Matrix effect for Pico Scroll Pack board

matrix.py

# Simple Matrix style effect for Pico Scroll Pack board from Pimoroni and MicroPython on Raspbery Pi Pico

# see: https://twitter.com/horcicaa/status/1439327623843307523

# doc: https://shop.pimoroni.com/products/pico-scroll-pack
#      https://github.com/pimoroni/pimoroni-pico/tree/main/micropython/modules/pico_scroll

import time
import random
import picoscroll as scroll

# --- config ---

# Initial brightness for new pixel
brightness = 30

# How much pixel should fade on next line
fade = 0.8

# Probability of new pixel ( 1 : n )
probability = 5

# --------------

scroll.init()

W = scroll.get_width()
H = scroll.get_height()

buffer = bytearray(0 for j in range(W*H))

# Calc. index of pixel in buffer by x and y position
def n(x, y):
    return y * W + x

while True:
    
    # Shift rows one row down
    for x in range(W-1, 0, -1):
        for y in range(0, H):
            buffer[n(x,y)] = buffer[n(x-1, y)]
        
    # Calculate new row on top    
    for i in range(0, H):
        buffer[n(0, i)] = int(buffer[n(1, i)] * fade) 

    # Add point 
    if random.randint(0, probability - 1) == 0:
        buffer[n(0, random.randint(0, H-1))] = brightness

    # Refresh
    scroll.set_pixels(buffer)
    scroll.update()
    
    time.sleep(0.04)