#include "FastLED.h"

// Matrix size
#define NUM_ROWS 10
#define NUM_COLS 10

// LEDs pin
#define DATA_PIN 3

// LED brightness
#define BRIGHTNESS 180

#define NUM_LEDS NUM_ROWS * NUM_COLS

// Define the array of leds
CRGB leds[NUM_LEDS];

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

void loop() {
  DrawRow();
  FastLED.clear();
}

void DrawRow() {
  int offest = 5; //1...9 < NUM_COLS
  int speed = 200;
  int y ;
  int x ;
  for (y = 0; y < NUM_ROWS; y++) {
    if (y == 0) {
      for (x = 0; x < NUM_COLS; x++ ) {
        leds[NUM_ROWS * (NUM_COLS - y) - NUM_ROWS + x] = CRGB::White;
        if (x > offest - 1)
        {
          leds[NUM_ROWS * (NUM_COLS - y) - NUM_ROWS + x] = CRGB::White;
          leds[NUM_ROWS * (NUM_COLS - 1 - y) - NUM_ROWS + x - offest] = CRGB::White;
        }
        FastLED.delay(speed);
        FastLED.show();
      }
    }
    else if (y == NUM_ROWS - 1) {
      for (x = 5; x < NUM_COLS; x++ ) {
        leds[NUM_ROWS * (NUM_COLS - y) - NUM_ROWS + x] = CRGB::White;
        FastLED.delay(speed);
        FastLED.show();
      }
    }
    else {
      for (x = 5; x <= NUM_COLS - 1; x++ ) {
        leds[NUM_ROWS * (NUM_COLS - y) - NUM_ROWS + x] = CRGB::White;
        leds[NUM_ROWS * (NUM_COLS - 1 - y) - NUM_ROWS + x - offest] = CRGB::White;
        FastLED.delay(speed);
        FastLED.show();
      }
    }
  }
}