[Tutor] 1 or 2 Tkinter Canvas questions

[Gregor Lingl]

Hi!

The very interesting reply to the last
posting of Marilyn lets me hope, that
there are people reading and writing
here, who can answer the following questions:

Recently I wrote a simple Tkinter program
example which should draw a maximal rectangle
on a (resizable) Canvas. It goes essentially
like this:

from Tkinter import *

class RedRect(Tk):
   def __init__(self):
       Tk.__init__(self)
       self.title("RedRect")
       CvRedRect(self).pack(expand=1, fill="both")

class CvRedRect(Canvas):
   def __init__(self, root):
       Canvas.__init__(self, root, bg="white")
       self.bind("<Configure>", self.paint)
       self.r = self.create_rectangle(0,0,0,0, outline="red")
       self.txt1 = self.create_text(30,30,text="")
       self.txt2 = self.create_text(30,60,text="")
   def paint(self, event):
       w,h=event.width, event.height
       self.itemconfig(self.txt1, text=str(w))
       self.itemconfig(self.txt2, text=str(h))
       self.coords(self.r,2,2,w-3,h-3)

if __name__ == "__main__":
   RedRect().mainloop()   # Marilyn's idea, nice!

Now my questions:

(1) Why do I have to use in
       self.coords(self.r,2,2,w-3,h-3)
   the constant(s)  2 and 3? One would expect, that
   something like
       self.coords(self.r,0,0,w-1,h-1)
   or
       self.coords(self.r,0,0,w,h)
   would work. But no, these rectangles are outside
   the visible prtion of the canvas. Moreover: is
   there some property ("option") of canvas which
   represents this sort of "inset"?

   Shortly: why doesn't appear the whole Canvas on the
   screen?

(2) Why does apparently
       self.geometry("400x300+50+50")
   determine the size of the canvas packed into the
   Tk() - window and not the sizue of the Tk-window
   it*self*, which is 408*327 pixels?

Minor questions, maybe. But I find it annoying that I need
*experiment* with canvas and rectangle in order to get it as
wanted. I'd prefer to compute it over trial an error.

Thanks in advance

Gregor