getMouse tracking in Python using Zelle graphics.py

Question

I am new to Python. I need to write a program to move my ball or circle when I click the mouse. How do I achieve this? I have the below code that I got started with:

from graphics import *
import time

def MouseTracker():

win = GraphWin("MyWindow", 500, 500)
win.setBackground("blue")
cir = Circle(Point(250,250) ,20)
cir.setFill("red")
cir.draw(win)

while(win.getMouse() != None):
    xincr = 0
    yincr = 0
for i in range(7):
    cir.move(xincr, yincr)
    time.sleep(.2)
win.getMouse()

Answer 1

Assuming you are not bound to some specific tools or implementation, you may find matplotlib useful. You can plot a circle onto the drawing area using a circle patch (http://matplotlib.org/api/patches_api.html) and then move it around when there is mouse-click in the graph axes. You will need to connect to the event-click listener and define a callback function which handles the drawing update - see http://matplotlib.org/users/event_handling.html for examples of how to do this. You can get the coordinates of the mouse press using the xdata and ydata methods.

This worked for me in python 2.7:

import matplotlib.pyplot as plt
from matplotlib.patches import Circle

fig = plt.figure()
ax = fig.add_subplot(111)
circ = Circle((0.5,0.5), 0.1)
ax.add_patch(circ)

def update_circle(event):
    ax.cla()
    circ = Circle((event.xdata, event.ydata), 0.1)
    ax.add_patch(circ)
    fig.canvas.draw()

fig.canvas.mpl_connect('button_press_event', update_circle)
plt.show()

Answer 2

Assuming you want to stick with the graphics package you started with, you can do it but you're missing code to save the mouse position and compare it to the circle's center position:

from graphics import *

WIDTH, HEIGHT = 500, 500
POSITION = Point(250, 250)
RADIUS = 20
STEPS = 7

def MouseTracker(window, shape):
    while True:
        position = window.getMouse()

        if position != None:  # in case we want to use checkMouse() later
            center = shape.getCenter()
            xincr = (position.getX() - center.getX()) / STEPS
            yincr = (position.getY() - center.getY()) / STEPS
            for _ in range(STEPS):
                shape.move(xincr, yincr)

win = GraphWin("MyWindow", WIDTH, HEIGHT)
win.setBackground("blue")

cir = Circle(POSITION, RADIUS)
cir.setFill("red")
cir.draw(win)

MouseTracker(win, cir)

You will need to close the window to break out of the tracking loop -- in a real program you'd handle this as part of the design (i.e. some user action causes a break in the while True: loop.)