Kivy: Drawing to widget - kivy

Question

I collect experiencies with kivy and I have problem with using widget center. My problem shows next script:
from kivy.uix.button import Button
from kivy.uix.widget import Widget
from kivy.uix.boxlayout import BoxLayout
from kivy.app import App
from functools import partial
from kivy.graphics import Color, Ellipse
class CanvasApp(App):
def draw(self,wid, color):
with wid.canvas:
Color(color[0], color[1], color[2])
Ellipse(size= (100, 100), pos=(wid.center_x, wid.center_y))
return
def painter(self, wid, *largs):
self.draw(wid, (0, 1, 0))
return
def build(self):
wid = Widget()
btn_painter = Button(text='Painter',
on_press=partial(self.painter, wid))
ctrl = BoxLayout(size_hint=(1, None), height=50)
ctrl.add_widget(btn_painter)
root = BoxLayout(orientation='vertical')
root.add_widget(wid)
root.add_widget(ctrl)
self.draw(wid, (1, 0, 0))
return root
if __name__ == '__main__':
CanvasApp().run()
I want to draw circle in the widget center (black rectangle) without using button painter. I don't able obtain actually center coordinates of center. Without using button are available only default center coordinates. How is OK process?
Thank you for answers.

Answer 1

The problem is that the wid size and position are not yet set inside the build() method. So you need to delay the call of draw() a bit. Try replacing the call to draw() with:
Clock.schedule_once(partial(self.draw, wid, (1,0,0)))
You will also need to change the draw() method slightly to handle the dt argument that gets added:
def draw(self,wid, color, *args):

Answer 2

I found solution of my problem. All explains follow script:
from kivy.app import App
from kivy.graphics import Color, Rectangle, Ellipse
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
class DrawArea(FloatLayout):
def __init__(self, **kwargs):
# make sure we aren't overriding any important functionality
super(DrawArea, self).__init__(**kwargs)
self.rect1 = None
self.li_item = []
return
def clear_area(self):
for item in self.li_item:
self.canvas.remove(item)
self.li_item.clear()
def draw_rect(self):
with self.canvas:
Color(0, 1, 0, 1) # green; colors range from 0-1 not 0-255
self.rect1 = Rectangle(size=self.size, pos=self.pos)
Color(1, 0, 0, 1) # green; colors range from 0-1 not 0-255
width = self.width/2
height = self.height/2
pos_x = self.center_x -width/2
pos_y = self.center_y - height/2
self.rect2 = Rectangle(size=(width, height), pos=(pos_x, pos_y))
self.li_item.append(self.rect1)
self.li_item.append(self.rect2)
return
def draw_circle(self):
Color(1, 0, 0)
d = 120
with self.canvas:
Color(0, 1, 0)
self.circle1 = Ellipse(size = (d,d), pos = (self.center_x-d/2, self.center_y-d/2))
Color(0, 0, 1)
self.circle2 = Ellipse(size = (d/2,d/2), pos = (self.center_x - self.size[0]/2, self.center_y - self.size[1]/2))
self.li_item.append(self.circle1)
self.li_item.append(self.circle2)
return
class MainApp(App):
def build(self):
self.task = 'circle'
root = BoxLayout(orientation = 'vertical')
self.dra = DrawArea()
button = Button(text = 'painter',size_hint=(1, None), height=50, on_press = self.but_paint)
root.add_widget(self.dra)
root.add_widget(button)
if self.task == 'circle':
self.dra.bind(pos = self._update_circ, size = self._update_circ)
self.dra.draw_circle()
else:
self.dra.bind(size=self._update_rect, pos=self._update_rect)
self.dra.draw_rect()
return root
def but_paint(self, instance):
#self.dra.clear_area()
if self.task == 'circle':
self.task = 'rectangle'
else:
self.task = 'circle'
if self.task == 'circle':
self.dra.bind(pos = self._update_circ, size = self._update_circ)
self.dra.draw_circle()
else:
self.dra.bind(size=self._update_rect, pos=self._update_rect)
self.dra.draw_rect()
return
def _update_circ(self, instance, value):
d = 120
pos1_x = instance.center[0] -d/2
pos1_y = instance.center[1] -d/2
self.dra.circle1.pos = (pos1_x, pos1_y)
pos2_x = instance.center[0] - instance.size[0]/2
pos2_y = instance.center[1] - instance.size[1]/2
self.dra.circle2.pos = (pos2_x, pos2_y)
return
def _update_rect(self, instance, value):
if self.dra.rect1 != None:
self.dra.rect1.pos = instance.pos
self.dra.rect1.size = instance.size
width = instance.size[0]/2
height = instance.size[1]/2
pos_x = instance.center[0] -width/2
pos_y = instance.center[1] - height/2
self.dra.rect2.pos = (pos_x, pos_y)
self.dra.rect2.size = (width, height)
def draw_rect(self):
with self.dra.canvas.before:
Color(0, 1, 0, 1) # green; colors range from 0-1 not 0-255
self.rect1 = Rectangle(size=self.dra.size, pos=self.dra.pos)
Color(1, 0, 0, 1) # green; colors range from 0-1 not 0-255
width = self.width/2
height = self.height/2
self.rect2 = Rectangle(size=(width, height), pos=(self.center_x -width/2, self.center_y - height/2))
return
if __name__ == '__main__':
MainApp().run()