# Uses built-in neopixel module

from machine import Pin
import neopixel
import time

PIXEL_PIN = 15
NUM_PIXELS = 16

np = neopixel.NeoPixel(Pin(PIXEL_PIN, Pin.OUT), NUM_PIXELS)

# --- helpers -------------------------------------------------------------

def hsv_to_rgb(h, s=255, v=255):
    # h: 0..65535, s/v: 0..255
    h = h % 65536
    region = (h * 6) // 65536
    f = (h * 6) - region * 65536

    p = (v * (255 - s)) // 255
    q = (v * (255 - (s * f // 65535))) // 255
    t = (v * (255 - (s * (65535 - f) // 65535))) // 255

    if region == 0:
        return v, t, p
    if region == 1:
        return q, v, p
    if region == 2:
        return p, v, t
    if region == 3:
        return p, q, v
    if region == 4:
        return t, p, v
    return v, p, q

def gamma8(x):
    return int(((x / 255) ** 2.8) * 255 + 0.5)

def gamma_rgb(r, g, b):
    return gamma8(r), gamma8(g), gamma8(b)

# --- main loop -----------------------------------------------------------

hue = 0  # 0..65535

while True:
    for i in range(NUM_PIXELS):
        h = hue + i * (65535 // NUM_PIXELS)
        r, g, b = hsv_to_rgb(h)
        np[i] = gamma_rgb(r, g, b)

    np.write()
    hue = (hue + 512) & 0xFFFF   # animation speed
    time.sleep_ms(20)