#include <FastLED.h>

#define LED_PIN     3
#define LED_W       8
#define LED_H       8
#define NUM_LEDS    (LED_W * LED_H)

CRGB leds[NUM_LEDS];

uint8_t frame[LED_H][LED_W];   // indexed buffer
int8_t scrollX = 0;
uint8_t hueOffset = 0;

// ================= PALETTE =================

DEFINE_GRADIENT_PALETTE(wave_gp) {
  0,   0,   0,   64,
  64,  0,   128, 255,
  128, 0,   255, 128,
  192, 255, 255, 0,
  255, 255, 0,   0
};

CRGBPalette16 palette = wave_gp;

// ================= MATRIX MAP =================

uint16_t XY(uint8_t x, uint8_t y) {
  if (y & 1) {
    return (y * LED_W) + (LED_W - 1 - x); // serpentine
  } else {
    return (y * LED_W) + x;
  }
}

// ================= PATTERN =================

void buildPattern() {
  for (uint8_t y = 0; y < LED_H; y++) {
    for (uint8_t x = 0; x < LED_W; x++) {
      frame[y][x] = (x * 32) + (y * 16);
    }
  }
}

// ================= RENDER =================

void render() {
  for (uint8_t y = 0; y < LED_H; y++) {
    for (uint8_t x = 0; x < LED_W; x++) {

      uint8_t sx = (x + scrollX) % LED_W;
      uint8_t idx = frame[y][sx] + hueOffset;

      leds[XY(x, y)] = ColorFromPalette(
        palette,
        idx,
        200,
        LINEARBLEND
      );
    }
  }
  FastLED.show();
}

// ================= SETUP =================

void setup() {
  FastLED.addLeds<WS2812B, LED_PIN, GRB>(leds, NUM_LEDS);
  FastLED.setBrightness(120);

  buildPattern();
}

// ================= LOOP =================

void loop() {
  scrollX = (scrollX + 1) % LED_W;
  hueOffset++;

  render();
  delay(40);
}