#include <FastLED.h>

typedef struct {
  uint8_t r;
  uint8_t g;
  uint8_t b;
} rgb_t;

#define NUM_PIXELS 300
#define LED_PINOUT 17

rgb_t fastled_buffer[NUM_PIXELS];

void setup() {
  // put your setup code here, to run once:
  pinMode(LED_PINOUT, OUTPUT);
  FastLED.addLeds<WS2812B, LED_PINOUT, RGB>((CRGB*)fastled_buffer, NUM_PIXELS);

  for (int i = 0; i < NUM_PIXELS; ++i) {
    fastled_buffer[i].r = 0;
    fastled_buffer[i].g = 0;
    fastled_buffer[i].b = 0;
  }
}

int i = 0;

void loop() {
  delay(20);
  i += 1;
  if (i >= NUM_PIXELS) i -= NUM_PIXELS;

  for (int j = 0; j < NUM_PIXELS; ++j) {
    fastled_buffer[j].r = 0;
    fastled_buffer[j].g = 0;
    fastled_buffer[j].b = 0;
  }
  if (i%3 == 0)  fastled_buffer[i].r = 100;
  else if (i%3 == 1) fastled_buffer[i].g = 100;
  else fastled_buffer[i].b = 100;
  FastLED.show();
  printf("i = %d\n", i);
}