TkInter: drawing on wrong positions

问题

I load a picture on the Canvas. It is a large picture so I need to scroll vertically and horizontally to be able to see it. I also let the user to drawn random curves/lines using the mouse pointer on the image.

Everything is ok except that when I scroll horizontally or vertically then I try to draw I see the curves are not drawn where the mouse points to but in an other place. How can I resolve this problem ?

Here is my code:

import PIL.Image
import PIL.ImageTk
from Tkinter import *    
import numpy as np
import cv2   

class ExampleApp(Frame):
   def __init__(self,master):
        Frame.__init__(self,master=None)
        self.x = self.y = 0
        self.imcv=None
        self.canvas=Canvas(self,width=600,height=600)
        self.b1="up"
        self.liste=[]
        self.xold=None
        self.yold=None

   def dessiner(self):
       # Load the imge and allow user to scroll it if it is large.
       self.canvas.bind("<Motion>",self.motion)
       self.canvas.bind("<ButtonPress-1>",self.b1down)
       self.canvas.bind("<ButtonRelease-1>",self.b1up)
       self.sbarv=Scrollbar(self,orient=VERTICAL)
       self.sbarh=Scrollbar(self,orient=HORIZONTAL)
       self.sbarv.config(command=self.canvas.yview)
       self.sbarh.config(command=self.canvas.xview)

       self.canvas.config(yscrollcommand=self.sbarv.set)
       self.canvas.config(xscrollcommand=self.sbarh.set)

       self.canvas.grid(row=0,column=0,sticky=N+S+E+W)
       self.sbarv.grid(row=0,column=1,stick=N+S)
       self.sbarh.grid(row=1,column=0,sticky=E+W)
       self.im = PIL.Image.open("image.jpg")
       self.widt,self.heigt=self.im.size
       self.canvas.config(scrollregion=(0,0,self.widt,self.heigt))
       self.tk_im = PIL.ImageTk.PhotoImage(self.im)
       self.canvas.create_image(0,0,anchor="nw",image=self.tk_im)   


   def b1up(self,event):
       self.b1="up"
   def b1down(self,event):
       self.b1="down"
       self.xold=None
       self.yold=None
       self.liste.append((self.xold,self.yold))
   def motion(self,event):
       if self.b1=="down":
           if self.xold is not None and self.yold is not None:
               event.widget.create_line(self.xold,self.yold,event.x,event.y,fill="red",width=3,smooth=TRUE)
           self.xold=event.x
           self.yold=event.y
           self.liste.append((self.xold,self.yold))


if __name__ == "__main__":
    root=Tk()
    app = ExampleApp(root)
    app.pack()
    app.dessiner()
    root.mainloop()

If you want to see my problem then you can download this large image and name it image.jpg and run the code.

May be the solution resides in using canvasx and canvasy but I do not know how.

Thank you in advance

回答1:

Coordinates in the event object are in the window coordinate system. You need to convert them to the canvas coordinate system. Tkinter has two methods for that: canvasx and canvasy.

回答2:

I resolved the problem by changing these lines:

event.widget.create_line(self.xold,self.yold,event.x,event.y,fill="red",width=3,smooth=TRUE)

and:

self.xold=event.x
self.yold=event.y

to:

event.widget.create_line(self.xold,self.yold,self.canvas.canvasx(event.x),self.canvas.canvasy(event.y),fill="red",width=3,smooth=TRUE)

and:

self.xold=self.canvas.canvasx(event.x)
self.yold=self.canvas.canvasy(event.y)

来源：https://stackoverflow.com/questions/30256715/tkinter-drawing-on-wrong-positions

标签

python

python-2.7

tkinter