Kivy：绘制到小部件

Question

我收集了 kivy 的经验，但在使用小部件中心时遇到了问题。 我的问题显示了下一个脚本：

from kivy.uix.button import Button
from kivy.uix.widget import Widget
from kivy.uix.boxlayout import BoxLayout
from kivy.app import App
from functools import partial
from kivy.graphics import Color, Ellipse

class CanvasApp(App):

    def draw(self,wid, color):
         with wid.canvas:
            Color(color[0], color[1], color[2])
            Ellipse(size= (100, 100), pos=(wid.center_x, wid.center_y))
         return

    def painter(self, wid, *largs):
        self.draw(wid, (0,  1, 0))
        return

    def build(self):
        wid = Widget()

        btn_painter = Button(text='Painter',
                            on_press=partial(self.painter, wid))

        ctrl =  BoxLayout(size_hint=(1, None), height=50)
        ctrl.add_widget(btn_painter)
        root = BoxLayout(orientation='vertical')
        root.add_widget(wid)
        root.add_widget(ctrl)

        self.draw(wid, (1, 0, 0))
        return root

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

我想在不使用按钮画家的情况下在小部件中心（黑色矩形）绘制圆圈。 我无法获得中心的实际中心坐标。 不使用按钮仅可用默认中心坐标。 OK过程如何？ 谢谢你的回答。

Answer 1

问题是在build()方法中尚未设置wid大小和位置。 所以你需要稍微延迟draw()的调用。 尝试将调用draw()替换为：

    Clock.schedule_once(partial(self.draw, wid, (1,0,0)))

您还需要稍微更改draw()方法以处理添加的dt参数：

def draw(self,wid, color, *args):

Answer 2

我找到了我的问题的解决方案。 所有解释遵循脚本：

from kivy.app import App
from kivy.graphics import Color, Rectangle, Ellipse
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button


class DrawArea(FloatLayout):

    def __init__(self, **kwargs):
        # make sure we aren't overriding any important functionality
        super(DrawArea, self).__init__(**kwargs)
        self.rect1 = None
        self.li_item = []
        return

    def clear_area(self):                
        for item in self.li_item:
            self.canvas.remove(item)
        self.li_item.clear()

    def draw_rect(self):
        with self.canvas:

            Color(0, 1, 0, 1)  # green; colors range from 0-1 not 0-255
            self.rect1 = Rectangle(size=self.size, pos=self.pos)

            Color(1, 0, 0, 1)  # green; colors range from 0-1 not 0-255
            width  = self.width/2
            height = self.height/2 
            pos_x = self.center_x -width/2
            pos_y = self.center_y - height/2
            self.rect2 = Rectangle(size=(width, height), pos=(pos_x, pos_y))
            self.li_item.append(self.rect1)
            self.li_item.append(self.rect2)

        return

    def draw_circle(self):
        Color(1, 0, 0)
        d = 120
        with self.canvas:
            Color(0, 1, 0)
            self.circle1 = Ellipse(size = (d,d), pos = (self.center_x-d/2, self.center_y-d/2))
            Color(0, 0, 1)
            self.circle2 = Ellipse(size = (d/2,d/2), pos = (self.center_x - self.size[0]/2, self.center_y - self.size[1]/2))
            self.li_item.append(self.circle1)
            self.li_item.append(self.circle2)
        return

class MainApp(App):

    def build(self):
        self.task = 'circle'


        root = BoxLayout(orientation = 'vertical')
        self.dra = DrawArea()
        button = Button(text = 'painter',size_hint=(1, None), height=50, on_press = self.but_paint)

        root.add_widget(self.dra)
        root.add_widget(button)

        if self.task == 'circle':
            self.dra.bind(pos = self._update_circ, size = self._update_circ)
            self.dra.draw_circle()
        else:
            self.dra.bind(size=self._update_rect, pos=self._update_rect)
            self.dra.draw_rect()

        return root

    def but_paint(self, instance):
        #self.dra.clear_area()

        if self.task == 'circle':
            self.task = 'rectangle'
        else:
            self.task = 'circle'

        if self.task == 'circle':
            self.dra.bind(pos = self._update_circ, size = self._update_circ)
            self.dra.draw_circle()
        else:
            self.dra.bind(size=self._update_rect, pos=self._update_rect)
            self.dra.draw_rect()

        return

    def _update_circ(self, instance, value):
        d = 120
        pos1_x = instance.center[0] -d/2
        pos1_y = instance.center[1] -d/2

        self.dra.circle1.pos = (pos1_x, pos1_y)

        pos2_x = instance.center[0] - instance.size[0]/2
        pos2_y = instance.center[1] - instance.size[1]/2

        self.dra.circle2.pos = (pos2_x, pos2_y)

        return

    def _update_rect(self, instance, value):
        if self.dra.rect1 != None:
            self.dra.rect1.pos = instance.pos
            self.dra.rect1.size = instance.size

        width  = instance.size[0]/2
        height = instance.size[1]/2 
        pos_x = instance.center[0] -width/2
        pos_y = instance.center[1] - height/2

        self.dra.rect2.pos = (pos_x, pos_y)
        self.dra.rect2.size = (width, height)


    def draw_rect(self):
        with self.dra.canvas.before:
            Color(0, 1, 0, 1)  # green; colors range from 0-1 not 0-255
            self.rect1 = Rectangle(size=self.dra.size, pos=self.dra.pos)

            Color(1, 0, 0, 1)  # green; colors range from 0-1 not 0-255
            width  = self.width/2
            height = self.height/2 
            self.rect2 = Rectangle(size=(width, height), pos=(self.center_x -width/2, self.center_y - height/2))

        return

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