my_callback`` once in one second Clock.schedule_once(my_callback, 1) The second argument is the amount of time to wait before calling the function, in seconds. However, you can achieve some other results with special values for the second argument: ● If X is greater than 0, the callback will be called in X seconds ● If X is 0, the callback will be called after the next frame ● If X is -1, the callback will be called before the next frame
  10. 10. INPUT AND PROPERTY EVENTS from kivy.uix.widget import Widget from import ListProperty class CustomBtn(Widget): # it's possible to bind to kivy property changes pressed = ListProperty([0, 0]) def on_touch_down(self, touch): # event handler for regular touch events if self.collide_point(*touch.pos): # setting pressed property triggers property event self.pressed = touch.pos # return True to indicate event consumed return True # delegate touch event to super class return super(CustomBtn, self).on_touch_down(touch) def on_pressed(self, instance, pos): # event handler triggered if ``pressed`` property changed print('pressed at {pos}'.format(pos=pos))
  11. 11. CUSTOM EVENTS from kivy.event import EventDispatcher class MyEventDispatcher(EventDispatcher): def __init__(self, **kw): # register custom event self.register_event_type('on_test') super(MyEventDispatcher, self).__init__(**kw) def do_something(self, value): # when do_something is called, the 'on_test' event will be # dispatched with the value self.dispatch('on_test', value) def on_test(self, *args): # default event handler print('I am dispatched'.format(args)) def my_callback(value, *args): print('Hello, I got an event!'.format(args)) ev = MyEventDispatcher() # instanciate ``MyEventDispatcher`` ev.bind(on_test=my_callback) # bind ``my_callback`` to ``on_test`` ev.do_something('test') # ``do_something`` dispatches ``on_test``
  12. 12. WIDGET TREE from kivy.uix.boxlayout import BoxLayout from kivy.uix.button import Button # create widget and add children layout = BoxLayout(padding=10) button = Button(text='My first button') layout.add_widget(button) # remove child from widget layout.remove_widget(button) # clear children layout.clear_widgets() # traversing the tree, iterate widget children for child in layout.children: print(child) # traversing the tree, access parent widget child = layout.children[0] Layout = child.parent # setting a z-index for a child widget layout.add_widget(widget, index)
  13. 13. KV LANGUAGE from kivy.uix.floatlayout import FloatLayout from kivy.lang import Builder Builder.load_string(''' <CustomLayout> Button: text: 'Hello World!!' size_hint: .5, .5 pos_hint: {'center_x': .5, 'center_y': .5} ''') class CustomLayout(FloatLayout): pass As your application grow more complex, it’s common that the construction of widget trees and explicit declaration of bindings, becomes verbose and hard to maintain. The KV Language is a attempt to overcome these short-comings. In the example above KV code is defined inside python module as docstring passed to Builder.load_string. KV code can also be contained in a separate file which can be loaded by using Builder.load_file('path/to/file.kv')
  14. 14. GRAPHICS class MyWidget(Widget): def __init__(self, **kw): super(MyWidget, self).__init__(**kw) with self.canvas: # add your instruction for main canvas here Color(1, 0, .4, mode='rgb') Line(points=(x1, y1, x2, y2, x3, y3)) with self.canvas.before: # you can use this to add instructions rendered before with self.canvas.after: # you can use this to add instructions rendered after MyWidget: canvas: Color: rgba: 1, .3, .8, .5 Line: points: zip(, Graphics instructions in Python Graphics instructions in KV language
  15. 15. Thank You! References: Credits: Photos by:

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  • hpeteragitator

    Apr. 26, 2017
  • jensens

    Apr. 26, 2017
  • andreapiovesana1

    May. 2, 2017

A talk about Kivy NUI framework held at Python Meetup in Innsbruck, 2017.04.25


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