Pygame: How to make two objects stop moving once they collide

Question

I'm attempting to make a simulation by generating particles (mainly circles) in pygame. One objective is to have the particle move randomly on the screen and once they collide, they should stick to each other and stay in their fixed position. I created a class called Particle which takes the following attributes: Particles(pos_x, pos_y, size, colour, screen). Then I generate a list of these particles on the screen so that they move randomly. However, I'm having a hard time conceptualizing how to loop through every particle and check if the distance between their respective x coordinates is less than 2*radius. (Example: if the radius of a particle is 5pixels, then particle_a(4, 8) would collide with particle_b(6, 8).

How would I go about checking each particle to see if they collide with each other? looping through a list of particles and then checking with a copy of that list but I'm not sure I'm going about this the right way. I can use all the help I can get. I'm still a beginner so I'd appreciate any help.

import sys
import pygame
import random
from dla_settings import Settings
from particles import Particles

PARTICLE_SIZE = 5
PARTICLE_COLOUR = (random.choice((200, 240)), 100, 0)


def dla_simulation():
    dla_settings = Settings()
    pygame.init()
    screen = pygame.display.set_mode((dla_settings.screen_width, dla_settings.screen_height))
    pygame.display.set_caption("DLA")

    screen.fill((10, 10, 10))
    pygame.display.update()

    main_particle = Particles(dla_settings.screen_width // 2,
                                dla_settings.screen_height // 2,
                                PARTICLE_SIZE,
                                PARTICLE_COLOUR,
                                screen)

    particles = []

    for particle in range(20):
        x = random.randint(400, 500)
        y = random.randint(400, 500)
        particle = Particles(x,
                                y,
                                PARTICLE_SIZE,
                                PARTICLE_COLOUR,
                                screen)
        particles.append(particle)
        particles_copy = particles.copy()
        print(particles_copy)


    # Start the main loop for the game.
    while True:
        # Watch for keyboard and mouse events.
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                sys.exit()

        screen.fill((10, 10, 10))
        main_particle.draw_particle()

        for particle in particles:
            particle.draw_particle()
            particle.random_move()
            for particle_copy in particles_copy:
                if particle.pos_x - particle_copy < 2:
                    particle.position_locked()

        # Update screen
        pygame.display.flip()


dla_simulation()

score 2 · Accepted Answer · answered May 28 '20 at 15:43

You have to compute and evaluate the distance from each particle to each other particle.

Use 2 nested loops. Each loop iterates through the particles. If the

for particle_a in particles:
    for particle_b in particles:

If particle_a and particle_b is the same, then continue the inner loop without doing anything:

if particle_a == particle_b:
    continue

Compute the Euclidean distance between the particles by math.sqrt(dx*dx + dy*dy) or hypot(dx, dy):

dx = particle_a.pos_x - particle_b.pos_x
dy = particle_a.pos_y - particle_b.pos_y
distance = math.sqrt(dx*dx + dy*dy)

Stop both particles, if the distance is below or equal 2*radius:

if distance <= 2*radius:
    particle_a.position_locked()
    particle_b.position_locked()

Algorithm

import math

for particle_a in particles:
    for particle_b in particles:
        if particle_a == particle_b:
            continue

        dx = particle_a.pos_x - particle_b.pos_x
        dy = particle_a.pos_y - particle_b.pos_y
        distance = math.sqrt(dx*dx + dy*dy)

        if distance <= 2*radius:
            particle_a.position_locked()
            particle_b.position_locked()

Pygame: How to make two objects stop moving once they collide

1 Answers1