Introduction
In this lab, you will learn how to create a simple GUI using Matplotlib in Python. Specifically, you will create a Fourier Demo that displays two waveforms in the frequency and time domains. You will be able to adjust the frequency and amplitude of the waveforms by clicking and dragging on the plot.
VM Tips
After the VM startup is done, click the top left corner to switch to the Notebook tab to access Jupyter Notebook for practice.
Sometimes, you may need to wait a few seconds for Jupyter Notebook to finish loading. The validation of operations cannot be automated because of limitations in Jupyter Notebook.
If you face issues during learning, feel free to ask Labby. Provide feedback after the session, and we will promptly resolve the problem for you.
Import Libraries
The first step is to import the necessary libraries. We will be using Matplotlib, wxPython, and NumPy. Matplotlib is a plotting library for Python, wxPython is a GUI toolkit for Python, and NumPy is a library for numerical computing with Python.
import wx
import numpy as np
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg as FigureCanvas
from matplotlib.figure import Figure
Define Knob and Param Classes
The next step is to define the Knob and Param classes. These classes will be used to control the frequency and amplitude of the waveforms in the GUI.
class Knob:
"""
Knob - simple class with a "setKnob" method.
A Knob instance is attached to a Param instance, e.g., param.attach(knob)
Base class is for documentation purposes.
"""
def setKnob(self, value):
pass
class Param:
"""
The idea of the "Param" class is that some parameter in the GUI may have
several knobs that both control it and reflect the parameter's state, e.g.
a slider, text, and dragging can all change the value of the frequency in
the waveform of this example.
The class allows a cleaner way to update/"feedback" to the other knobs when
one is being changed. Also, this class handles min/max constraints for all
the knobs.
Idea - knob list - in "set" method, knob object is passed as well
- the other knobs in the knob list have a "set" method which gets
called for the others.
"""
def __init__(self, initialValue=None, minimum=0., maximum=1.):
self.minimum = minimum
self.maximum = maximum
if initialValue != self.constrain(initialValue):
raise ValueError('illegal initial value')
self.value = initialValue
self.knobs = []
def attach(self, knob):
self.knobs += [knob]
def set(self, value, knob=None):
self.value = value
self.value = self.constrain(value)
for feedbackKnob in self.knobs:
if feedbackKnob != knob:
feedbackKnob.setKnob(self.value)
return self.value
def constrain(self, value):
if value <= self.minimum:
value = self.minimum
if value >= self.maximum:
value = self.maximum
return value
Define SliderGroup Class
The SliderGroup class will create a slider and text field in the GUI for adjusting the frequency and amplitude of the waveforms.
class SliderGroup(Knob):
def __init__(self, parent, label, param):
self.sliderLabel = wx.StaticText(parent, label=label)
self.sliderText = wx.TextCtrl(parent, -1, style=wx.TE_PROCESS_ENTER)
self.slider = wx.Slider(parent, -1)
self.slider.SetRange(0, int(param.maximum * 1000))
self.setKnob(param.value)
sizer = wx.BoxSizer(wx.HORIZONTAL)
sizer.Add(self.sliderLabel, 0,
wx.EXPAND | wx.ALL,
border=2)
sizer.Add(self.sliderText, 0,
wx.EXPAND | wx.ALL,
border=2)
sizer.Add(self.slider, 1, wx.EXPAND)
self.sizer = sizer
self.slider.Bind(wx.EVT_SLIDER, self.sliderHandler)
self.sliderText.Bind(wx.EVT_TEXT_ENTER, self.sliderTextHandler)
self.param = param
self.param.attach(self)
def sliderHandler(self, event):
value = event.GetInt() / 1000.
self.param.set(value)
def sliderTextHandler(self, event):
value = float(self.sliderText.GetValue())
self.param.set(value)
def setKnob(self, value):
self.sliderText.SetValue(f'{value:g}')
self.slider.SetValue(int(value * 1000))
Define FourierDemoFrame Class
The FourierDemoFrame class will create the GUI using wxPython and Matplotlib.
class FourierDemoFrame(wx.Frame):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
panel = wx.Panel(self)
## create the GUI elements
self.createCanvas(panel)
self.createSliders(panel)
## place them in a sizer for the Layout
sizer = wx.BoxSizer(wx.VERTICAL)
sizer.Add(self.canvas, 1, wx.EXPAND)
sizer.Add(self.frequencySliderGroup.sizer, 0,
wx.EXPAND | wx.ALL, border=5)
sizer.Add(self.amplitudeSliderGroup.sizer, 0,
wx.EXPAND | wx.ALL, border=5)
panel.SetSizer(sizer)
def createCanvas(self, parent):
self.lines = []
self.figure = Figure()
self.canvas = FigureCanvas(parent, -1, self.figure)
self.canvas.callbacks.connect('button_press_event', self.mouseDown)
self.canvas.callbacks.connect('motion_notify_event', self.mouseMotion)
self.canvas.callbacks.connect('button_release_event', self.mouseUp)
self.state = ''
self.mouseInfo = (None, None, None, None)
self.f0 = Param(2., minimum=0., maximum=6.)
self.A = Param(1., minimum=0.01, maximum=2.)
self.createPlots()
self.f0.attach(self)
self.A.attach(self)
def createSliders(self, panel):
self.frequencySliderGroup = SliderGroup(
panel,
label='Frequency f0:',
param=self.f0)
self.amplitudeSliderGroup = SliderGroup(panel, label=' Amplitude a:',
param=self.A)
def mouseDown(self, event):
if self.lines[0].contains(event)[0]:
self.state = 'frequency'
elif self.lines[1].contains(event)[0]:
self.state = 'time'
else:
self.state = ''
self.mouseInfo = (event.xdata, event.ydata,
max(self.f0.value, .1),
self.A.value)
def mouseMotion(self, event):
if self.state == '':
return
x, y = event.xdata, event.ydata
if x is None: ## outside the axes
return
x0, y0, f0Init, AInit = self.mouseInfo
self.A.set(AInit + (AInit * (y - y0) / y0), self)
if self.state == 'frequency':
self.f0.set(f0Init + (f0Init * (x - x0) / x0))
elif self.state == 'time':
if (x - x0) / x0 != -1.:
self.f0.set(1. / (1. / f0Init + (1. / f0Init * (x - x0) / x0)))
def mouseUp(self, event):
self.state = ''
def createPlots(self):
self.subplot1, self.subplot2 = self.figure.subplots(2)
x1, y1, x2, y2 = self.compute(self.f0.value, self.A.value)
color = (1., 0., 0.)
self.lines += self.subplot1.plot(x1, y1, color=color, linewidth=2)
self.lines += self.subplot2.plot(x2, y2, color=color, linewidth=2)
self.subplot1.set_title(
"Click and drag waveforms to change frequency and amplitude",
fontsize=12)
self.subplot1.set_ylabel("Frequency Domain Waveform X(f)", fontsize=8)
self.subplot1.set_xlabel("frequency f", fontsize=8)
self.subplot2.set_ylabel("Time Domain Waveform x(t)", fontsize=8)
self.subplot2.set_xlabel("time t", fontsize=8)
self.subplot1.set_xlim([-6, 6])
self.subplot1.set_ylim([0, 1])
self.subplot2.set_xlim([-2, 2])
self.subplot2.set_ylim([-2, 2])
self.subplot1.text(0.05, .95,
r'$X(f) = \mathcal{F}\{x(t)\}$',
verticalalignment='top',
transform=self.subplot1.transAxes)
self.subplot2.text(0.05, .95,
r'$x(t) = a \cdot \cos(2\pi f_0 t) e^{-\pi t^2}$',
verticalalignment='top',
transform=self.subplot2.transAxes)
def compute(self, f0, A):
f = np.arange(-6., 6., 0.02)
t = np.arange(-2., 2., 0.01)
x = A * np.cos(2 * np.pi * f0 * t) * np.exp(-np.pi * t ** 2)
X = A / 2 * \
(np.exp(-np.pi * (f - f0) ** 2) + np.exp(-np.pi * (f + f0) ** 2))
return f, X, t, x
def setKnob(self, value):
x1, y1, x2, y2 = self.compute(self.f0.value, self.A.value)
self.lines[0].set(xdata=x1, ydata=y1)
self.lines[1].set(xdata=x2, ydata=y2)
self.canvas.draw()
Define App Class
The App class will create the application and display the GUI.
class App(wx.App):
def OnInit(self):
self.frame1 = FourierDemoFrame(parent=None, title="Fourier Demo",
size=(640, 480))
self.frame1.Show()
return True
Run the Application
The final step is to run the application.
if __name__ == "__main__":
app = App()
app.MainLoop()
Summary
In this lab, you learned how to create a simple GUI using Matplotlib in Python. You created a Fourier Demo that displays two waveforms in the frequency and time domains. You were able to adjust the frequency and amplitude of the waveforms by clicking and dragging on the plot.