Crash issues in wxPython with matplotlib when processing extensive image sequences

Frontend and Backend Development
1

Encountering a wxPython assertion error with matplotlib when handling a large sequence of images. Below is alternate sample code:

import wx
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg as CanvasWidget

class ImagePanel(wx.Panel):
    def __init__(self, parent):
        super().__init__(parent)
        self.fig = plt.Figure(facecolor='dimgray')
        self.canvas = CanvasWidget(self, -1, self.fig)
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(self.canvas, 1, wx.EXPAND)
        self.SetSizer(sizer)
    
    def display_image(self, image):
        self.fig.clear()
        ax = self.fig.add_subplot(111)
        ax.imshow(image, cmap='viridis')
        ax.axis('off')
        self.canvas.draw()

class MainWindow(wx.Frame):
    def __init__(self):
        super().__init__(None, title='Process Stack')
        self.panel = ImagePanel(self)
        self.start_btn = wx.Button(self, label='Start')
        self.progress = wx.Gauge(self, range=10)
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(self.panel, 1, wx.EXPAND)
        sizer.Add(self.start_btn, 0, wx.ALL | wx.CENTER, 5)
        sizer.Add(self.progress, 0, wx.EXPAND | wx.ALL, 5)
        self.SetSizer(sizer)
        self.start_btn.Bind(wx.EVT_BUTTON, self.run_process)
        self.Show()
    
    def run_process(self, event):
        img_stack = np.random.rand(10, 100, 100)
        for idx, img in enumerate(img_stack):
            self.panel.display_image(img)
            self.progress.SetValue(idx + 1)

if __name__ == '__main__':
    app = wx.App(False)
    MainWindow()
    app.MainLoop()
2

hey, i had similar crashs with extensive image sequences. i solved it by reinitializing the plot instead of constantly clearing it. pacing the updtaing process also helps to avoid call stacking. hope this workaround helps.

3

hey, have u tried caching axes or using idle events to handle heavy processing? i experemented with offloading operations using wx.IdleEvent, and it helped a bit. any of u had similar results? curious to hear more!

4

The crashes could be alleviated by implementing deferred rendering using a timer. In my work, a wx.Timer call to update the canvas in intervals instead of embedding a loop within a callback reduced the likelihood of encountering wxPython assertion errors. By isolating the rendering function and ensuring that each update completes before the next begins, potential race conditions are minimized. This approach proved effective even when processing larger sequences, and it enabled more predictable behavior in the user interface without significant overhead.

5

The crash might be linked to how the drawing updates are managed across successive updates. In my experience, ensuring that the GUI thread isn’t blocked by heavy computational work helps alleviate these issue. One effective approach is to separate image processing from the drawing process, using thread-safe calls to update the display. Utilizing a timer or wx.CallAfter for invoking canvas redraw can prevent resource contention in the UI thread. Experimenting with these methods has helped stabilize similar applications for me under high load.

6

hey all, i found using wx.CallAfter to trigger the canvas redraw helped. by decoupling the image update from heavy processing the ui didn’t choke. give it a try if your thread’s getting too crowded, might just solve it.