基于6_button.py

Question

我试图通过从一个点拖动到窗口的另一个点来用鼠标画一条线。我也想在拖动的时候代表这条线。就像在旧的MS PaintBrush中画一条线一样。

我的问题是我只能通过不断删除旧的Line并在画布中添加 new 顶点指令来实现这一目标。但是，我无法更新现有说明。甚至没有添加和删除相同的指令。它必须是Line的新实例。您可以通过运行以下代码来查看我想要的结果。如果您尝试使用注释行运行它，它将不再起作用。

from kivy.app import App
from kivy.uix.relativelayout import RelativeLayout
from kivy.graphics import Line

class MyCanvas(RelativeLayout):
    def on_touch_down(self, touch):
        with self.canvas:
            self.line = Line(points=[touch.x,touch.y,touch.x+1,touch.y+1])
        self.bind(on_touch_move=self.update_line, on_touch_up=self.end_line)
        return True

    def update_line(self, instance, touch):
        self.line.points[2] = touch.x
        self.line.points[3] = touch.y
        self.canvas.remove(self.line)
#        self.canvas.add(self.line) # - this doesn't work
#        self.canvas.ask_update()   # - not even using this
        with self.canvas:
            self.line = Line(points=self.line.points) # this works

    def end_line(self, instance, touch):
        self.unbind(on_touch_move=self.update_line)
        self.unbind(on_touch_up=self.end_line)
        self.line.points[2] = touch.x
        self.line.points[3] = touch.y
        self.canvas.remove(self.line)
#        self.canvas.add(self.line) # - this doesn't work
#        self.canvas.ask_update()   #- not even using this
        self.canvas.add(Line(points=self.line.points))  # this way works

class ExampleApp(App):
    def build(self):
        return MyCanvas()

ExampleApp().run()

我还尝试使用带有Color指令的建议in this other question的Kivy属性。它不起作用，有another question related to it。

Answer 1

我正在努力解决同样的问题。我从kivy / guide / firstwidget目录中的6_button.py示例开始

我找到了一些有用的东西（使用pop两次从点中移除最后一个x，y对）但我认为这很尴尬，请参阅下面的代码。我希望有人可以告诉我们如何正确“更新”。

基于6_button.py

from random import random
from kivy.app import App
from kivy.uix.widget import Widget
from kivy.uix.button import Button
from kivy.graphics import Color, Ellipse, Line


class MyPaintWidget(Widget):

    def on_touch_down(self, touch):
        color = (random(), 1, 1)
        with self.canvas:
            Color(*color, mode='hsv')
            d = 10.
            Ellipse(pos=(touch.x - d / 2, touch.y - d / 2), size=(d, d))
            touch.ud['line'] = Line(points=(touch.x, touch.y, touch.x+30, touch.y))
            #print(dir(touch.ud['line']))

    def on_touch_move(self, touch):
        #touch.ud['line'].points += [touch.x, touch.y]
        touch.ud['line'].points.pop()                     #
        touch.ud['line'].points.pop()                     # works but is awkward
        touch.ud['line'].points += [touch.x, touch.y]     #

        #touch.ud['line'].points[2:4] = [touch.x, touch.y] 
        #self.canvas.ask_update()              # no error but didnt work
        #touch.ud['line'].ask_update()         # didnt work
        #print(touch.ud['line'].points)
        #touch.ud['line'].needs_redraw()       # error 'bool not callable'
        #touch.ud['line'].needs_redraw = True  # error 'not writable'
        #touch.ud['line'].needs_redraw         #no error but doesnt work


class MyPaintApp(App):

    def build(self):
        parent = Widget()
        painter = MyPaintWidget()
        clearbtn = Button(text='Clear')
        parent.add_widget(painter)
        parent.add_widget(clearbtn)

        def clear_canvas(obj):
            painter.canvas.clear()
        clearbtn.bind(on_release=clear_canvas)

        return parent


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

为什么我需要创建一个Line的新实例，而不是简单地在Kivy中更新或添加和删除它

1 个答案:

基于6_button.py