Draw trajectory from data stream in real-time using wxpython - python-2.7

Question

I want to use wxpython to show the trajectory of a random walk in real-time. However, the panel is updated only once at the end showing the entire random walk instead of updating step by step and showing the time course.
My first idea was to use wx.ClientDC().DrawPoint() but the result was as described above where I did not see single points being drawn but only the final result was shown.
So instead I thought about using wx.MemoryDC to draw the trajectory to a bitmap stored in memory and then use wx.ClientDC.DrawBitmap() to copy the buffered image to the screen at set time intervals in case flipping the image was the bottleneck. The result is still the same so I am hoping for you help.
The purpose of this exercise is to replace the random walk with positional data coming from an eye tracker with a frame rate of 1000 Hz and I would like to be able to visualize the trajectory in as close to real-time as possible (the monitor's frame rate is 120Hz).
This is my code (most of it comes from here):
import wx
import random
import time
from time import asctime
#-------------------------------------------------------------------
def jmtime():
return '[' + asctime()[11:19] + '] '
#-------------------------------------------------------------------
class MyDrawingArea(wx.Window):
def __init__(self, parent, id):
sty = wx.NO_BORDER
wx.Window.__init__(self, parent, id, style=sty)
self.parent = parent
self.SetBackgroundColour(wx.WHITE)
self.SetCursor(wx.CROSS_CURSOR)
# Some initalisation, just to reminds the user that a variable
# called self.BufferBmp exists. See self.OnSize().
self.BufferBmp = None
wx.EVT_SIZE(self, self.OnSize)
wx.EVT_PAINT(self, self.OnPaint)
wx.EVT_LEFT_DOWN(self,self.OnClick)
def OnSize(self, event):
print jmtime() + 'OnSize in MyDrawingArea'
# Get the size of the drawing area in pixels.
self.wi, self.he = self.GetSizeTuple()
# Create BufferBmp and set the same size as the drawing area.
self.BufferBmp = wx.EmptyBitmap(self.wi, self.he)
memdc = wx.MemoryDC()
memdc.SelectObject(self.BufferBmp)
# Drawing job
ret = self.DoSomeDrawing(memdc)
if not ret: #error
self.BufferBmp = None
wx.MessageBox('Error in drawing', 'CommentedDrawing', wx.OK | wx.ICON_EXCLAMATION)
def OnPaint(self, event):
print jmtime() + 'OnPaint in MyDrawingArea'
dc = wx.PaintDC(self)
dc.BeginDrawing()
if self.BufferBmp != None:
print jmtime() + '...drawing'
dc.DrawBitmap(self.BufferBmp, 0, 0, True)
else:
print jmtime() + '...nothing to draw'
dc.EndDrawing()
def OnClick(self,event):
pos = event.GetPosition()
dc = wx.ClientDC(self)
dc.SetPen(wx.Pen(wx.BLACK,1,wx.SOLID))
dcwi, dche = dc.GetSizeTuple()
x = pos.x
y = pos.y
time_start = time.time()
memdc = wx.MemoryDC()
memdc.SelectObject(self.BufferBmp)
memdc.SetPen(wx.Pen(wx.BLACK,1,wx.SOLID))
count = 1
runtime = 5
while (time.time() - time_start) < runtime:
x,y = random_walk(x,y,dcwi,dche)
memdc.DrawPoint(x,y)
if (time.time() - time_start) > count * runtime * 0.1:
print jmtime() + 'Random walk in MyDrawingArea'
count += 1
dc.BeginDrawing()
dc.DrawBitmap(self.BufferBmp, 0, 0, True)
dc.EndDrawing()
dc.BeginDrawing()
dc.DrawBitmap(self.BufferBmp, 0, 0, True)
dc.EndDrawing()
# End of def OnClick
def DoSomeDrawing(self, dc):
try:
print jmtime() + 'DoSomeDrawing in MyDrawingArea'
dc.BeginDrawing()
#~ raise OverflowError #for test
# Clear everything
dc.SetBrush(wx.Brush(wx.WHITE, wx.SOLID))
dc.Clear()
dc.EndDrawing()
return True
except:
return False
#-------------------------------------------------------------------
class MyPanel(wx.Panel):
def __init__(self, parent, id):
wx.Panel.__init__(self, parent, id, wx.DefaultPosition, wx.DefaultSize)
self.drawingarea = MyDrawingArea(self, -1)
self.SetAutoLayout(True)
gap = 30 #in pixels
lc = wx.LayoutConstraints()
lc.top.SameAs(self, wx.Top, gap)
lc.left.SameAs(self, wx.Left, gap)
lc.right.SameAs(self, wx.Width, gap)
lc.bottom.SameAs(self, wx.Bottom, gap)
self.drawingarea.SetConstraints(lc)
#-------------------------------------------------------------------
# Usual frame. Can be resized, maximized and minimized.
# The frame contains one panel.
class MyFrame(wx.Frame):
def __init__(self, parent, id):
wx.Frame.__init__(self, parent, id, 'CommentedDrawing', wx.Point(0, 0), wx.Size(500, 400))
self.panel = MyPanel(self, -1)
wx.EVT_CLOSE(self, self.OnCloseWindow)
def OnCloseWindow(self, event):
print jmtime() + 'OnCloseWindow in MyFrame'
self.Destroy()
#-------------------------------------------------------------------
class MyApp(wx.App):
def OnInit(self):
frame = MyFrame(None, -1)
frame.Show(True)
self.SetTopWindow(frame)
return True
#-------------------------------------------------------------------
def random_walk(x,y,sizex = 250, sizey = 200):
rn = random.randrange(0,2)
x_new = x + (1-rn) - rn
while x_new < 0 or x_new > sizex:
rn = random.randrange(0,2)
x_new = x + (1-rn) - rn
rn = random.randrange(0,2)
y_new = y + (1-rn) - rn
while y_new < 0 or y_new > sizex:
rn = random.randrange(0,2)
y_new = y + (1-rn) - rn
return x_new, y_new
# end of def random_walk
#-------------------------------------------------------------------
def main():
print 'main is running...'
app = MyApp(0)
app.MainLoop()
#-------------------------------------------------------------------
if __name__ == "__main__" :
main()
#eof-------------------------------------------------------------------

Answer 1

This is the solution I came up with. Instead of using dc.DrawBitmap() to copy the buffered image to the screen I used Update() and Refresh() to trigger a paint event. However, what I still don't understand is why I cannot use DrawBitmap() to accomplish the same.
The only difference is that OnPaint() uses PaintDC() and in OnClick() I use ClientDC().
Anyways, this is my current code for OnClick():
def OnClick(self,event):
pos = event.GetPosition()
x = pos.x
y = pos.y
time_start = time.time()
memdc = wx.MemoryDC()
memdc.SelectObject(self.BufferBmp)
dcwi, dche = memdc.GetSizeTuple()
memdc.SetPen(wx.Pen(wx.BLACK,1,wx.SOLID))
runtime = 10
while (time.time() - time_start) < runtime:
x,y = random_walk(x,y,dcwi,dche)
memdc.SelectObject(self.BufferBmp)
memdc.DrawPoint(x,y)
memdc.SelectObject(wx.NullBitmap)
self.Update()
self.Refresh()
print jmtime() + 'Random walk in MyDrawingArea done'