如何更改已在 Python3 Kivy 中绘制的矩形的颜色？

Question

我正在尝试了解如何使用 Kivy - 特别是画布。我或多或少了解如何移动和调整已经绘制的矩形的大小，但我无法让矩形改变颜色。这是我的代码：

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.graphics import Rectangle, Color


class CanvasWidget(Widget):

    def __init__(self, **kwargs):
        super(CanvasWidget, self).__init__(**kwargs)
        self.click_occured = False
        with self.canvas:
            Color(0, 1, 0)
            self.background = Rectangle(pos=self.pos, size=self.size)
            Color(1, 1, 1)
            self.rect1 = Rectangle(pos=self.pos, size=(self.width/2, self.height/2))
            Color(0, 0, 1)
            self.rect2 = Rectangle(pos=self.pos, size=(self.width/4, self.height/4))
            self.bind(pos = self.update_rect, size = self.update_rect)

    def update_rect(self, *args):
        self.background.pos = self.pos
        self.background.size = self.size
        if not self.click_occured:
            self.rect1.pos = self.pos
        else:
            self.rect1.pos = self.x + self.width/8, self.y + self.height/8
        self.rect1.size = (self.width/2, self.height/2)
        self.rect2.pos = self.pos
        self.rect2.size = (self.width/4, self.height/4)

    def on_touch_down(self, touch):
        self.click_occured = True
        self.rect1.pos = self.x + self.width/8, self.y + self.height/8
        #also, change rect1's color from white to red


class CanvasApp(App):
    def build(self):
        return CanvasWidget()
CanvasApp().run()

代替

on_touch_down

方法末尾的注释，我想将

rect1

的颜色更改为红色。它必须是对现有矩形的更改，而不是创建新矩形，因为我希望它保留在

rect2

后面，并且我不想手动重绘后者。 如果可能的话，我希望在不使用 kv 语言的情况下实现这一目标，因为我希望能够在代码运行时动态创建矩形、标签等，而这对于 kv 语言似乎不方便。

Answer 1

您可以使用图形指令组来完成您想要的事情。首先，为涉及的画布指令创建一个

InstructionGroup

，如下所示：

    # create an instruction group for the white Rectangle
    self.grp1 = InstructionGroup()
    self.grp1.add(Color(1, 1, 1))
    self.rect1 = Rectangle(pos=self.pos, size=(self.width/2, self.height/2))
    self.grp1.add(self.rect1)

然后使用

self.canvas.add(self.grp1)

将该组添加到画布。

然后您可以通过删除/添加指令来修改该组：

    self.grp1.remove(self.grp1.children[0])  # remove the color instruction
    self.grp1.insert(0, Color(1, 0, 0))  # insert the new color

这是使用此方法的代码的修改版本：

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.graphics import Rectangle, Color, InstructionGroup


class CanvasWidget(Widget):

    def __init__(self, **kwargs):
        super(CanvasWidget, self).__init__(**kwargs)
        self.click_occured = False

        # create an instruction group for the white Rectangle
        self.grp1 = InstructionGroup()
        self.grp1.add(Color(1, 1, 1))
        self.rect1 = Rectangle(pos=self.pos, size=(self.width/2, self.height/2))
        self.grp1.add(self.rect1)

        with self.canvas:
            Color(0, 1, 0)
            self.background = Rectangle(pos=self.pos, size=self.size)
            self.canvas.add(self.grp1)  # add the instruction group to the canvas
            Color(0, 0, 1)
            self.rect2 = Rectangle(pos=self.pos, size=(self.width/4, self.height/4))
            self.bind(pos = self.update_rect, size = self.update_rect)

    def update_rect(self, *args):
        self.background.pos = self.pos
        self.background.size = self.size
        if not self.click_occured:
            self.rect1.pos = self.pos
        else:
            self.rect1.pos = self.x + self.width/8, self.y + self.height/8
        self.rect1.size = (self.width/2, self.height/2)
        self.rect2.pos = self.pos
        self.rect2.size = (self.width/4, self.height/4)

    def on_touch_down(self, touch):
        self.click_occured = True
        self.grp1.remove(self.grp1.children[0])  # remove the color instruction
        self.grp1.insert(0, Color(1, 0, 0))  # insert the new color
        self.rect1.pos = self.x + self.width/8, self.y + self.height/8
        #also, change rect1's color from white to red


class CanvasApp(App):
    def build(self):
        return CanvasWidget()
CanvasApp().run()