#include "FastLED.h"
// Matrix size
#define HEIGHT 16
#define WIDTH 16
#define NUM_LEDS WIDTH * HEIGHT
#define MATRIX_TYPE 1
#define DATA_PIN 3                // LEDs pin
#define BRIGHTNESS 255            // LED brightness
CRGB leds[NUM_LEDS];              // Define the array of leds
// ******************************************************************************
int offset = 0;
int offset2 = 0;
int offset3 = offset + offset2;
// ******************************************************************************


uint16_t XY (uint8_t x, uint8_t y) {
  return (y * WIDTH + x);
}

void setup() {
  FastLED.addLeds<NEOPIXEL, DATA_PIN>(leds, NUM_LEDS);
  FastLED.setBrightness(BRIGHTNESS);
  pinMode(2, INPUT_PULLUP);
}

void loop() {
 // ******************************************************************************
  EVERY_N_MILLISECONDS(20) {
    offset++;
    offset2++;
    offset3++;
  } 
  EVERY_N_MILLISECONDS(20) { 
    offset3++;
  }
  int length = max(max(HEIGHT, WIDTH) / 20, 10);
  int length2 = min(min(HEIGHT, WIDTH) / 50, 5);
  for (uint16_t x = 0; x < HEIGHT; x++) {
    for (uint16_t y = 0; y < WIDTH; y++) {
      uint16_t i = XY(x, y);
      if (x == 0 || x == HEIGHT - 1 || y == 0 || y == WIDTH - 1) {
        leds[i] = CHSV(x * length + y * length + offset, 255, 255);
      } 
      else if (x == 1 || x == HEIGHT - 2 || y == 1 || y == WIDTH - 2) {
        leds[i] = CHSV(x * length + y * length + offset, 255, 255);
      } 
      else if (x == HEIGHT / 2 - 1 || x == HEIGHT - HEIGHT / 2 || 
               y == WIDTH / 2 - 1 || y == WIDTH - WIDTH / 2) {
        leds[i] = CHSV(x * length + y * length + offset, 255, 255);
      } 
      else {
        leds[i] = CRGB::Black;
      }
    }
  }
 // ******************************************************************************
  FastLED.show();
  
} //loop