Canvas with scrollbars - how to get correct canvas coordinate when the scroll bars have moved?

[PhilC]

Hi Folks,

I'm trying to click on a canvas to draw a line. The canvas has scroll
bars. All is well until I move the scrollbars. This naturally because
the relationship between my screen click and canvas event.x, event.y
has changed.

I need something that will add the proportional amount the scroll bar
has moved to the mouse click position. I see the terms canvasx and
canvasy but they appear to be used for converting screen position to
canvas position.

A pointer in the right direction would be appreciated.

Thanks

PhilC

 

[Eric Brunel]

Hi Folks,

I'm trying to click on a canvas to draw a line. The canvas has scroll
bars. All is well until I move the scrollbars. This naturally because
the relationship between my screen click and canvas event.x, event.y
has changed.

I need something that will add the proportional amount the scroll bar
has moved to the mouse click position. I see the terms canvasx and
canvasy but they appear to be used for converting screen position to
canvas position.

Either I do not understand your question, or canvasx and canvasy are exactly
what you're looking for:

------------------------------------------------------------
from Tkinter import *

root = Tk()
root.grid_rowconfigure(0, weight=1)
root.grid_columnconfigure(0, weight=1)
cnv = Canvas(root, scrollregion=(0, 0, 1000, 1000))
cnv.grid(row=0, column=0, sticky='nswe')
hs = Scrollbar(root, orient=HORIZONTAL, command=cnv.xview)
hs.grid(row=1, column=0, sticky='we')
vs = Scrollbar(root, orient=VERTICAL, command=cnv.yview)
vs.grid(row=0, column=1, sticky='ns')
cnv.configure(xscrollcommand=hs.set, yscrollcommand=vs.set)

def click(evt):
x, y = cnv.canvasx(evt.x), cnv.canvasy(evt.y)
cnv.create_oval(x - 5, y - 5, x + 5, y + 5)

cnv.bind('<1>', click)

root.mainloop()
------------------------------------------------------------

"Canvas position" is the position in the drawable zone for the canvas,
considering the scroll-region. Isn't it what you want?

HTH

 

[PhilC]

Thanks Eric,

I thought so too

Re looked at my script and I had an error further down. Corrected that
and the scrolling all works. Part of my inexperience is not knowing
where to look for the errors. I'm sure that comes with practice.

Many thanks for taking the time to answer me it is much appreciated.

Regards

Phil