嵌入到Ubuntu 18.04的PyQt5 GUI中的Matplotlib图形无法按照设置的透明度进行渲染

Question

通过使用Matplotlib提供的“ Qt5Agg”后端，我将实时图形嵌入到PyQt5 GUI中。这是定义GUI和实时图的工作的代码。

import matplotlib
matplotlib.use('Qt5Agg')
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure

import random
import collections
import time
from PyQt5 import QtWidgets


class LiveGraphCanvas(FigureCanvas):
    def __init__(self, parent=None, height=5, width=4, dpi=100):
        fig = Figure(figsize=(height, width), dpi=dpi)
        fig.set_tight_layout(True)
        fig.patch.set_alpha(0.0)

        self.axes = fig.add_subplot(111)
        self.axes.set_xlabel("Data Points")
        self.axes.set_ylabel("Trim width (um)")
        self.axes.grid(True)

        FigureCanvas.__init__(self, fig)
        self.setParent(parent)

        FigureCanvas.setSizePolicy(self, QtWidgets.QSizePolicy.Expanding, QtWidgets.QSizePolicy.Expanding)
        FigureCanvas.updateGeometry(self)

    # Function which will later be defined by the child-class
    def compute_initial_figure(self):
        pass


class LiveGraphWidget(LiveGraphCanvas):
    def __init__(self, max_points, *args, **kwargs):
        LiveGraphCanvas.__init__(self, *args, **kwargs)
        self.data_length = max_points
        self.data_points = collections.deque([0 for i in range(self.data_length)], maxlen=self.data_length)

    def compute_initial_figure(self):
        self.axes.plot([i for i in range(0, self.data_length)], [random.randint(1000, 6000) for i in range(0, self.data_length)], 'r')

    def update_figure(self, data_point):
        start_time = time.time()
        self.data_points.append(data_point)
        self.axes.cla()
        self.axes.plot(self.data_points, 'r')
        self.axes.set_xlabel("Data Points")
        self.axes.set_ylabel("Trim width (um)")
        self.axes.grid(True)
        self.draw()
        print ("Plot Update Time (ms): ", (time.time() - start_time)*1000)

然后创建LiveGraphWidget类的对象，并将其添加到主类的QVBoxLayout中。我想要在图形后面使用透明的Canvas，所以在LiveGraphCanvas类中将Alpha透明度设置为0。在Windows 10上，该图形会根据设置的alpha值正确显示，如下所示：

但是，在Ubuntu 18.04上，alpha参数不起作用，并且图形后面出现了难看的白色背景：

（请忽略两个屏幕截图之间的颜色和形状的差异，因为两者都是使用不同的软件拍摄的）

透明性无法正常工作的原因可能是什么？是由于Ubuntu的内部GUI限制还是Matplotlib不适用于该平台？