Issues with Scatter size and position

Question

I encountered some issue related to scatter object. From my codes below. After I resize a Scatter (self.size_hint_x, self.size_hint_y = 0.3, 0.3), the objects (canvas, label) inside the Scatter is not resized as well. I did tried to apply size_hint=1 to the Canvas and Label inside the Scatter, however the result still the same.

Another issue I encountered is the retrieving of the X, Y position (relative to the parent) for the Canvas/Label in a Scatter. It always give me (0,0).

My Code

from kivy.app import App
from kivy.core.window import Window
from kivy.uix.widget import Widget
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.label import Label
from kivy.uix.scatter import Scatter
from kivy.graphics import Color, Rectangle, Canvas

class Avatar(Scatter):
    def __init__(self, **kwargs):
        super(Avatar, self).__init__(size_hint=(None,None), **kwargs)

        with self.canvas:
            Color(0, 0, 0)
            Rectangle(pos=(self.x, self.y), size=(self.width, self.height))

        self.lbl = Label(text='Test', size_hint_x=1, size_hint_y=1)
        self.add_widget(self.lbl)

        # Scatter size is 30% of the GameBackground
        # ISSUE: After resize my Scatter, the objects inside is not resized as well.
        self.size_hint_x, self.size_hint_y = 0.3, 0.3


class GameBackground(FloatLayout):
    def __init__(self, **kwargs):
        super(GameBackground, self).__init__(**kwargs)

        with self.canvas:
            Color(1, 0, 1)
            Rectangle(pos = (0, 0), size = (Window.width,Window.height))

        self.elf = Avatar()
        self.add_widget(self.elf)
        self.elf.x = 200
        self.elf.y = 300

        # Get the X, Y position of the Scatter and the label inside the Scatter relative to the parent.
        print self.elf.pos      #<-- This works.
        print self.elf.lbl.pos  #<-- ISSUE: This not working.


class GameApp(App):
    def build(self):
        return GameBackground()


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

Did I miss something? Thanks for any advise.

I'm new to Kivy. So pardon me if my qns is dumb. :P

Answer 1

Did you read the documentation for Scatter at all. It says that

...specific behavior makes the scatter unique, and there are some advantages / constraints that you should consider:

1. The children are positioned relative to 0, 0. The scatter position has no impact of the position of children.
2. This applies to the size too. If you want to resize the scatter, use scale, not size. (read #1.)

That answer your first question. It says use scale, not size. There is also the the method apply_transform that you may find useful for other transformations. I have never tried this method though but I cannot see the translate value (I can see Rotate and Scale)

Regarding to your second question. You are adding a Rectangle in the self.x and self.y position that is (0,0). So, your Rectangle is in that position. If you drag (using your fingers or mouse) your widget. The position of the Rectangle remains relative to the Scatter. So, unless you change the position of the Rectangle (with code) it will be always be in the (0,0). The transformations are always relative to the Scatter.

This question might be related and explains a few issues with not using the Kivy Language to add Vertex Instructions (i.e. Rectangles). You should consider it because what you are doing seems to be related.

* EDIT - just the necessarily corrections according to my understanding of what you are trying to achieve *

1) Don't use size hints like the ones you are using.

1.1) Instead of:

self.lbl = Label(text='Test', size_hint_x=1, size_hint_y=1)

use:

self.lbl = Label(text='Test', width=self.width, height=self.height)

1.2) And, instead of:

self.size_hint_x, self.size_hint_y = 0.3, 0.3

use:

self.scale = 0.3

2) The position is relative to the scatter. Therefore you need to transale the coordinates to the parent.

2.1) Instead of:

print self.elf.lbl.pos  #<-- ISSUE: This not working.

use:

print self.elf.to_parent(*self.elf.lbl.pos)

Here is the complete code:

from kivy.app import App
from kivy.core.window import Window
from kivy.uix.widget import Widget
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.label import Label
from kivy.uix.scatter import Scatter
from kivy.graphics import Color, Rectangle, Canvas

class Avatar(Scatter):
    def __init__(self, **kwargs):
        super(Avatar, self).__init__(size_hint=(None,None), **kwargs)

        with self.canvas:
            Color(0, 0, 0)
            Rectangle(pos=(self.x, self.y), size=(self.width, self.height))

        #self.lbl = Label(text='Test', size_hint_x=1, size_hint_y=1)
        self.lbl = Label(text='Test', width=self.width, height=self.height)
        self.add_widget(self.lbl)

        # Scatter size is 30% of the GameBackground
        # ISSUE: After resize my Scatter, the objects inside is not resized as well.
        # self.size_hint_x, self.size_hint_y = 0.3, 0.3
        self.scale = 0.3


class GameBackground(FloatLayout):
    def __init__(self, **kwargs):
        super(GameBackground, self).__init__(**kwargs)

        with self.canvas:
            Color(0, 0, 1)
            Rectangle(pos = (0, 0), size = (Window.width,Window.height))

        self.elf = Avatar()
        self.add_widget(self.elf)
        self.elf.x = 200
        self.elf.y = 300

        # Get the X, Y position of the Scatter and the label inside the Scatter relative to the parent.
        print self.elf.pos      #<-- This works.
        print self.elf.lbl.pos  #<-- ISSUE: This not working.
        print self.elf.to_parent(*self.elf.lbl.pos)

class GameApp(App):
    def build(self):
        return GameBackground()

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