python - PyQt5 窗口中嵌入的 matplotlib 图形的 x 轴大小(以像素为单位)

Question

我在 PyQt5 窗口中有一个实时 matplotlib 图表:

您可以在此处阅读有关我如何使此代码工作的更多信息:
How to make a fast matplotlib live plot in a PyQt5 GUI

请将下面的代码复制粘贴到 python 文件中，并使用 Python 3.7 运行它:

#####################################################################################
#                                                                                   #
#                     PLOT A LIVE GRAPH IN A PYQT WINDOW                            #
#                                                                                   #
#####################################################################################

from __future__ import annotations
from typing import *
import sys
import os
from PyQt5 import QtWidgets, QtCore
from matplotlib.backends.backend_qt5agg import FigureCanvas
import matplotlib as mpl
import matplotlib.figure as mpl_fig
import matplotlib.animation as anim
import matplotlib.style as style
import numpy as np

style.use('ggplot')

class ApplicationWindow(QtWidgets.QMainWindow):
    '''
    The PyQt5 main window.

    '''
    def __init__(self):
        super().__init__()
        # 1. Window settings
        self.setGeometry(300, 300, 800, 400)
        self.setWindowTitle("Matplotlib live plot in PyQt")
        self.frm = QtWidgets.QFrame(self)
        self.frm.setStyleSheet("QWidget { background-color: #eeeeec; }")
        self.lyt = QtWidgets.QVBoxLayout()
        self.frm.setLayout(self.lyt)
        self.setCentralWidget(self.frm)

        # 2. Place the matplotlib figure
        self.myFig = MyFigureCanvas(x_len=200, y_range=[0, 100], interval=20)
        self.lyt.addWidget(self.myFig)

        # 3. Show
        self.show()
        return

class MyFigureCanvas(FigureCanvas, anim.FuncAnimation):
    '''
    This is the FigureCanvas in which the live plot is drawn.

    '''
    def __init__(self, x_len:int, y_range:List, interval:int) -> None:
        '''
        :param x_len:       The nr of data points shown in one plot.
        :param y_range:     Range on y-axis.
        :param interval:    Get a new datapoint every .. milliseconds.

        '''
        FigureCanvas.__init__(self, mpl_fig.Figure())
        # Range settings
        self._x_len_ = x_len
        self._y_range_ = y_range

        # Store two lists _x_ and _y_
        x = list(range(0, x_len))
        y = [0] * x_len

        # Store a figure and ax
        self._ax_  = self.figure.subplots()
        self._ax_.set_ylim(ymin=self._y_range_[0], ymax=self._y_range_[1])
        self._line_, = self._ax_.plot(x, y)

        # Call superclass constructors
        anim.FuncAnimation.__init__(self, self.figure, self._update_canvas_, fargs=(y,), interval=interval, blit=True)
        return

    def _update_canvas_(self, i, y) -> None:
        '''
        This function gets called regularly by the timer.

        '''
        y.append(round(get_next_datapoint(), 2))     # Add new datapoint
        y = y[-self._x_len_:]                        # Truncate list _y_
        self._line_.set_ydata(y)

        # Print size of bounding box (in pixels)
        bbox = self.figure.get_window_extent().transformed(self.figure.dpi_scale_trans.inverted())
        width, height = bbox.width * self.figure.dpi, bbox.height * self.figure.dpi
        print(f"bbox size in pixels = {width} x {height}")

        return self._line_,

# Data source
# ------------
n = np.linspace(0, 499, 500)
d = 50 + 25 * (np.sin(n / 8.3)) + 10 * (np.sin(n / 7.5)) - 5 * (np.sin(n / 1.5))
i = 0
def get_next_datapoint():
    global i
    i += 1
    if i > 499:
        i = 0
    return d[i]

if __name__ == "__main__":
    qapp = QtWidgets.QApplication(sys.argv)
    app = ApplicationWindow()
    qapp.exec_()

 

1。问题

我需要知道从 x_min 到 x_max 的像素数:

请注意，x 轴实际上超出了 x_min 和 x_max 边界。我不需要知道总长度。只是从 x_min 到 x_max 的长度。

 

2。到目前为止我尝试过的内容

我已经找到了一种获取图形边界框的方法。请注意 _update_canvas_() 函数中的以下代码行:

# Print size of bounding box (in pixels)
bbox = self.figure.get_window_extent().transformed(self.figure.dpi_scale_trans.inverted())
width, height = bbox.width * self.figure.dpi, bbox.height * self.figure.dpi
print(f"bbox size in pixels = {width} x {height}")

这给了我一个尺寸为 778.0 x 378.0 像素的边界框。这是一个很好的起点，但我不知道如何从这里继续。

我还注意到这个边界框大小从第一次开始就没有正确打印出来。第一次运行 _update_canvas_() 函数会打印出 640.0 x 480.0 像素的边界框，这是完全错误的。从第二次开始，打印尺寸是正确的。为什么？

 

编辑

我尝试了两种解决方案。第一个基于 @ImportanceOfBeingErnes 描述的方法(请参阅 Axes class - set explicitly size (width/height) of axes in given units )，第二个基于 @Eyllanesc 的答案。

#####################################################################################
#                                                                                   #
#                PLOT A LIVE GRAPH IN A PYQT WINDOW                                 #
#                                                                                   #
#####################################################################################

from __future__ import annotations
from typing import *
import sys
import os
from PyQt5 import QtWidgets, QtCore
from matplotlib.backends.backend_qt5agg import FigureCanvas
import matplotlib as mpl
import matplotlib.figure as mpl_fig
import matplotlib.animation as anim
import matplotlib.style as style
import numpy as np

style.use('ggplot')

def get_width_method_a(ax, dpi, canvas):
    l = float(ax.figure.subplotpars.left)
    r = float(ax.figure.subplotpars.right)
    x, y, w, h = ax.figure.get_tightbbox(renderer=canvas.get_renderer()).bounds
    return float(dpi) * float(w - (l + r))

def get_width_eyllanesc(ax):
    """ Based on answer from @Eyllanesc"""
    """ See below """
    y_fake = 0
    x_min, x_max = 0, 200
    x_pixel_min, _ = ax.transData.transform((x_min, y_fake))
    x_pixel_max, _ = ax.transData.transform((x_max, y_fake))
    return x_pixel_max - x_pixel_min

class ApplicationWindow(QtWidgets.QMainWindow):
    '''
    The PyQt5 main window.

    '''
    def __init__(self):
        super().__init__()
        # 1. Window settings
        self.setGeometry(300, 300, 800, 400)
        self.setWindowTitle("Matplotlib live plot in PyQt")
        self.frm = QtWidgets.QFrame(self)
        self.frm.setStyleSheet("QWidget { background-color: #eeeeec; }")
        self.lyt = QtWidgets.QVBoxLayout()
        self.frm.setLayout(self.lyt)
        self.setCentralWidget(self.frm)

        # 2. Place the matplotlib figure
        self.myFig = MyFigureCanvas(x_len=200, y_range=[0, 100], interval=20)
        self.lyt.addWidget(self.myFig)

        # 3. Show
        self.show()
        return

class MyFigureCanvas(FigureCanvas, anim.FuncAnimation):
    '''
    This is the FigureCanvas in which the live plot is drawn.

    '''
    def __init__(self, x_len:int, y_range:List, interval:int) -> None:
        '''
        :param x_len:       The nr of data points shown in one plot.
        :param y_range:     Range on y-axis.
        :param interval:    Get a new datapoint every .. milliseconds.

        '''
        FigureCanvas.__init__(self, mpl_fig.Figure())
        # Range settings
        self._x_len_ = x_len
        self._y_range_ = y_range

        # Store two lists _x_ and _y_
        x = list(range(0, x_len))
        y = [0] * x_len

        # Store a figure and ax
        self._ax_  = self.figure.subplots()
        self._ax_.set_ylim(ymin=self._y_range_[0], ymax=self._y_range_[1])
        self._line_, = self._ax_.plot(x, y)
        self._line_.set_ydata(y)
        print("")
        print(f"width in pixels (first call, method is 'method_a')  = {get_width_method_a(self._ax_, self.figure.dpi, self)}")
        print(f"width in pixels (first call, method is 'eyllanesc') = {get_width_eyllanesc(self._ax_)}")

        # Call superclass constructors
        anim.FuncAnimation.__init__(self, self.figure, self._update_canvas_, fargs=(y,), interval=interval, blit=True)
        return

    def _update_canvas_(self, i, y) -> None:
        '''
        This function gets called regularly by the timer.

        '''
        y.append(round(get_next_datapoint(), 2))     # Add new datapoint
        y = y[-self._x_len_:]                        # Truncate list _y_
        self._line_.set_ydata(y)
        print("")
        print(f"width in pixels (method is 'method_a')  = {get_width_method_a(self._ax_, self.figure.dpi, self)}")
        print(f"width in pixels (method is 'eyllanesc') = {get_width_eyllanesc(self._ax_)}")
        return self._line_,

# Data source
# ------------
n = np.linspace(0, 499, 500)
d = 50 + 25 * (np.sin(n / 8.3)) + 10 * (np.sin(n / 7.5)) - 5 * (np.sin(n / 1.5))
i = 0
def get_next_datapoint():
    global i
    i += 1
    if i > 499:
        i = 0
    return d[i]

if __name__ == "__main__":
    qapp = QtWidgets.QApplication(sys.argv)
    app = ApplicationWindow()
    qapp.exec_()

结论:
正确答案是550 像素，这是我在打印屏幕上测量的值。现在，当我运行程序时，我得到以下输出:

width in pixels (first call, method is 'method_a')  = 433.0972222222222
width in pixels (first call, method is 'eyllanesc') = 453.1749657377798

width in pixels (method is 'method_a')  = 433.0972222222222
width in pixels (method is 'eyllanesc') = 453.1749657377798

width in pixels (method is 'method_a')  = 540.0472222222223
width in pixels (method is 'eyllanesc') = 550.8908177249887

...

这两种方法的第一次调用给出了错误的结果。从第三次(!)调用开始，它们都给出了相当好的结果，@Eyllanesc 的方法是获胜者。

如何解决第一次调用结果错误的问题？

Answer 1

对于 old answer我必须进行计算，在你的例子中是:

y_fake = 0
x_min, x_max = 0, 200
x_pixel_min, _ = self._ax_.transData.transform((x_min, y_fake))
x_pixel_max, _ = self._ax_.transData.transform((x_max, y_fake))

print(
    f"The length in pixels between x_min: {x_min} and x_max: {x_max} is: {x_pixel_max - x_pixel_min}"
)

注意:

计算考虑了绘制的内容，因此在最初的时刻它仍在绘制，因此结果是正确的，但我们的眼睛无法区分它们。如果你想在没有动画的情况下获得正确的尺寸，则必须在绘画稳定时计算该值，这很难计算，解决方法是使用 QTimer 稍后进行测量:

    # ...
    self._ax_ = self.figure.subplots()
    self._ax_.set_ylim(ymin=self._y_range_[0], ymax=self._y_range_[1])
    self._line_, = self._ax_.plot(x, y)

    QtCore.QTimer.singleShot(100, self.calculate_length)
    # ...

def calculate_length(self):
    y_fake = 0
    x_min, x_max = 0, 200
    x_pixel_min, _ = self._ax_.transData.transform((x_min, y_fake))
    x_pixel_max, _ = self._ax_.transData.transform((x_max, y_fake))

    print(
        f"The length in pixels between x_min: {x_min} and x_max: {x_max} is: {x_pixel_max - x_pixel_min}"
    )