#! /usr/bin/env python
 
# Plot random pixels on the screen.
 
import pygame
import random

def StartPunkt():
  x = MaxX2  #random.randint(0,200)-100 + MaxX2
  return x,0

def Angekommen(x, y, maxX, maxY):
  if (y >= maxY-1) or (x <= 0) or (x > maxX):
    return True  
  for i in range(x-1,x+2):
    for j in range(y,y+2):
      rgb = screen.get_at((i, j))[:3]#  nur rgb ohne Alpha als tupel
      if rgb[0]+rgb[1]+rgb[2] == 255:
        return True
  return False
  
def NeueKoordinatenBestimmen(x, y):
  x = x + random.randint(0,4)-2
  y = y + random.randint(0,2)   # nur nach oben
  return x,y


MaxX = 640
MaxX2 = MaxX // 2
MaxY = 400
white = [255, 255, 255]
green = [0, 255, 0]
chr_speed = input("Geschwindigkeit [500]: ")
if chr_speed == "":
    speed = 500
else:
    speed = int(chr_speed)


screen = pygame.display.set_mode((MaxX, MaxY))
screen.fill(white)
pygame.display.update()
clock = pygame.time.Clock()
 
running = True
while running:
    x,y = StartPunkt()
#    print(x,y,Angekommen(x,y,MaxX,MaxY))
    while not Angekommen(x,y,MaxX,MaxY):
      xNeu,yNeu = NeueKoordinatenBestimmen(x,y)
#      print("Neu:",x,y,Angekommen(x,y,MaxX,MaxY))
      if (x < 0) or (x >= MaxX-1):
        xNeu,yNeu = StartPunkt()

      for event in pygame.event.get():
         if event.type == pygame.QUIT:   # warten auf beliebige Taste
             running = False

      x,y = xNeu,yNeu

    screen.set_at((x, y), green)
#    pygame.draw.rect(screen, green, pygame.Rect(MaxX2-10,0,20,10))
    pygame.display.flip()
    clock.tick(speed)
    if y < 1:
      while True:
        for event in pygame.event.get():
            exit()

pygame.quit()