[Tutor] Canvas Widget

[Danny Yoo]

On Mon, 14 Apr 2003, Diego Prestes wrote:

>      Im trying to use canvas in tkinter but when I put the widget it
> always stay in the top of the program. I try to make a frame with the
> side=TOP to put the buttons of the toolbar but it stay in bottom.
>
>      Someone know if I can change the side of the canvas?

Hi Diego,

Tkinter's default "packing" layout system is a little bit weird at first,
so let's go through a small example; it might help clear things up.


If you want to make something like:

+-----------------+---------+
|                 |         |
|                 | Button1 |
|                 |---------+
|    Canvas       |         |
|                 | Button2 |
|                 |---------+
|                 |         |
|                 | Button3 |
+-----------------+---------+



To construct something like this, we can think of it as two pieces, a
canvas on the left hand side,

+-----------------+
|                 |
|                 |
|    Canvas       |
|                 |
|                 |
|                 |
|                 |
|                 |
+-----------------+


plus a frame of buttons on the right hand side:

+---------+
|         |
| Button1 |
|---------+
|         |
| Button2 |
|---------+
|         |
| Button3 |
+---------+


Here's some example Tkinter code that constructs a window like this:

###
>>> import Tkinter
>>> root = Tkinter.Tk()
>>> canvas = Tkinter.Canvas(root)
>>> canvas.pack(side=Tkinter.LEFT)
>>> button_frame = Tkinter.Frame(root)
>>> button_frame.pack(side=Tkinter.RIGHT)
>>> b1, b2, b3 = (Tkinter.Button(text="Button1"),
...               Tkinter.Button(text="Button2"),
...               Tkinter.Button(text="Button3"))
>>> b1.pack(side=Tkinter.TOP)
>>> b2.pack(side=Tkinter.TOP)
>>> b3.pack(side=Tkinter.TOP)
###


The order of packing can matter: you may want to experiment with your
interactive interpreter to see what happens if we pack the button_frame to
the LEFT first, and then the canvas.



> and other question. Someone know how can I create a rectangle, for
> example, using the mouse?

You may want to look at Fredrik's tutorial on Tkinter:

   http://www.pythonware.com/library/tkinter/introduction/


In particular, if we look at the Canvas documentation:

   http://www.pythonware.com/library/tkinter/introduction/x2102-methods.htm

we can see a method called "create_rectangle" that takes a "bounding box".
Here's an example call to create_rectangle:


###
>>> canvas.create_rectangle(((10, 10), (20, 20)))
1
###


A gloriously puny rectangle should show up on the upper left hand corner
of the canvas.  *grin*


To do drawing with a mouse, you may need to read a little bit about "event
handling".  Here's a link to the Events section of Tkinter tutorial:

 http://www.pythonware.com/library/tkinter/introduction/events-and-bindings.htm


Please feel free to ask questions on Tutor; we'll be happy to help clear
up the confusing parts.  Good luck!