Dr Who Tunnel

# Dr Who
# @eigenbom
# Requires: pygame-zero

from math import sin, cos, pi
from random import uniform as u
import pygame

WIDTH, HEIGHT = 512, 512
center = WIDTH/2, HEIGHT/2
tunnel = center
time = 0

sign = lambda x: 1 if x > 0 else -1 if x < 0 else 0

def update(dt):
    global time, tunnel
    time += dt

def draw():
    global tunnel, center

    # rotate and zoom
    speedxor = 1.1 + 0.05 + 0.05*sin(time*0.33)
    rotxor = 5.5 + 1.0*sin(time*0.33)
    old_rect = screen.surface.get_rect()
    new_surface = pygame.transform.rotozoom(screen.surface, rotxor,speedxor)
    new_surface.set_alpha(200)
    new_rect = new_surface.get_rect()
    offx = old_rect.centerx - new_rect.width / 2
    offy = old_rect.centery - new_rect.height / 2
    screen.blit(new_surface, (offx,offy))

    # update tunnel center
    tunnel = center[0] + 10*sin(time), center[1] + 10*cos(time)

    # colour
    step = int(16 * (0.5 + 0.5*sin(time * 5)))
    col = 128 + step*8
    screen.draw.filled_circle(tunnel, 10, (col, col, col))
    screen.draw.filled_circle(tunnel, 5, (col/2,col/2,col/2))

    pulsor = sin(time*5) > 0.8
    twistor = sin(time*88.01)
    for i in range(4):
        x, y = 10*sin(-twistor*time*1.1 + i*pi/2), 10*cos(-twistor*time*1.1 + i*pi/2)
        if pulsor:
            colour = 0, 0, 0
        else:
            colour = [(255,0,0), (0, 255, 0), (0, 0, 255), (0, 128, 128)][i]
        screen.draw.filled_circle((tunnel[0] + x, tunnel[1] + y), int(5 + 2*sin(time)), colour)