Centering an object in Kivy

kivy, layout, python, user-interface

Solution

Snippet using `FloatLayout`, `size_hint` and `pos_hint`:

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

kv = '''
FloatLayout:
    Widget:
        size: min(root.size), min(root.size)
        size_hint: None, None
        pos_hint: {'center_x': .5, 'center_y': .5}
        canvas:
            Color:
                rgb: 1, 0, 0
            Ellipse:    
                size: self.size
                pos: self.pos
'''
Builder.load_string(kv)

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

MyApp().run()

Flag of Japan:

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

kv = '''
FloatLayout:
    canvas:
        Color:
            rgb: 1, 1, 1
        Rectangle:    
            size: self.size
            pos: self.pos   
    Widget:
        size: min(root.size)/2, min(root.size)/2
        size_hint: None, None
        pos_hint: {'center_x': .5, 'center_y': .5}
        canvas:
            Color:
                rgb: 1, 0, 0
            Ellipse:    
                size: self.size
                pos: self.pos
'''
Builder.load_string(kv)

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

MyApp().run()

Problem

I am trying to center a circle inside a layout. I'm currently doing some padding calculations, but I'm also looking for a better way. I imagine one of the predefined layouts may be a better choice. Here's what my code is producing... For square layouts: For wide layouts: This is the right behavior, which is great, but is there a better way? I can imagine this getting messy with non-circle shapes, for example. Here's my code: ``` #!/usr/bin/kivy import kivy kivy.require('1.7.2') from random import random from kivy.app import App from kivy.uix.widget import Widget from kivy.uix.gridlayout import GridLayout from kivy.uix.anchorlayout import AnchorLayout from kivy.uix.relativelayout import RelativeLayout from kivy.graphics import Color, Ellipse, Rectangle class MinimalApp(App): title = 'My App' def build(self): root = RootLayout() return(root) class RootLayout(AnchorLayout): pass class Circley(RelativeLayout): pass if __name__ == '__main__': MinimalApp().run() ``` And the KV: ``` #:kivy 1.7.2 #:import kivy kivy <RootLayout>: anchor_x: 'center' # I think this /is/ centered anchor_y: 'center' canvas.before: Color: rgba: 0.4, 0.4, 0.4, 1 Rectangle: pos: self.pos size: self.size Circley: anchor_x: 'center' # this is /not/ centered. anchor_y: 'center' canvas.before: Color: rgba: 0.94, 0.94, 0.94, 1 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) Label: text: unicode(self.size) # this is /not/ appearing color: 1,0,0,1 ```

Original source