Python| kivy 帆布

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桌面应用程序上使用。

???????? Kivy Tutorial – Learn Kivy with Examples.

帆布：
Canvas 是 Widget 用于绘制的根对象。 kivy 画布不是您绘画的地方。我一开始使用画布时遇到的主要问题是由于它的名称。特别是考虑到所有关于 HTML5 画布的嗡嗡声。我最初认为画布是油漆但画布基本上是一个指令的容器。
要使用 Canvas，您必须导入：

from kivy.graphics import Rectangle, Color

注意：默认情况下，Kivy 中的每个 Widget 都已经有一个 Canvas。创建小部件时，您可以创建绘图所需的所有指令。如果 self 是您当前的小部件。颜色和矩形指令会自动添加到画布对象中，并在绘制窗口时使用。

Basic Approach 
-> import kivy
-> import kivy App
-> import widget
-> import Canvas i.e.:
      from kivy.graphics import Rectangle, Color
-> set minimum version(optional)
-> Extend the Widget class
-> Create the App Class
-> return a Widget
-> Run an instance of the class

方法的实施——

Python3

# 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
 
# A Widget is the base building block
# of GUI interfaces in Kivy.
# It provides a Canvas that
# can be used to draw on screen.
from kivy.uix.widget import Widget
 
# From graphics module we are importing
# Rectangle and Color as they are
# basic building of canvas.
from kivy.graphics import Rectangle, Color
 
# class in which we are creating the canvas
class CanvasWidget(Widget):
     
    def __init__(self, **kwargs):
 
        super(CanvasWidget, self).__init__(**kwargs)
 
        # Arranging Canvas
        with self.canvas:
 
            Color(.234, .456, .678, .8)  # set the colour
 
            # Setting the size and position of canvas
            self.rect = Rectangle(pos = self.center,
                                  size =(self.width / 2.,
                                        self.height / 2.))
 
            # Update the canvas as the screen size change
            self.bind(pos = self.update_rect,
                  size = self.update_rect)
 
    # update function which makes the canvas adjustable.
    def update_rect(self, *args):
        self.rect.pos = self.pos
        self.rect.size = self.size
 
# Create the App Class
class CanvasApp(App):
    def build(self):
        return CanvasWidget()
 
# run the App
CanvasApp().run()

输出：

您还可以在画布中使用任何其他小部件。在下面的示例中，我们将展示如何添加图像并更改其颜色。
要更改颜色，只需更改将更改图像颜色的画布颜色。

Python3

# 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
 
# A Widget is the base building block
# of GUI interfaces in Kivy.
# It provides a Canvas that
# can be used to draw on screen.
from kivy.uix.widget import Widget
 
# From graphics module we are importing
# Rectangle and Color as they are
# basic building of canvas.
from kivy.graphics import Rectangle, Color
 
# class in which we are creating the canvas
class CanvasWidget(Widget):
     
    def __init__(self, **kwargs):
 
        super(CanvasWidget, self).__init__(**kwargs)
 
        # Arranging Canvas
        with self.canvas:
 
            Color(1, 0, 0, 1)  # set the colour
 
            # Setting the size and position of image
            # image must be in same folder
            self.rect = Rectangle(source ='download.jpg',
                                  pos = self.pos, size = self.size)
 
            # Update the canvas as the screen size change
            # if not use this next 5 line the
            # code will run but not cover the full screen
            self.bind(pos = self.update_rect,
                  size = self.update_rect)
 
    # update function which makes the canvas adjustable.
    def update_rect(self, *args):
        self.rect.pos = self.pos
        self.rect.size = self.size
 
# Create the App Class
class CanvasApp(App):
    def build(self):
        return CanvasWidget()
 
# run the App
CanvasApp().run()

输出：
App中使用的原图为：

画布中的图像：

笔记：
Kivy 绘图指令不会自动相对于小部件的位置或大小。因此，您在绘图时需要考虑这些因素。为了使您的绘图指令相对于小部件，指令需要在 KvLang 中声明或绑定到 pos 和 size 更改。