How to make ball stay within frame

[nathanael]

I want to be able to bounce the ball on the screen but when I run the code the ball moves of frame. I have attached a file of the code down below. Here's the code I have so far:

import time
import random
from graphics import *
def main():
      window_width=600
    window_length=700
    dx= int(1)
    dy= int(1)
    win= GraphWin("shapes", window_width, window_length)
    center= Point(dx,dy)
    circ= Circle(center, 30)
    circ.setFill('red')
    circ.draw(win)
    for i in range(100):
          
        dx1=random.randint(1,155)
        dy2=random.randint(1,155)
        dx+=dx1
        dy+=dy2
        if dx > window_width or dx <0:
           dx =1
        if dy > window_length or dy<0:
           dy=1
        circ.move(dx,dy)
        time.sleep(3)

buran write Nov-15-2025, 07:23 AM:
Please, use proper tags when post code, traceback, output, etc.
See BBcode help for more info.

[SledgeNE]

I think the main issue is you're updating dx and dy as positions, but then you're also using them as movement speeds. So the ball basically keeps jumping off screen because the random values get added to its coords every loop. For bouncing, you want to keep position and velocity separate.

So here's an example that actually keeps the ball inside the window:

from graphics import *
import time

def main():
    window_width = 600
    window_height = 700

    win = GraphWin("shapes", window_width, window_height)

    # starting position
    x = 100
    y = 100

    # velocity (keeps ball moving slowly)
    vx = 3
    vy = 3

    radius = 30
    circ = Circle(Point(x, y), radius)
    circ.setFill("red")
    circ.draw(win)

    while True:
        # bounce logic
        if x - radius <= 0 or x + radius >= window_width:
            vx = -vx
        if y - radius <= 0 or y + radius >= window_height:
            vy = -vy

        # update position
        x += vx
        y += vy

        circ.move(vx, vy)
        time.sleep(0.01)

main()

[deanhystad]

What you are trying to do is difficult. The only way to "move" a circle is to use the move() command, which moves relative from the current position. To ensure that the circle remains inside the window you need to bound the "new" position and compute the move from the current position to the new position.

import time
import random
from graphics import Circle, GraphWin, Point


def main():
    window_width = 600
    window_height = 700
    win = GraphWin("shapes", window_width, window_height)
    x = window_width // 2
    y = window_height // 2
    circ = Circle(Point(x, y), 30)
    circ.setFill('red')
    circ.draw(win)
    for i in range(100):
        # Compute new x and y positions that stay inside the window.
        new_x = min(window_width, max(1, x + random.randint(-75, 75)))
        new_y = min(window_height, max(1, y + random.randint(-75, 75)))
        # Move from old x, y to new x, y
        circ.move(new_x - x, new_y - y)
        # Update the x, y
        x = new_x
        y = new_y
        time.sleep(0.25)

It would be nice if the Circle class had a way to move the circle to a specific location. A beauty of python is it is easy to add new features to existing code. In the code below I add a moveTo method to the Circle class by subclassing. MyCircle can do everything Circle can do. In addition it has a moveTo(x, y) method and properties for getting the x and y coordinates of the circle center.

import time
from random import randint
from graphics import Circle, GraphWin, Point


class MyCircle(Circle):
    """Circle with additional features."""
    @property
    def x(self):
        return self.getCenter().getX()

    @property
    def y(self):
        return self.getCenter().getY()

    def moveTo(self, x, y):
        dx = x - self.x
        dy = y - self.y
        self.move(dx, dy)


def clip(value, vmin, vmax):
    """Clip value to be in range vmin..vmax."""
    return max(vmin, min(vmax, value))


def main():
    window_width = 600
    window_height = 700
    win = GraphWin("shapes", window_width, window_height)
    circles = []
    for color in ('black', 'red', 'green', 'blue', 'yellow'):
        circle = MyCircle(
            Point(randint(0, window_width), randint(0, window_height)),
            30
        )
        circle.setFill(color)
        circle.draw(win)
        circles.append(circle)
    for i in range(100):
        for c in circles:
            c.moveTo(
                clip(c.x + randint(-75, 75), 0, window_width),
                clip(c.y + randint(-75, 75), 0, window_height)
            )
        time.sleep(0.25)


main()

The new features make it so easy to write your program that I had to add 4 more circles.