How to stop pygame circles from overlapping?

Question

I am making a game in pygame, and I am trying to display 7 balloons (circles for now), with random colors, and a random x-axis. The colors are working, however, when trying to display the circles at a random x-axis, the circles usually overlap. How can I fix this issue?

Here's my code:

import pygame as pg
import random as r
import sys

pg.init()

def draw_balloons():
    global balloon_list
    global colors
    for i in range(7):
        balloon_x = r.randint(0, 500)
        balloon_color = (r.choice([0,255]), r.randint(0,255), r.choice([0,255]))
        balloon_list.append(balloon_x)
        colors.append(balloon_color)
        pg.draw.circle(screen, colors[i], (balloon_list[i], y), radius=30)

# Vars #
balloon_list = []
colors = []
x = 0
y = 250
velocity = 5
clock = pg.time.Clock()

screen = pg.display.set_mode((688 ,387)) # Size of the screen #
screen.fill('#ffffff')

caption = pg.display.set_caption("Remember") # Title of the window #


pg.display.flip() # Updating #

running = True # Game loop bool #

while running: # Game loop #
    clock.tick(60)
    for event in pg.event.get():
        if event.type == pg.QUIT:
            pg.quit()
            sys.exit()
        if event.type == pg.KEYDOWN:
            if event.key == pg.K_ESCAPE:
                pg.quit()
                sys.exit()

    draw_balloons()
    pg.display.update()

P.S: How can I make the circles in more of a balloon shape without using an image?

Answer 1

This following brute-force approach seems to work for the relatively small number of balloons. There's now a separate function called create_ballons() which does nothing by determine their positions and colors which is called outside the game loop. Given that, all draw_ballons() does now is draw them.

I say it's brute-force because it simply checks every new potential balloon x position against all of those already picked and ensures it's not too close to any of them.

One bug I noted about your draw_ballons() function is that it keeps appending more values to the two lists, but is only drawing the first seven — so eventually you'll run out of memory.

import pygame as pg
import random as r
import sys

MAX_ATTEMPTS = 1000
NUM_BALLOONS = 7
WIDTH, HEIGHT = 688, 387  # Screen size.
RADIUS = 30
DIAMETER = 2 * RADIUS

pg.init()

def create_balloons():
    global balloon_list
    global colors

    x_min, x_max = 0+RADIUS, WIDTH-RADIUS  # Constrain to be entirely on screen.
    max_balloons = (x_max-x_min) // DIAMETER  # Maximum that would fit.
    num_balloons = min(NUM_BALLOONS, max_balloons)  # No more than what could fit.

    balloon_list = []
    colors = []
    for _ in range(num_balloons):
        attempts = 0
        while (attempts := attempts+1) <= MAX_ATTEMPTS:
            candidate = r.randint(x_min, x_max)
            if all(abs(candidate-x) >= DIAMETER for x in balloon_list):  # No overlaps.
                break
        else:
            raise RuntimeError(f"No valid candiate after {attempts-1} attempts.")
        balloon_list.append(candidate)
        balloon_color = r.choice([0,255]), r.randint(0,255), r.choice([0,255])
        colors.append(balloon_color)

def draw_balloons(y):
    for i, x in enumerate(balloon_list):
        pg.draw.circle(screen, colors[i], (x, y), RADIUS)


# Vars #
balloon_list = []
colors = []
x = 0
y = 250
velocity = 5
clock = pg.time.Clock()

screen = pg.display.set_mode((WIDTH, HEIGHT)) # Size of the screen #
caption = pg.display.set_caption("Remember") # Title of the window #
create_balloons()

pg.display.flip() # Updating #

running = True # Game loop bool #

while running: # Game loop #
    clock.tick(60)
    for event in pg.event.get():
        if event.type == pg.QUIT:
            pg.quit()
            sys.exit()
        if event.type == pg.KEYDOWN:
            if event.key == pg.K_ESCAPE:
                pg.quit()
                sys.exit()

    draw_balloons(y)

    pg.display.update()

Here's a screenshot: