Curtis Brownian Motion (WILL NEED PYGAME)

import pygame
import random

# Define some colors
BLACK = (0, 0, 0)
WHITE = (255, 255, 255)
GREEN = (0, 255, 0)
RED = (255, 0, 0)

# Defines variables for all particles
posx = [10,10,25,500] # origonal X axis
posy = [10,460,20,20] # origonal Y axis
speedx = [0,0,1,1] # speed for the X axis
speedy = [1,1,0,0] # speed for the Y axis
sizexy = [20,20,20,20] # size of each particle


# the block of code before is used to randomly generate information for starting positions (this would be used for the final sim)
"""
for i in range(2):
    posx.append(random.randint(10,690))
    posy.append(random.randint(10,490))
    speedx.append(1)
    speedy.append(1)
    sizexy.append(20)
"""

pygame.init()

# Set the width and height of the screen [width, height]
size = (700, 500)
screen = pygame.display.set_mode(size)

pygame.display.set_caption("Brownian Motion") #sets the name of the window

# This makes the program shutdown when the close button is clicked
done = False

# Used to manage how fast the screen updates
clock = pygame.time.Clock()

# -------- Main Program Loop -----------
while not done:
    # --- Main event loop
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            done = True

    # --- Game logic should go here

    #this changes the position of the box every tick by its speed
    for i in range(len(posx)):
        i -= 1
        posx[i] = posx[i] + speedx[i]
        posy[i] = posy[i] + speedy[i]
        i += 1

    #this is collision detection
    #this block is to bounce on the y axis, it checks if the two particles are on the same axis, then if they are close enough to be considered touching, if they are it reverses the y speed
    for i in range(len(posx)):
        for j in range(len(posx)):
            if i != j:
                if posx[i] == posx[j]:
                     if posy[i] - posy[j] < sizexy[i] and posy[i] - posy[j] > -1* sizexy[1] :
                            speedy[i] *= -1
    #this does the same as the last block but checks if in the same y axis and then changes the x axis if too close
    for i in range(len(posx)):
        for j in range(len(posx)):
            if i != j:
                if posy[i] == posy[j]:
                     if posx[i] - posx[j] < sizexy[i] and posx[i] - posx[j] > -1* sizexy[1] :
                            speedx[i] *= -1



    #this detects if the box is at a wall, and if it is it reverses its movement along that axis to bounce
    for i in range(len(posy)):
        i-=1
        if posy[i] > 500 - sizexy[i]:
            speedy[i] = speedy[i] * -1
        if posy[i] < 0:
            speedy[i] = speedy[i] * -1

        if posx[i] > 700 - sizexy[i]:
            speedx[i] = speedx[i] * -1
        if posx[i] < 0:
            speedx[i] = speedx[i] * -1
        i+=1


       # --- Drawing code should go here

    # First, clear the screen to black. Don't put other drawing commands
    # above this, or they will be erased with this command.
    screen.fill(BLACK) #background colour

    pygame.draw.rect(screen, WHITE, [posx[0], posy[0], sizexy[0],sizexy[0]])
    pygame.draw.rect(screen, RED, [posx[1], posy[1], sizexy[1],sizexy[1]])
    pygame.draw.rect(screen, GREEN, [posx[2], posy[2], sizexy[2],sizexy[2]]) #this draws each rectangle a different color and uses each particles statistics on where it should be
    pygame.draw.rect(screen, RED, [posx[3], posy[3], sizexy[3],sizexy[3]])

    #the below block is used to automatically go through all the lists and make that many squares in the correct positions, useful for masses of particles, but they are all the same color so you cant tell if collision is working
    """for i in range(len(posx)):
        i -=1
        pygame.draw.rect(screen, WHITE, [posx[i], posy[i], sizexy[i],sizexy[i]]) # this draws a rectangle on the screen, in white with the position of posx,posy and with sizex and sizy for its size
        i+=1
    """
    # --- Go ahead and update the screen with what we've drawn.
    pygame.display.flip() # this is nessacary for computor reasons reasons

    # --- Limit to 60 frames per second
    clock.tick(60)

# Close the window and quit.
# If you forget this line, the program will 'hang'
# on exit if running from IDLE.
pygame.quit()