accrete falling pixels

accrete.py

# public domain
import pygame
from random import randint

width = 400
height = 400
screen = pygame.display.set_mode((width, height))

color = (255,255,255)

def clampWidth(x):
    return max(min(x,width-1),0)

neighbors = ( (0,1), (1,1), (-1,1), (-1,0), (1,0) )    
    
def haveNeighbor(x,y):
    if y >= height-1:
        return True
    for n in neighbors:
        if screen.get_at((clampWidth(x+n[0]),y+n[1])) == color:
            return True
    return False
             

while True:
    if pygame.QUIT in (event.type for event in pygame.event.get()):
        break

    x = randint(width//3,2*width//3) #randint(0,width-1)
    y = 0
    
    while True:
        if haveNeighbor(x,y):
            screen.set_at((x,y),color)
            pygame.display.flip()
            break
        x = clampWidth( x + randint(-1,1) )
        y += 1