[Python-bugs-list] Tkinter canvas blow-up: bbox(ALL) == None (PR#133)

[aa8vb@yahoo.com]

Full_Name: Randall Hopper
Version: 1.5.2
OS: IRIX 6.5
Submission from: ethyl-f.rtpfddi.epa.gov (134.67.65.11)


From: "Fredrik Lundh" <fredrik@pythonware.com>
Date: Tue, 2 Nov 1999 09:53:17 +0100
Subject: Re: Tkinter canvas blow-up:  bbox(ALL) == None

Randall Hopper <aa8vb@yahoo.com> wrote:
>      Apparently if the bounds of the items in a Tk canvas widget exceed
> MAXINT, bbox(ALL) returns None.  The attached Python script demonstrates
> this.
> 
>      Intuitively it seems like this is a bug since the contents of the
> canvas are maintained in floating point; integer bounds shouldn't be
> involved, should they?
> 
>      Is this a Tk bug or a Tkinter bug?

both.

Tkinter uses _getints instead of _getdoubles to
convert the bounding box to a tuple...

...but the reason you get None instead of an over-
flow error is that Tk returns an empty string in this
case (at least in 8.0.5).

-------------------------------------------------------------------------------
#!/usr/bin/env python                                                          

#                                                                              

#   canvas_test.py - Demonstrates a bug in Tkinter's Canvas widget             

#                    where bbox = None when the bbox exceeds signed MAXINT     

#                    (2^31 on most machines).                                  

                                                                               

from Tkinter import *                                                          

                                                                               

#                                                                              

# Create widgets                                                               

#                                                                              

root = Tk()                                                                    

canvas = Canvas( root, width = 300, height = 300 )                             

canvas.pack()                                                                  

canvas.create_rectangle( (-100,-100,100,100),                                  

                         outline = "#008000", fill="#800000", width = 3 )      

canvas.create_line( (-100,-100,100,100),                                       

                    fill="blue", width=3 )                                     

canvas.create_line( (-100,100,100,-100),                                       

                    fill="blue", width=3 )                                     

canvas.config( scrollregion = canvas.bbox( ALL ) )                             

                                                                               

#                                                                              

# Zoom the canvas until it's bounds get toasted because they exceed MAXINT     

#                                                                              

def TimerCB( canvas=canvas ):                                                  

  old = canvas.bbox( ALL )                                                     

  canvas.scale( ALL, 0.0, 0.0, 2.0, 2.0 )                                      

  new = canvas.bbox( ALL )                                                     

  print "Old = %s, New = %s" % ( old, new )                                    

  if new == None:                                                              

    raise SystemError, "canvas's bbox is toast (exceeds signed MAXINT)"        

  canvas.after( 300, TimerCB )                                                 

                                                                               

print "CANVAS ZOOM BLOW-UP TEST:\n"                                            

canvas.after( 1500, TimerCB )                                                  

root.mainloop()