Stop the light game on a Raspberry Pi Pico

// Stop the light: an arcade timing game on a ring of 16 NeoPixels and a
// Raspberry Pi Pico. A red light runs round the ring. Press the button just
// as it lands on the green LED.
//
//   LED ring   DIN -> GP22, 5V -> VBUS, GND -> GND (16 WS2812B LEDs)
//   button     GP14 and GND (INPUT_PULLUP: a press reads LOW)
//   piezo      GP7 and GND
//
// Catch it and you go up a level: the light runs faster. Miss and the game is
// over; the ring shows where the light stopped and how far off you were. The
// best level is shown on the Serial Monitor. While no game is running the
// ring spins a rainbow; press the button to start.
//
// # Where is the light?
//
// The light's position is worked out from the time, not counted step by
// step: (millis since the level started) / (ms per LED), round the ring.
// That keeps the speed exact however long the rest of loop() takes, and the
// moment the button goes down the sketch knows exactly which LED was lit.

#include <Adafruit_NeoPixel.h>

const uint8_t RING_PIN = 22;
const uint8_t BUTTON = 14;
const uint8_t PIEZO = 7;
const uint8_t LEDS = 16;
const uint8_t TARGET = 0;  // the green LED
const uint8_t START = 8;   // the light starts opposite it

Adafruit_NeoPixel ring(LEDS, RING_PIN, NEO_GRB + NEO_KHZ800);

uint8_t level = 1;
uint8_t best = 0;
bool playing = false;
unsigned long levelStarted = 0;
bool lastButton = HIGH;
unsigned long buttonAt = 0;

// Each level the light is 15% faster, never quicker than 25 ms an LED.
unsigned long stepMs() {
  unsigned long ms = 150;
  for (uint8_t i = 1; i < level; i++) ms = ms * 85 / 100;
  return ms < 25 ? 25 : ms;
}

uint8_t lightAt(unsigned long now) {
  return (START + (now - levelStarted) / stepMs()) % LEDS;
}

// True once for each new press, ignoring 30 ms of contact bounce.
bool pressed() {
  bool now = digitalRead(BUTTON);
  bool edge = now == LOW && lastButton == HIGH && millis() - buttonAt > 30;
  if (now != lastButton) buttonAt = millis();
  lastButton = now;
  return edge;
}

void drawGame(uint8_t light) {
  ring.clear();
  ring.setPixelColor(TARGET, ring.Color(0, 150, 0));
  ring.setPixelColor(light, ring.Color(255, 0, 0));
  ring.show();
}

void startLevel() {
  Serial.print("level ");
  Serial.print(level);
  Serial.print(": ");
  Serial.print(stepMs());
  Serial.println(" ms an LED");
  // The button was let go while the ring flashed; take its state as it is now,
  // so the next press counts at once.
  lastButton = digitalRead(BUTTON);
  levelStarted = millis();
}

void caught() {
  Serial.print("caught it on level ");
  Serial.println(level);
  // the whole ring flashes green, with a rising chirp
  for (uint8_t i = 0; i < 3; i++) {
    ring.fill(ring.Color(0, 200, 0));
    ring.show();
    tone(PIEZO, 1000 + i * 400, 80);
    delay(120);
    ring.clear();
    ring.show();
    delay(60);
  }
  level++;
  startLevel();
}

void missed(uint8_t light) {
  // how many LEDs off, the short way round
  uint8_t off = light > LEDS / 2 ? LEDS - light : light;
  Serial.print("stopped on LED ");
  Serial.print(light);
  Serial.print(", missed by ");
  Serial.print(off);
  Serial.print(off == 1 ? " LED" : " LEDs");
  Serial.print(": game over on level ");
  Serial.println(level);
  if (level > best) best = level;
  Serial.print("best level: ");
  Serial.println(best);
  tone(PIEZO, 140, 600);
  // show where it stopped, blinking
  for (uint8_t i = 0; i < 4; i++) {
    drawGame(light);
    delay(250);
    ring.setPixelColor(light, 0);
    ring.show();
    delay(250);
  }
  playing = false;
  Serial.println("press the button to start");
}

void setup() {
  Serial.begin(115200);
  pinMode(BUTTON, INPUT_PULLUP);
  pinMode(PIEZO, OUTPUT);
  ring.begin();
  ring.setBrightness(60);
  Serial.println("Stop the light: press the button to start");
}

void loop() {
  unsigned long now = millis();
  if (!playing) {
    // a slow rainbow while it waits
    for (uint8_t i = 0; i < LEDS; i++) {
      ring.setPixelColor(i, ring.ColorHSV((uint16_t)(i * 65536L / LEDS + now * 20)));
    }
    ring.show();
    if (pressed()) {
      playing = true;
      level = 1;
      startLevel();
    }
    return;
  }
  uint8_t light = lightAt(now);
  drawGame(light);
  if (pressed()) {
    if (light == TARGET) {
      caught();
    } else {
      missed(light);
    }
  }
}