Example code to produce the dual 'Knight Rider' effect in the 'Wearable Neopixel bike lights' project as described in this blog post: http://ecafe.org/blog/2014/01/18/wearable-neopixel-bike-lights.html

Wearable NeoPixel bike lights

#include <Adafruit_NeoPixel.h>

#define PIN 1
#define NUM_PIXELS 20
#define NUM_NODES 2

Adafruit_NeoPixel strip = Adafruit_NeoPixel(NUM_PIXELS, PIN, NEO_GRB +
NEO_KHZ800);

uint32_t state[NUM_PIXELS];

// Pixel positions start at 1
// start pixel, end pixel, direction of travel 1|2, initial pixel
position, color
uint32_t nodes[NUM_NODES][6] = {
  { 1, 10, 1, 5, 0xFF1000 },
  { 11, 20, 2, 20, 0xFFFFFF }
};

void setup() {
  strip.begin();
  strip.setBrightness(32);
  strip.show();
}

void loop() {
  fadeStrip(2);
  updateNodes();
  strip.show();
  delay(70);
}

void updateNodes() {
  for(int i = 0; i<NUM_NODES; i++) {
    switch(nodes[i][2]) {
      case 1:
        nodes[i][3]++;
        if(nodes[i][3] == nodes[i][1]) {
          nodes[i][2] = 2;
        }
        break;
      case 2:
        nodes[i][3]--;
        if(nodes[i][3] == nodes[i][0]) {
          nodes[i][2] = 1;
        }
        break;
    }
    strip.setPixelColor(nodes[i][3]-1, nodes[i][4]);
    state[nodes[i][3]-1] = nodes[i][4];
  }
}

void fadeStrip(uint8_t rate) {
  for(int i = 0; i<NUM_PIXELS; i++) {
    state[i] = dimColor(state[i], rate);
    strip.setPixelColor(i, state[i]);
  }
}

// Borrowed the below from NeoPixel-KnightRider
uint32_t dimColor(uint32_t color, uint8_t width) {
   return (((color&0xFF0000)/width)&0xFF0000) + (((color&0x00FF00)/width)&0x00FF00) + (((color&0x0000FF)/width)&0x0000FF);
}