在 Kivy 中程序 运行 时如何重绘 canvas？

Question

我希望程序根据用户输入的两个值的比率重画线

我试过这个算法： 我有两个变量 pulse_length 和 distance_length。 these two points的坐标依比例=(distance_length/(distance_length+pulse_length)*540)+40

当我调用 TextInput 对象的 on_text_validate 事件时，我将输入的值写入变量并重绘 canvas。重绘canvas我用了self.canvas.ask_update()，但是不行

这里是简化的程序代码：

# input variables
pulse_length = 499
distance_length = 999

# calculations
ratio = (distance_length / (distance_length + pulse_length) * 540) + 40

class Line(Widget):
    def __init__(self, **kwargs):
        super(Line, self).__init__(**kwargs)
        with self.canvas:
            kg.Line(
                points=(
                    20, 350,
                    40, 350,
                    40, 240,
                    ratio, 240,
                    ratio, 350,
                    560, 350,
                    560, 240,
                    620, 240),

            # Other instructions ...

            Callback(self.update)
    def update(self, inst):
        ratio = (distance_length / (distance_length + pulse_length) * 540) + 40
        self.canvas.ask_update()

class TextInputGrid(Widget):
    def __init__(self, **kwargs):
        super(TextInputGrid, self).__init__(**kwargs)

        self.inputlayout = GridLayout(cols=1, size=(100, 30))
        self.inputlayout.textfield = TextInput(multiline=False)
        self.inputlayout.add_widget(self.inputlayout.textfield)

class MyFloatLayout(FloatLayout):
    def __init__(self, **kwargs):
        super(FloatLayout, self).__init__(**kwargs)

        # Drawn line widget
        self.add_widget(Line())

        # TextInput 1
        self.textinput1 = TextInputGrid()
        self.textinput1.inputlayout.textfield.bind(on_text_validate=self.enter_pulse)

        # TextInput 2
        self.textinput2 = TextInputGrid()
        self.textinput2.inputlayout.textfield.bind(on_text_validate=self.enter_distance)

        self.add_widget(self.textinput1.inputlayout)
        self.add_widget(self.textinput2.inputlayout)

    def enter_pulse(self, instance):
        global pulse_length
        pulse_length = int(self.textinput1.inputlayout.textfield.text)

    def enter_distance(self, instance):
        global distance_length
        distance_length = int(self.textinput2.inputlayout.textfield.text)


class GeneratorApp(App):
    def build(self):
        return MyFloatLayout()


if __name__ == '__main__':
    GeneratorApp().run()

也许我不知道 ask_update() 是如何工作的？如果是，请解释如何重绘 canvas。或者如果算法不正确，请告诉我如何实现这样的程序。

Answer 1

我发现 kg 是 Kivy.graphics。

当您在 Canvas 指令中使用 ratio 时，它使用 ratio 的当前值，并且不记得该值来自何处。因此，更改 ratio 的当前值不会更改 Line。为了更新 Line，您需要重新绘制它。这是对您的代码的修改，它删除了旧的 Line 并绘制了一个新版本：

from kivy.app import App
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.gridlayout import GridLayout
from kivy.uix.textinput import TextInput
from kivy.uix.widget import Widget
import kivy.graphics as kg

# input variables
pulse_length = 499
distance_length = 999

class Line(Widget):
    def __init__(self, **kwargs):
        ratio = (distance_length / (distance_length + pulse_length) * 540) + 40
        super(Line, self).__init__(**kwargs)
        with self.canvas:
            self.line = kg.Line(
                points=(
                    20, 350,
                    40, 350,
                    40, 240,
                    ratio, 240,
                    ratio, 350,
                    560, 350,
                    560, 240,
                    620, 240))

            # Other instructions ...

            #Callback(self.update)
    def update(self):
        ratio = (distance_length / (distance_length + pulse_length) * 540) + 40
        self.canvas.remove(self.line)
        with self.canvas:
            self.line = kg.Line(
                points=(
                    20, 350,
                    40, 350,
                    40, 240,
                    ratio, 240,
                    ratio, 350,
                    560, 350,
                    560, 240,
                    620, 240))

class TextInputGrid(Widget):
    def __init__(self, **kwargs):
        super(TextInputGrid, self).__init__(**kwargs)

        self.inputlayout = GridLayout(cols=1, size=(100, 30))
        self.inputlayout.textfield = TextInput(multiline=False)
        self.inputlayout.add_widget(self.inputlayout.textfield)

class MyFloatLayout(FloatLayout):
    def __init__(self, **kwargs):
        super(FloatLayout, self).__init__(**kwargs)

        # Drawn line widget
        self.line = Line()
        self.add_widget(self.line)

        # TextInput 1
        self.textinput1 = TextInputGrid(pos=(0,0))
        self.textinput1.inputlayout.textfield.bind(on_text_validate=self.enter_pulse)

        # TextInput 2
        self.textinput2 = TextInputGrid(pos=(100,100))
        self.textinput2.inputlayout.textfield.bind(on_text_validate=self.enter_distance)

        self.add_widget(self.textinput1.inputlayout)
        self.add_widget(self.textinput2.inputlayout)

    def enter_pulse(self, instance):
        global pulse_length
        pulse_length = int(self.textinput1.inputlayout.textfield.text)
        self.line.update()

    def enter_distance(self, instance):
        global distance_length
        distance_length = int(self.textinput2.inputlayout.textfield.text)
        self.line.update()


class GeneratorApp(App):
    def build(self):
        return MyFloatLayout()


if __name__ == '__main__':
    GeneratorApp().run()