#include <FastLED.h>

// Each group has 4 LEDs horizontally, then 12 LEDs vertically
#define X_SPAN 4
#define Y_SPAN 12

// There are 3 of these groups in total
#define XY_SPANS 3

#define NUM_LEDS ( (XY_SPANS) * ( (X_SPAN) + (Y_SPAN) ) )
CRGB leds[NUM_LEDS];


void setup() {
  FastLED.addLeds<WS2812B, 2, GRB>(leds, NUM_LEDS);
  FastLED.setCorrection(UncorrectedColor);
  FastLED.setTemperature(UncorrectedTemperature);
}


void loop() {
  static uint16_t ledno = 0;
  leds[ledno] = CRGB::White;
  FastLED.show();
  FastLED.clear();
  ledno = (ledno + 1) % NUM_LEDS;
  delay(100);
}