#include <Adafruit_NeoPixel.h>

#define MATRIX_PIN 2
#define ROWS 8
#define COLS 8
#define NUM_PIXELS (ROWS * COLS)

Adafruit_NeoPixel matrix(NUM_PIXELS, MATRIX_PIN, NEO_GRB + NEO_KHZ800);

uint32_t Wheel(byte WheelPos) {
  WheelPos = 255 - WheelPos;
  if (WheelPos < 85) {
    return matrix.Color(255 - WheelPos * 3, 0, WheelPos * 3);
  } else if (WheelPos < 170) {
    WheelPos -= 85;
    return matrix.Color(0, WheelPos * 3, 255 - WheelPos * 3);
  } else {
    WheelPos -= 170;
    return matrix.Color(WheelPos * 3, 255 - WheelPos * 3, 0);
  }
}

void setup() {
  matrix.begin();
  matrix.setBrightness(50);
  matrix.show();
}

void loop() {
  static uint16_t offset = 0;

  for (int row = 0; row < ROWS; row++) {
    for (int col = 0; col < COLS; col++) {
      int pixel = row * COLS + col;
      // Spread rainbow across rows and columns
      byte colorIndex = ((row + col) * 256 / (ROWS + COLS) + offset) & 255;
      matrix.setPixelColor(pixel, Wheel(colorIndex));
    }
  }
  matrix.show();

  offset = (offset + 1) & 255;
  delay(30);
}