Python| Kivy中的椭圆（不同的多边形）

Kivy 是Python中一个独立于平台的 GUI 工具。因为它可以在Android、IOS、linux和Windows等平台上运行。它基本上是用来开发Android应用程序的，但这并不意味着它不能在Desktops应用程序上使用。

Kivy Tutorial – Learn Kivy with Examples.

椭圆：

Ellipse 是一个顶点画布指令。它允许绘制正多边形或基于它们的弧。在这篇文章中，我们将看到不同的多边形有不同的边数以及圆上的许多顶点。
就像在 Kivy 中一样，我们可以基于椭圆制作多边形。请注意，Kivy 中的角度与数学中的角度不同。在 Kivy 中，0 度点对应于数学中的 90 度点。

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. 

程序展示了我们如何通过 Ellipse 在 kivy 中制作不同的多边形。

main.py 文件：

Python3

# 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()

椭圆.kv 文件

Python3

# 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
 
#################################################
 
 
:
 
    # Setting column 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 segment 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
    # segment = 5
    RelativeLayout:
        canvas:
            Ellipse:
                segments: 5
                pos: 0, 0
                size: self.size
 
    # This will create square shape as
    # segment = 4
    RelativeLayout:
        canvas:
            Ellipse:
                segments: 4
                pos: 0, 0
                size: self.size
 
    # This will create triangle as
    # segment = 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
    # segment 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
    # segment 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
    # segment 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

输出：

这就是结果。我们有 3 行和 4 列。第 2 行和第 3 行是弧形，而第 1 行具有默认角度，0 和 360 度以形成一个完整的圆。通过手动改变窗口的大小，我们可以得到椭圆，以及基于它们的形状。对于圆弧，段数对应于近似圆形部分的线数。