LED blink patterns with multiple LEDs with millis() not using Delay()

Question

I want to make LED blink patterns with multiple LEDs with the millis() function. I researched about it but did not find a perfect solution.

I found one blog, but it is using a LED pin number array; I need a solution without an array. Any help will be appreciated.

This is my code which I have written:

const int Button_code_1 = 2;
const int Button_code_2 = 3;
const int Button_code_stop = 4;

const int LED_one = 6;
const int LED_two = 8;
const int LED_three = 10;
const int LED_four = 12;

int buttonState_code_1 = 0;
int buttonState_code_2 = 0;
int buttonState_code_stop = 0;

void setup() {
  // put your setup code here, to run once:

  Serial.begin(9600);

  pinMode(Button_code_1,INPUT);
  pinMode(Button_code_2,INPUT);
  pinMode(Button_code_stop,INPUT);

  pinMode(LED_Button_one,INPUT);
  pinMode(LED_Button_two,INPUT);
  pinMode(LED_Button_three,INPUT);
  pinMode(LED_Button_four,INPUT);
  
  pinMode(LED_one, OUTPUT);
  pinMode(LED_two, OUTPUT);
  pinMode(LED_three, OUTPUT);
  pinMode(LED_four, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:

  buttonState_code_1 = digitalRead(Button_code_1);
  Serial.println(buttonState_code_1);
  buttonState_code_2 = digitalRead(Button_code_2);
  Serial.println(buttonState_code_2);
  delay(1000);
  buttonState_code_stop = digitalRead(Button_code_stop);
  
  if(buttonState_code_1==1)
  {
    pattern_one();
  }
  if(buttonState_code_2==1)
  {
    pattern_two();
  }

}

void pattern_one()
{
  digitalWrite(LED_one, LOW);
  digitalWrite(LED_two, HIGH);
  digitalWrite(LED_three, LOW);
  digitalWrite(LED_four, LOW);
  delay(3000);
  digitalWrite(LED_one, LOW);
  digitalWrite(LED_two, LOW);
  digitalWrite(LED_three, LOW);
  digitalWrite(LED_four, HIGH);
  delay(3000);
  digitalWrite(LED_one, HIGH);
  digitalWrite(LED_two, LOW);
  digitalWrite(LED_three, LOW);
  digitalWrite(LED_four, LOW);
  delay(3000);
  digitalWrite(LED_one, LOW);
  digitalWrite(LED_two, LOW);
  digitalWrite(LED_three, HIGH);
  digitalWrite(LED_four, LOW);
  delay(3000);
}

void pattern_two()
{
  digitalWrite(LED_one, HIGH);
  digitalWrite(LED_two, LOW);
  digitalWrite(LED_three, LOW);
  digitalWrite(LED_four, LOW);
  delay(3000);
  digitalWrite(LED_one, LOW);
  digitalWrite(LED_two, LOW);
  digitalWrite(LED_three, HIGH);
  digitalWrite(LED_four, LOW);
  delay(3000);
  digitalWrite(LED_one, LOW);
  digitalWrite(LED_two, HIGH);
  digitalWrite(LED_three, LOW);
  digitalWrite(LED_four, LOW);
  delay(3000);
  digitalWrite(LED_one, LOW);
  digitalWrite(LED_two, LOW);
  digitalWrite(LED_three, LOW);
  digitalWrite(LED_four, HIGH);
  delay(3000);
}

This is my sample code with four LEDs. I have written this code with delay(), so when I want to change the pattern I can't because delay() is blocking the code.

I researched this and found the millis() function as the solution. How can I implement this code using the millis() function?

Answer 1

This is one of the effects for 3 (sets) of LEDs from my light alarm clock sketch:

void cycleEffect() {

  static unsigned long previousMillis;
  static uint8_t cycleCounter;

  if (millis() - previousMillis > 100) {
    previousMillis = millis();
    digitalWrite(LEDS_CENTRAL_PIN, cycleCounter == 0);
    digitalWrite(LEDS_LEFT_PIN, cycleCounter == 1);
    digitalWrite(LEDS_RIGHT_PIN, cycleCounter == 2);
    cycleCounter++;
    if (cycleCounter == 3) {
      cycleCounter = 0;
    }
  }
}