请问这段流水灯代码怎样让他变成逆向的（arduino）

#include <Adafruit_NeoPixel.h>
#ifdef __AVR__
  #include <avr/power.h>
#endif
#define PIN            6
#define NUMPIXELS      60
 
Adafruit_NeoPixel pixels = Adafruit_NeoPixel(NUMPIXELS, PIN, NEO_GRB + NEO_KHZ800);
 
int delayval = 20; // delay for half a second
int snakeLen = 10;  // snake's len
int endDex; // snake end's index
int dex = 0; // the start index
bool isNext = true;
void setup() {
#if defined (__AVR_ATtiny85__)
  if (F_CPU == 16000000) clock_prescale_set(clock_div_1);
#endif
  pixels.begin();
  endDex = snakeLen; // only once
}
 
void loop() {
  if(isNext){ 
      isNext = false;
      colorWrap();
    }
}
void colorWrap(){
   for(int i=dex;i<snakeLen;i++){
    pixels.setPixelColor(i%NUMPIXELS, pixels.Color(50,50,50)); // i%167 because run second circle for reset
    pixels.show(); 
    delay(delayval); 
    if(i == dex + (endDex-1)){
         isNext = true;
         pixels.setPixelColor(dex%NUMPIXELS, pixels.Color(1,1,1)); // close the led in the end
         pixels.show();
         dex ++;
         snakeLen ++;
      }
  }
 }