Cfrgtkky

I wrote this piece of code for practicing, it moves my labels while the left mouse button pushed:

def motion(self, event):

    delta_x = event.x - self._drag_data["x"]

    delta_y = event.y - self._drag_data["y"]



    self.canvas.move(self._drag_data["item"], delta_x, delta_y)



    self._drag_data["x"] = event.x

    self._drag_data["y"] = event.y

Next i try to move the labels on a defined grid of lets say 5 pixels. So it is easier to "snap" the labels directly together.

How do i do this? Is there a way to move the label only every 5 pixels? So every 5 pixels the label jumps under the cursor again.

Here is the example i found where i extracted the function:

import tkinter as tk



class Example(tk.Frame):



    def __init__(self, parent):

        tk.Frame.__init__(self, parent)



        self.canvas = tk.Canvas(width=400, height=400)

        self.canvas.pack(fill="both", expand=True)



        self._drag_data = {"x": 0, "y": 0, "item": None}



        self._create_token((100, 100), "white")



        self.canvas.tag_bind("token", "<ButtonPress-1>", self.on_token_press)

        self.canvas.tag_bind("token", "<ButtonRelease-1>", self.on_token_release)

        self.canvas.tag_bind("token", "<B1-Motion>", self.on_token_motion)



    def _create_token(self, coord, color):

        (x,y) = coord

        self.canvas.create_oval(x-25, y-25, x+25, y+25, outline=color, fill=color, tags="token")



    def on_token_press(self, event):

        self._drag_data["item"] = self.canvas.find_closest(event.x, event.y)[0]

        self._drag_data["x"] = event.x

        self._drag_data["y"] = event.y



    def on_token_release(self, event):

        self._drag_data["item"] = None

        self._drag_data["x"] = 0

        self._drag_data["y"] = 0



    def on_token_motion(self, event):

        delta_x = event.x - self._drag_data["x"]

        delta_y = event.y - self._drag_data["y"]

        self.canvas.move(self._drag_data["item"], delta_x, delta_y)

        self._drag_data["x"] = event.x

        self._drag_data["y"] = event.y



if __name__ == "__main__":

    root = tk.Tk()

    Example(root).pack(fill="both", expand=True)

    root.mainloop()

Here we set deltas of x and y to 5 and then check whether mouse position is behind/under our item and if it is we multiply x or y it by -1 to make delta negative so our item will move in direction of our mouse.

def motion(self, event):

    delta_x = 0

    delta_y = 0

    step = 5



    if abs(event.x - self._drag_data["x"]) >= step:

        delta_x = step

    if abs(event.y - self._drag_data["y"]) >= step:

        delta_y = step



    if event.x < self._drag_data["x"]:

        delta_x *= -1

    if event.y < self._drag_data["y"]:

        delta_y *= -1



    self.canvas.move(self._drag_data["item"], delta_x, delta_y)



    if delta_x != 0:

        self._drag_data["x"] = event.x

    if delta_y != 0:

        self._drag_data["y"] = event.y

You can simply round the delta_x and delta_y to the closest multiple of the step size:

def on_token_motion(self, event):

    step = 20



    # Calculate drag distance

    delta_x = event.x - self._drag_data["x"]

    delta_y = event.y - self._drag_data["y"]



    # Round to nearest multiple of step size

    delta_x = int(step * round(float(delta_x)/step))

    delta_y = int(step * round(float(delta_y)/step))



    # Move the object

    self.canvas.move(self._drag_data["item"], delta_x, delta_y)



    # Update _drag_data to the new position

    self._drag_data["x"] = self._drag_data["x"] + delta_x

    self._drag_data["y"] = self._drag_data["y"] + delta_y

Note that I also changed the _drag_data update. The new position of the object is not equal to event.x anymore, since we snap to the grid. Therefore, we must update it as self._drag_data["x"] + delta_x, which is the old position plus the amount moved.