[Tutor] how can a value be retrieved from an event loop?

[Alan Gauld]

On 16/11/2023 13:45, Alan Gauld via Tutor wrote:

> OK, I took your code and tweaked it to do what I think you want.
> Note that you now set the initial angle by passing it to the
> constructor call.

I was sufficiently intrigued by this that I took another pass
and added a label to demonstrate how it could be used and
did the display conversion to degrees too. I hope that it's
helpful. I also tidied up the code some more.

import tkinter as tk
import math


class KNOB(tk.Canvas):
     def __init__(
         self,
         parent,
         size=100,
         angle=0,
         string_var = None
     ):
         super().__init__(parent, width=size, height=size)

         self.size = size
         self.color1 = "#007DC8"
         self.color2 = "#98D2D2"
         self.angle = angle % (2 * math.pi) # keep within 0-2pi
         self.str_var = string_var

         self.border = self.create_oval(
             0.1 * size,
             0.1 * size,
             0.9 * size,
             0.9 * size,
             outline=self.color1,
             width=3,
             fill=self.color2,
         )
         self.dot = None   # make a "dot" for first draw_dot to remove!
         self.draw_dot()

         self.bind("<Button-3>", self.turn_clockwise)
         self.bind("<Button-1>", self.turn_counterwise)

     def draw_dot(self):
         self.delete(self.dot)
         centerX = 0.5 * self.size + (0.25 * self.size *
math.sin(self.angle))
         centerY = 0.5 * self.size - (0.25 * self.size *
math.cos(self.angle))
         self.dot = self.create_oval(
             (centerX - 0.05 * self.size),
             (centerY - 0.05 * self.size),
             (centerX + 0.05 * self.size),
             (centerY + 0.05 * self.size),
             outline=self.color1,
             width=3,
         )
         if self.str_var:
             self.str_var.set("%5.2f deg." % math.degrees(self.angle))

     def turn_clockwise(self, event):
         self.set_angle(self.angle + 0.1)
         self.draw_dot()


     def turn_counterwise(self, event):
         self.set_angle(self.angle - 0.1)
         self.draw_dot()

     def set_angle(self,angle):
         self.angle = angle % (2*math.pi)  # keep within 0-2pi range

if __name__ == "__main__":
     root = tk.Tk()
     root.title("Knob test")
     knob_angle = tk.StringVar()
     knob_angle.set("0")

     knob = KNOB(root, angle=15, string_var = knob_angle)
     knob.pack(padx=20, pady=20)
     lbl = tk.Label(root, textvariable=knob_angle)
     lbl.pack()

     root.mainloop()

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos