wxPython listctrl flickers with rapid updates

Question

I'm putting some lines in a list control and then updating them fairly quickly - normally the data comes in from a bus - and the whole list flickers quite a lot. It would be really nice to stop it doing that.

I've cut down the code as much as I can while still keeping the general look of what I'm doing in the sample below.

It doesn't seem to matter if the lisctrl is in a wx.Notebook or just a plain wx.Panel so I left the notebook there.

I've started to look at double buffering but wanted to see if there was something else to try first.

Doing this on Windows 7 with wxPython 2.8.12.1. Happens on XP as well though.

import sys
import time
import logging
import wx
from random import randint

UPDATE_MS=10

class CanMsg(object):
    def __init__(self, ID, type, len, data=None):
        """Represents a CAN message"""
        self.ID=ID          # 11/29-bit message identifier
        self.MSGTYPE=type # Type of the message
        self.LEN=len          # Data Length Code of the message (0..8)
        if data:
            self.DATA=data
        else:
            self.DATA=[0,]*len

class EmulatorFrame(wx.Frame):
    def __init__(self, parent, id, title, pos=wx.DefaultPosition, size=wx.DefaultSize, 
                                style=wx.DEFAULT_FRAME_STYLE):
        wx.Frame.__init__(self, parent, id, title, pos, size, style)
        # create frame menu and status bar
        self.status = self.CreateStatusBar()
        # create tab panels
        panel = wx.Panel(self)
        nb = wx.Notebook(panel)
        self.messages_tab = MessagesTab(nb)
        # self.messages_tab = MessagesTab(panel)
        # add tab pages to notebook
        nb.AddPage(self.messages_tab, 'CAN data')
        self._nb = nb

        sizer = wx.BoxSizer()
        sizer.Add(nb, 1, wx.EXPAND)
        # sizer.Add(self.messages_tab, 1, wx.EXPAND)
        minSize=self.ClientToWindowSize(sizer.GetMinSize())     # get this as Info tab's min size is too small
        panel.SetSizerAndFit(sizer)
        self.SetInitialSize(minSize)

        self.InitialiseTimers()

    def InitialiseTimers(self):
        # tab updates and test comparison timer
        self.displayTimer=wx.Timer(self)
        self.Bind(wx.EVT_TIMER, self.OnRefresh, self.displayTimer)
        self.displayTimer.Start(UPDATE_MS)
        # self.Bind(wx.EVT_IDLE, self.OnRefresh)

    def OnRefresh(self, event):
        self.messages_tab.Update(can_send, can_recv)

class MessagesTab(wx.Panel):
    def __init__(self, parent):
        msg_size=450    # width of messge windows
        wx.Panel.__init__(self, parent, wx.ID_ANY)

        receivedLabel=wx.StaticText(self, wx.ID_ANY, 'Messages Received')
        receivedLabel.SetForegroundColour('blue')
        sentLabel=wx.StaticText(self, wx.ID_ANY, 'Messages Sent')
        sentLabel.SetForegroundColour('dark slate blue')
        SentMsgList = MessageList(self, size=wx.Size(msg_size,150))
        ReceivedMsgList = MessageList(self, size=wx.Size(msg_size,150))

        sizer=wx.BoxSizer(wx.VERTICAL)
        sizer.Add(sentLabel, 0, wx.EXPAND|wx.ALL, 2)
        sizer.Add(SentMsgList, 1, wx.EXPAND|wx.ALL, 2)
        sizer.Add(receivedLabel, 0, wx.EXPAND|wx.ALL, 2)
        sizer.Add(ReceivedMsgList, 1, wx.EXPAND|wx.ALL, 2)

        b = wx.Button(self, wx.ID_ANY, 'Clear messages', name='clear_stale')
        self.Bind(wx.EVT_BUTTON, self.OnClearMessages, b)
        sizer.Add(b, proportion=0, flag=wx.ALL, border=4)

        self.SetSizer(sizer)
        self.SentMsgList = SentMsgList
        self.ReceivedMsgList = ReceivedMsgList

    def Update(self, can_send, can_recv):
        self.SentMsgList.Populate(can_send)
        self.ReceivedMsgList.Populate(can_recv)

    def OnClearMessages(self, event):
        self.SentMsgList.DeleteAllItems()
        self.ReceivedMsgList.DeleteAllItems()

class MessageList(wx.ListCtrl):
    def __init__(self, parent, ID=wx.ID_ANY, pos=wx.DefaultPosition,
                        size=wx.DefaultSize, style=wx.LC_REPORT|wx.LC_HRULES|wx.LC_VRULES|wx.LC_SORT_ASCENDING):
        wx.ListCtrl.__init__(self, parent, ID, pos, size, style)
        self.InsertColumn(0, "COB-ID")
        self.InsertColumn(1, "Type")
        self.InsertColumn(2, "Len")
        self.InsertColumn(3, "Data")
        self.InsertColumn(4, "Cycle [ms]")
        self.SetColumnWidth(0, 60)
        self.SetColumnWidth(1, 40)
        self.SetColumnWidth(2, 40)
        self.SetColumnWidth(3, 200)
        self.SetColumnWidth(4, 75)

    # either add messages to the listctrl or update the existing ones if 
    def Populate(self, msg_store):
        item=-1
        while 1:
            item = self.GetNextItem(item, wx.LIST_NEXT_ALL, wx.LIST_STATE_DONTCARE)
            if item == -1: break
            if self.GetItemText(item) not in msg_store:
                self.DeleteItem(item)

        for msg_id in msg_store:
            item = self.FindItem(-1, msg_id)
            msg = msg_store.get(msg_id)
            interval = randint(10,1000)
            # insert new messages
            if item == -1:
                item = self.InsertStringItem(sys.maxint, msg_id)
                self.SetStringItem(item, 1, 'std')
            # fill in other columns
            self.SetStringItem(item, 2, '%1d'%msg.LEN)
            self.SetStringItem(item, 3, ' '.join(['%02x'%d for d in msg.DATA[:msg.LEN]]))
            self.SetStringItem(item, 4, '%d'%interval)
#====================================================================
#====================================================================
if __name__=='__main__':
    msg=(0x180, 0, 8, range(1,9))
    can_send={}
    can_recv={}
    # just make up some simple messages for listctrl to display
    # send msgs
    for a in range(1,7):
        this_msg=list(msg)
        this_msg[0] += a
        can_send[hex(this_msg[0])] = CanMsg(*msg)
    # receive msgs
    for a in range(1,10):
        this_msg=list(msg)
        this_msg[0] += 0x100+a
        can_recv[hex(this_msg[0])] = CanMsg(*msg)

    app=wx.App(0)   # 0 arg stops stdout/stderr text box pop-up, messages go to console
    frame = EmulatorFrame(None, wx.ID_ANY, 'Listctrl flicker test')
    frame.Show(True)
    app.MainLoop()

Answer 1

Ok I think I finally have a workable (if partial) answer the flicker problem.

I found a number of people had success, mostly with image flickering, by enabling double buffering on the panel. So in the MessagesTab() class, after the wx.Panel init, I inserted the line;

self.SetDoubleBuffered(True)

This made the list control updates smooth but resizing the GUI or mousing over the listctrl column headers would make the contents flicker a lot or disappear entirely. Being Windows 7 the header highlights as per the OS theme when the mouse is on it. Since this seemed to be the cause my workaround was to add the wx.LC_NO_HEADER flag to the MessageList() style arg. So the listctrl has no header but nothing causes flicker or vanishing text now and I can replace it with some static text. Resizing is no problem either.

So maybe there's some problem with events generated on the column headers?

Answer 2

I would recommend using wxPython's Freeze and Thaw methods. Basically you Freeze the widget, update it and then you Thaw it.