#include <FastLED.h>

#define LED_PIN  5
#define COLOR_ORDER GRB
#define CHIPSET     WS2811

#define BRIGHTNESS 32

const uint8_t kMatrixWidth  = 16;
const uint8_t kMatrixHeight = 16;
const bool    kMatrixSerpentineLayout = true;

#define NUM_LEDS (kMatrixWidth * kMatrixHeight)
CRGB leds[NUM_LEDS];

void setup() {
  FastLED.addLeds<CHIPSET, LED_PIN, COLOR_ORDER>(leds, NUM_LEDS);
  FastLED.setBrightness( BRIGHTNESS );
}

void loop()
{
    uint32_t ms = millis();
    int32_t yHueDelta32 = ((int32_t)cos16( ms * 27 ) * (350 / kMatrixWidth));
    int32_t xHueDelta32 = ((int32_t)cos16( ms * 39 ) * (310 / kMatrixHeight));
    DrawOneFrame( ms / 65536, yHueDelta32 / 32768, xHueDelta32 / 32768);
    FastLED.show();
}

void DrawOneFrame( byte startHue8, int8_t yHueDelta8, int8_t xHueDelta8)
{
  byte lineStartHue = startHue8;
  for( byte y = 0; y < kMatrixHeight; y++) {
    lineStartHue += yHueDelta8;
    byte pixelHue = lineStartHue;
    for( byte x = 0; x < kMatrixWidth; x++) {
      pixelHue += xHueDelta8;
      leds[ XY(x, y)]  = CHSV( pixelHue, 255, 255);
    }
  }
}

// Helper function that translates from x, y into an index into the LED array
// Handles both 'row order' and 'serpentine' pixel layouts.
uint16_t XY( uint8_t x, uint8_t y)
{
  uint16_t i;

  if( kMatrixSerpentineLayout == false) {
    i = (y * kMatrixWidth) + x;
  } else {
    if( y & 0x01) {
      // Odd rows run backwards
      uint8_t reverseX = (kMatrixWidth - 1) - x;
      i = (y * kMatrixWidth) + reverseX;
    } else {
      // Even rows run forwards
      i = (y * kMatrixWidth) + x;
    }
  }

  return i;
}