FastLED ColorFromPalette For-Loop Replace with Millis()

//please declare variables

static uint8_t startIndex = 0;

void loop()
{
    //ChangePalettePeriodically();

    //static uint8_t startIndex = 0;
    //startIndex = startIndex + 1; /* motion speed */

    //FillLEDsFromPaletteColors( startIndex);
    FillLEDsFromPaletteColors2( startIndex);

    //FastLED.show();
    //FastLED.delay(1000 / UPDATES_PER_SECOND);
}



// Original

void FillLEDsFromPaletteColors( uint8_t colorIndex)
{
    uint8_t brightness = 255;

    for( int i = 0; i < NUM_LEDS; ++i) {
        leds[i] = ColorFromPalette( currentPalette, colorIndex, brightness, currentBlending);
        colorIndex += 3;
    }
}

// For-loop switched for millis()
void FillLEDsFromPaletteColors2(){

  currentPalette = RainbowStripeColors_p;

  static uint8_t temp_index = startIndex; //initialize once for colorfrompalette

  if(isLoaded == false){  //leds arent loaded. do nothing but load data
    if(x < NUM_LEDS){   //original for-loop condition for(int i =0; x<NUM_LEDS;i++)
      leds[x] = ColorFromPalette( currentPalette, temp_index, 40, currentBlending );
      temp_index += 3;
      x++;  //original for-loop incrementor
    }else if(x == NUM_LEDS){  //leds are full,
      x = 0;
      isLoaded = true;    //leds are finally loaded, reset x and wait for timer
    }
  }

  if(millis() - previousMillis >= (20) && isLoaded == true){  //our fastled delay(20)
    previousMillis = millis();
    isLoaded = false;          //leds will no longer be loaded at FastLED show is called
    startIndex += 1;
    temp_index = startIndex;    //reset temp_index to start index to move led to next
    FastLED.show();           //no longer loaded
  }
}