Python | Ellipse (different polygons) in Kivy

Kivy is a platform independent GUI tool in Python. As it can be run on Android, IOS, linux and Windows etc. It is basically used to develop the Android application, but it does not mean that it can not be used on Desktops applications.

Ellipse:

Ellipse is a vertex canvas instruction. It allows drawing of a regular polygon, or an arc based on them. In this article, we will see different polygons have different number of sides and also many vertices on circle.
As in Kivy, we can make polygons based on an ellipse. Note, the angles in Kivy, are different than those in math. In Kivy, the 0-degree point, corresponds to the 90 degree-point, in math.

Note:
These are the formulas for x and y. These math formulas assume the center is 0, 0. Thus, after calculations are done, there has to be a translation by x of a and y of b. The width is 2a, and height is 2b.



N segments = N vertices
1) angle[i]= i*360/n ; i=0 to n
2) x[i]=a cos(angle[i])
3) y[i]=b sin(angle[i])
4) In kivy 12’o clock is 0 degree and increases clockwise but in math 3’o clock is 0 degree increases counter clockwise.

Program to show how we can make different polygon in kivy by Ellipse.

main.py file:

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# Code to create different polygons using Ellipse
  
# import kivy module 
import kivy 
    
# this restrict the kivy version i.e 
# below this kivy version you cannot 
# use the app or software 
kivy.require("1.9.1"
    
# base Class of your App inherits from the App class. 
# app:always refers to the instance of your application 
from kivy.app import App 
  
# The GridLayout arranges children in a matrix. 
# It takes the available space and 
# divides it into columns and rows, 
# then adds widgets to the resulting “cells”.
from kivy.uix.gridlayout import GridLayout
  
# creating the Layout class 
class Ellipsekv(GridLayout):
    pass
  
# creating the App class    
class EllipseApp(App):
    def build(self):
        return Ellipsekv()
  
# run the App
if __name__=='__main__':
    EllipseApp().run()

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Ellipse.kv file

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# Ellipse.kv file of the code
  
###################################################
  
# For the arcs, we have to give the start,
# and the end angle. We use default number of segments,
# 180, and 5, for the two ellipse arcs.
# The rest of the kv file, corresponds, to the other,
# 6 ellipse arcs, following the same pattern.
  
#:set angle_start_row2 240 
#:set angle_end_row2 480
#:set angle_start_row3 120
#:set angle_end_row3 240
  
#################################################
  
  
<Ellipsekv>:
  
    # Setting coloumn to 4
    cols:4
  
##################################################
  
# Row 1
      
    # Creating Canvas
    canvas:
        Color:
            rgb: 0, 0, 1
        Rectangle:
            pos: self.pos
            size: self.size
  
    # This will create the circle
    # as no segement is fixed in Ellipse
    # so by default it creates the circle 
    RelativeLayout:
        canvas:
            Color:
                rgb: 1, .8, .5
            Ellipse:
                pos: 0, 0
                size: self.size
  
    # This will create pentagon as
    # segement = 5
    RelativeLayout:
        canvas:
            Ellipse:
                segments: 5
                pos: 0, 0
                size: self.size
  
    # This will create square shape as
    # segement = 4
    RelativeLayout:
        canvas:
            Ellipse:
                segments: 4
                pos: 0, 0
                size: self.size
  
    # This will create triangle as
    # segement = 3
    RelativeLayout:
        canvas:
            Ellipse:
                segments: 3
                pos: 0, 0
                size: self.size
                  
#################################################
  
# Row 2
  
    RelativeLayout:
        canvas:
            # Assigning colour to all in row 2
            Color:
                rgb: 1, .59, .86
  
            # Creating the arc as assigned above   
            Ellipse:
                angle_start: angle_start_row2
                angle_end: angle_end_row2
                pos: 0, 0
                size: self.size
  
  
    # Creating the arc as assigned above
    # segement 5
    RelativeLayout:
        canvas:
            Ellipse:
                angle_start: angle_start_row2
                angle_end: angle_end_row2
                segments: 5
                pos: 0, 0
                size: self.size
  
    # Creating the arc as assigned above
    # segement 4
    RelativeLayout:
        canvas:
            Ellipse:
                angle_start: angle_start_row2
                angle_end: angle_end_row2
                segments: 4
                pos: 0, 0
                size: self.size
  
    # Creating the arc as assigned above
    # segement 5
    RelativeLayout:
        canvas:
            Ellipse:
                angle_start: angle_start_row2
                angle_end: angle_end_row2
                segments: 3
                pos: 0, 0
                size: self.size
  
#################################################
  
# Row 3
  
    RelativeLayout:
        canvas:
            Color:
                rgb: .5, .5, .5
            Ellipse:
                angle_start: angle_start_row3
                angle_end: angle_end_row3
                pos: 0, 0
                size: self.size
  
    RelativeLayout:
        canvas:
            Ellipse:
                angle_start: angle_start_row3
                angle_end: angle_end_row3
                segments: 5
                pos: 0, 0
                size: self.size
  
    RelativeLayout:
        canvas:
            Ellipse:
                angle_start: angle_start_row3
                angle_end: angle_end_row3
                segments: 4
                pos: 0, 0
                size: self.size
  
    RelativeLayout:
        canvas:
            Ellipse:
                angle_start: angle_start_row3
                angle_end: angle_end_row3
                segments: 3
                pos: 0, 0
                size: self.size

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Output:

This is the result. We have 3 rows and 4 columns. Rows 2 and 3 are arc shapes, while Row1 has the default angles, 0 and 360 to form a complete circle. By changing the size of the window manually, we can get ovals, and shapes based on them. For the arc, the number of segments, corresponds to the number of lines that approximate the circular portion.



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