Rotating an object on a touch event in kivy

Question

I\'m working on making a circle that will spin kind of like a large dial. Currently, I have an arrow at the top to show which direction the dial is facing. I\'d like its b

Answer 1

You can bind angle of canvas to NumericProperty, to change it from inside your code. All you need to do is to compute those angles correctly. After playing a bit with it I created following code:

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.lang import Builder
from kivy.animation import Animation
from kivy.properties import NumericProperty

import math 

kv = '''
<Dial>:
    canvas:
        Rotate:
            angle: root.angle
            origin: self.center
        Color:
            rgb: 1, 0, 0
        Ellipse:    
            size: min(self.size), min(self.size)
            pos: 0.5*self.size[0] - 0.5*min(self.size), 0.5*self.size[1] - 0.5*min(self.size)
        Color:
            rgb: 0, 0, 0
        Ellipse:    
            size: 50, 50
            pos: 0.5*root.size[0]-25, 0.9*root.size[1]-25
'''
Builder.load_string(kv)

class Dial(Widget):
    angle = NumericProperty(0)

    def on_touch_down(self, touch):
        y = (touch.y - self.center[1])
        x = (touch.x - self.center[0])
        calc = math.degrees(math.atan2(y, x))
        self.prev_angle = calc if calc > 0 else 360+calc
        self.tmp = self.angle

    def on_touch_move(self, touch):
        y = (touch.y - self.center[1])
        x = (touch.x - self.center[0])
        calc = math.degrees(math.atan2(y, x))
        new_angle = calc if calc > 0 else 360+calc

        self.angle = self.tmp + (new_angle-self.prev_angle)%360

    def on_touch_up(self, touch):
        Animation(angle=0).start(self)

class DialApp(App):
    def build(self):
        return Dial()

if __name__ == "__main__":
    DialApp().run()

I'm calculating difference between initial (after pressing mouse) and later angle in on_touch_move. Since angle is a property I can also modify it using kivy.animation to make dial spin back after releasing mouse button.

EDIT

on_touch_down event for child circle:

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.uix.floatlayout import FloatLayout
from kivy.lang import Builder
from kivy.animation import Animation
from kivy.properties import NumericProperty

import math 

kv = '''
<Dial>:
    circle_id: circle_id
    size: root.size
    pos: 0, 0
    canvas:
        Rotate:
            angle: self.angle
            origin: self.center
        Color:
            rgb: 1, 0, 0
        Ellipse:    
            size: min(self.size), min(self.size)
            pos: 0.5*self.size[0] - 0.5*min(self.size), 0.5*self.size[1] - 0.5*min(self.size)
    Circle:
        id: circle_id   
        size_hint: 0, 0
        size: 50, 50
        pos: 0.5*root.size[0]-25, 0.9*root.size[1]-25
        canvas:
            Color:
                rgb: 0, 1, 0
            Ellipse:    
                size: 50, 50
                pos: self.pos              
'''
Builder.load_string(kv)

class Circle(Widget):
    def on_touch_down(self, touch):
        if self.collide_point(*touch.pos):
            print "small circle clicked"

class Dial(Widget):
    angle = NumericProperty(0)

    def on_touch_down(self, touch):
        if not self.circle_id.collide_point(*touch.pos):
            print "big circle clicked"

        y = (touch.y - self.center[1])
        x = (touch.x - self.center[0])
        calc = math.degrees(math.atan2(y, x))
        self.prev_angle = calc if calc > 0 else 360+calc
        self.tmp = self.angle

        return super(Dial, self).on_touch_down(touch) # dispatch touch event futher

    def on_touch_move(self, touch):
        y = (touch.y - self.center[1])
        x = (touch.x - self.center[0])
        calc = math.degrees(math.atan2(y, x))
        new_angle = calc if calc > 0 else 360+calc

        self.angle = self.tmp + (new_angle-self.prev_angle)%360

    def on_touch_up(self, touch):
        Animation(angle=0).start(self)


class DialApp(App):
    def build(self):
        return Dial()

if __name__ == "__main__":
    DialApp().run()

Answer 2

You can use GearTick from garden which is a rotating slider. It's not exactly what you need but can be adapted for your needs. "By default it allows rotation anti-clockwise you probably would need it to go clockwise"(Update: The widget now has a orientation property that can be set to 'clockwise' or 'anti-clockwise').

You would need to manage the spring back and stopping at the "finger stop".

The example at the ends manage spring back using animation, however you still need to manage/implement the finger stop functionality.

https://github.com/kivy-garden/garden.geartick

Usage::

Python::

from kivy.garden.geartick import GearTick
parent.add_widget(GearTick(range=(0, 100)))

kv::

BoxLayout:
    orientation: 'vertical'
    GearTick:
        id: gear_tick
        zoom_factor: 1.1
        # uncomment the following to use non default values
        #max: 100
        #background_image: 'background.png'
        #overlay_image: 'gear.png'
        #orientation: 'anti-clockwise'
        on_release:
            Animation.stop_all(self)
            Animation(value=0).start(self)
    Label:
        size_hint: 1, None
        height: '22dp'
        color: 0, 1, 0, 1
        text: ('value: {}').format(gear_tick.value)

To install::

pip install kivy-garden
garden install geartick

Working Example that you can copy paste::

from kivy.lang import Builder
from kivy.app import runTouchApp
from kivy.garden.geartick import GearTick
runTouchApp(Builder.load_string('''
#:import Animation kivy.animation.Animation
GridLayout:
    cols: 2
    canvas.before:
        Color:
            rgba: 1, 1, 1, 1
        Rectangle:
            size: self.size
            pos: self.pos
    BoxLayout:
        orientation: 'vertical'
        GearTick:
            id: gear_tick
            zoom_factor: 1.1
            # uncomment the following to use non default values
            #max: 100
            #background_image: 'background.png'
            #overlay_image: 'gear.png'
            #orientation: 'anti-clockwise'
            on_release:
                Animation.stop_all(self)
                Animation(value=0).start(self)
        Label:
            size_hint: 1, None
            height: '22dp'
            color: 0, 1, 0, 1
            text: ('value: {}').format(gear_tick.value)
'''))