Matrix LED Effect using FastLED

matrixEffect.ino

// Matrix effect by Jeremy Williams
// Designed for Game Frame
// http://www.ledseq.com

#include <FastLED.h>

// LED setup
#define kMatrixWidth  16
#define kMatrixHeight 16
#define DATA_PIN 2
#define CLOCK_PIN 4
#define NUM_LEDS 256
#define LED_TYPE APA102
#define COLOR_ORDER BGR
uint8_t ledBrightness = 64;

CRGB leds[NUM_LEDS];

void setup()
{
  // LED Init
  FastLED.addLeds<LED_TYPE, DATA_PIN, CLOCK_PIN, COLOR_ORDER>(leds, NUM_LEDS).setDither(0);
  FastLED.setBrightness(ledBrightness);
  FastLED.show();
}

void loop()
{
  EVERY_N_MILLIS(75) // falling speed
  {
    // move code downward
    // start with lowest row to allow proper overlapping on each column
    for (int8_t row=kMatrixHeight-1; row>=0; row--)
    {
      for (int8_t col=0; col<kMatrixWidth; col++)
      {
        if (leds[getIndex(col, row)] == CRGB(175,255,175))
        {
          leds[getIndex(col, row)] = CRGB(27,130,39); // create trail
          if (row < kMatrixHeight-1) leds[getIndex(col, row+1)] = CRGB(175,255,175);
        }
      }
    }

    // fade all leds
    for(int i = 0; i < NUM_LEDS; i++) {
      if (leds[i].g != 255) leds[i].nscale8(192); // only fade trail
    }

    // check for empty screen to ensure code spawn
    bool emptyScreen = true;
    for(int i = 0; i < NUM_LEDS; i++) {
      if (leds[i])
      {
        emptyScreen = false;
        break;
      }
    }

    // spawn new falling code
    if (random8(3) == 0 || emptyScreen) // lower number == more frequent spawns
    {
      int8_t spawnX = random8(kMatrixWidth);
      leds[getIndex(spawnX, 0)] = CRGB(175,255,175 );
    }

    FastLED.show();
  }
}

// convert x/y cordinates to LED index on zig-zag grid
uint16_t getIndex(uint16_t x, uint16_t y)
{
  uint16_t index;
  if (y == 0)
  {
    index = x;
  }
  else if (y % 2 == 0)
  {
    index = y * kMatrixWidth + x;
  }
  else
  {
    index = ((y * kMatrixWidth) + (kMatrixWidth-1)) - x;
  }
  return index;
}