// https://www.reddit.com/r/FastLED/comments/1am4bn5/trouble_wrapping_around_a_ring_with_crgbset/

#include <FastLED.h>

#define DATA_PIN    PB1
#define NUM_LEDS    96
#define BRIGHTNESS  255
CRGB leds[NUM_LEDS];

const long outerInterval = 20;
int dot = 0;
int increment = 12;

void setup() {
  FastLED.addLeds<WS2811, DATA_PIN, RGB>(leds, NUM_LEDS);
  FastLED.setCorrection(TypicalPixelString);
  FastLED.setBrightness(BRIGHTNESS);
}

void loop() {
  EVERY_N_MILLIS(outerInterval) {
    for (uint8_t ledpos = 0; ledpos < NUM_LEDS; ledpos++) {
      CRGB col = CRGB::Black;
      if ((ledpos + dot) % (increment * 2) < increment) {
        leds[ledpos] = CRGB::Blue;
      } else {
        leds[ledpos] = CRGB::Black;
      }
    }
    FastLED.show();

    if (--dot < 0) dot = NUM_LEDS - 1;
  }
}