Twinkling tree LEDs?

main.cpp

#include <FastLED.h>

#define NUM_LEDS 150
#define LED_PIN 25
#define BRIGHTNESS 50

#define RED 0
#define GREEN 1
#define WHITE 2
#define OFF 3

#define MIN_FADE 100
#define MIN_START 200
#define UPDATE_FREQ 50
#define OFF_MOD 10

CRGB leds[NUM_LEDS];

uint8_t ledPalette[NUM_LEDS];
uint8_t ledColorIndex[NUM_LEDS];
uint8_t ledNextFade[NUM_LEDS];

// these palettes waste memory, but:
// 1) there's nothing else running in this memory, and
// 2) the added flexibility is worth it because of (1)

DEFINE_GRADIENT_PALETTE(red_gp) {
  0, 0, 0, 0,  // black
  160, 255, 0, 0,  // red
  255, 0, 0, 0  // black
};
DEFINE_GRADIENT_PALETTE(green_gp) {
  0, 0, 0, 0,  // black
  160, 0, 255, 0,  // green
  255, 0, 0, 0  // black
};
DEFINE_GRADIENT_PALETTE(white_gp) {
  0, 0, 0, 0,  // black
  160, 255, 255, 255,  // white
  255, 0, 0, 0  // black
};
CRGBPalette16 palettes[3] = {red_gp, green_gp, white_gp};

bool is_off(CRGB led) {
  return led.r == 0 && led.g == 0 && led.b == 0;
}

void seed_leds() {
  for (uint8_t i = 0; i < NUM_LEDS; i++) {
    // ignore leds that already have a colour
    if (!is_off(leds[i])) {
      continue;
    }
    // chance of being red, green, white, or weighted to stay off
    int pal = random8() % OFF_MOD;
    if (pal >= OFF) {
        continue;
    } else {
        ledPalette[i] = pal;
        ledColorIndex[i] = min((uint8_t) MIN_START, random8());
        ledNextFade[i] = min((uint8_t) MIN_FADE, random8());

        leds[i] = ColorFromPalette(palettes[ledPalette[i]], ledColorIndex[i]);
    }
  }
}

void fade_leds() {
  for (uint8_t i = 0; i < NUM_LEDS; i++) {
    if (is_off(leds[i])) {
      continue;
    }
    if (ledNextFade[i] > 0) {
      // don't fade yet
      ledNextFade[i]--;
    } else {
      // fade
      leds[i] = ColorFromPalette(palettes[ledPalette[i]], ledColorIndex[i]--);
    }
  }
}

void setup() {
  FastLED.addLeds<WS2812B, LED_PIN, GRB>(leds, NUM_LEDS);
  FastLED.setBrightness(BRIGHTNESS);

  FastLED.clear(true);
  seed_leds();
}


void loop() {
  EVERY_N_MILLISECONDS(UPDATE_FREQ) {
    fade_leds();
    seed_leds();
    FastLED.show();
  }

}