FastLED TwinkLEDS with various delays

// TwinkLEDS with various delays
//
// By: Andrew Tuline
//
// Date: Aug, 2014
//
// This is a simple FastLED (2.1 and greater) display sequence template with a non-blocking delay.
//
// I don't know why twinkle2() doesn't work.
//
//
// FastLED 2.1 is available at https://github.com/FastLED/FastLED/tree/FastLED2.1
//


#include <FastLED.h>                                           // FastLED library

#define LED_DT 13                                              // Data pin
#define NUM_LEDS 24                                            // Number of LED's
#define COLOR_ORDER GRB                                        // Change the order as necessary
#define LED_TYPE WS2811                                        // What kind of strip are you using?
#define BRIGHTNESS  196                                        // How bright do we want to go

struct CRGB leds[NUM_LEDS];                                    // Initializxe our array


// Initialize global variables for sequences
int thisdelay = 8;                                             // A delay value for the sequence(s)

// Non-blocking delay timers
long currentMillis = 0;
long previousMillis = 0;


void setup() {
  Serial.begin(9600);
  LEDS.addLeds<LED_TYPE, LED_DT, COLOR_ORDER>(leds, NUM_LEDS).setCorrection(TypicalLEDStrip);
  FastLED.setBrightness(BRIGHTNESS);
} // setup()


void loop () {
//  twinkle();                                                   // Use blocking delay - THIS WORKS!!
 twinkle2();                                                   // Use non-blocking delay - THIS DOES NOT WORK!!
//  twinkle3();                                                  // Uses non-blocking delay with print statements -- THIS WORKS!!
} // loop()


void twinkle() {
  int i = random8();                                                                     // A random number. Higher number => fewer twinkles. Use random16() for values >255.
  if (i < NUM_LEDS) leds[i] = CHSV(50, 100, 255);              // Only the lowest probability twinkles will do. You could even randomize the hue/saturation. .
  for (int j = 0; j < NUM_LEDS; j++) leds[j].fadeToBlackBy(8);
  LEDS.show();                                                 // Standard FastLED display
  delay(thisdelay);                                            // Standard delay
} // twinkle()


void twinkle2() {                                              // This does not work correctly for some reason.
currentMillis = millis();
  if(currentMillis - previousMillis > thisdelay) {
    int i = random8();                                         // A random number. Higher number => fewer twinkles. Use random16() for values >255.
    if (i < NUM_LEDS) leds[i] = CHSV(50, 100, 255);            // Only the lowest probability twinkles will do. You could even randomize the hue/saturation. .
    for (int j = 0; j < NUM_LEDS; j++) leds[j].fadeToBlackBy(8);
    LEDS.show();                                               // Standard FastLED display
  }
  previousMillis = currentMillis;
} // twinkle2()


void twinkle3() {
currentMillis = millis();

  Serial.print(currentMillis);                                 // For some reason, the non-blocking delay works when I add a few print statements.
  Serial.print(" ");
  Serial.println(previousMillis);

  if(currentMillis - previousMillis > thisdelay) {
    int i = random8();                                         // A random number. Higher number => fewer twinkles. Use random16() for values >255.
    if (i < NUM_LEDS) leds[i] = CHSV(50, 100, 255);            // Only the lowest probability twinkles will do. You could even randomize the hue/saturation. .
    for (int j = 0; j < NUM_LEDS; j++) leds[j].fadeToBlackBy(8);
    LEDS.show();                                               // Standard FastLED display
  }
  previousMillis = currentMillis;
} // twinkle3()