#include <LiquidCrystal_I2C.h>

static const auto COLUMNS = 16;
static const auto ROWS_PER_SCREEN = 2;

static LiquidCrystal_I2C lcds[] = {
  {0x27, COLUMNS, ROWS_PER_SCREEN},
  {0x28, COLUMNS, ROWS_PER_SCREEN},
  {0x29, COLUMNS, ROWS_PER_SCREEN},
};

static const auto TOTAL_ROWS = (int)(std::size(lcds) * ROWS_PER_SCREEN);

void setup() {
  for (auto& lcd : lcds)
    lcd.init();
}

void loop() {
  static auto position = 0;
  static auto delta = 1;

  if (position >= TOTAL_ROWS * COLUMNS) {
    delta = -1;
    position = TOTAL_ROWS * COLUMNS - 1;
  }

  if (position < 0) {
    delta = 1;
    position = 0;
  }

  auto column = position % COLUMNS;
  auto row = position / COLUMNS;

  auto screen = row / ROWS_PER_SCREEN;
  auto screen_row = row % ROWS_PER_SCREEN;

  auto lcd = lcds[screen];

  lcd.setCursor(column, screen_row);
  if (delta > 0)
    lcd.print("\xff");
  else
    lcd.print(" ");

  position += delta;

  delay(10);
}