// This version uses bit-banged SPI.
// If you see tearing (jagged edges on the circles) try the version
// which uses AVR's hardware SPI peripheral:
// https://wokwi.com/arduino/projects/318868939929027156

#include <SPI.h>

#define MOSI 51

#define WS2812_NUM_LEDS 8

#define WS2812_RESET_PULSE 60
#define WS2812_BUFFER_SIZE (WS2812_NUM_LEDS * 24 + WS2812_RESET_PULSE)

uint8_t ws2812_buffer[WS2812_BUFFER_SIZE];

void ws2812_init(void) {
    memset(ws2812_buffer, 0, WS2812_BUFFER_SIZE);
    ws2812_send_spi();
}

void ws2812_send_spi(void) {
    SPI.transfer(ws2812_buffer, WS2812_BUFFER_SIZE);
}

#define WS2812_FILL_BUFFER(COLOR) \
    for( uint8_t mask = 0x80; mask; mask >>= 1 ) { \
        if( COLOR & mask ) { \
            *ptr++ = 0xfc; \
        } else { \
            *ptr++ = 0x80; \
        } \
    }

void ws2812_pixel(uint16_t led_no, uint8_t r, uint8_t g, uint8_t b) {
    uint8_t * ptr = &ws2812_buffer[24 * led_no];
    WS2812_FILL_BUFFER(g);
    WS2812_FILL_BUFFER(r);
    WS2812_FILL_BUFFER(b);
}

void ws2812_pixel_all(uint8_t r, uint8_t g, uint8_t b) {
    uint8_t * ptr = ws2812_buffer;
    for( uint16_t i = 0; i < WS2812_NUM_LEDS; ++i) {
        WS2812_FILL_BUFFER(g);
        WS2812_FILL_BUFFER(r);
        WS2812_FILL_BUFFER(b);
    }
}

void setup() {
  Serial.begin(115200);
  pinMode(LED_BUILTIN, OUTPUT);

  SPI.beginTransaction(SPISettings(4000000, MSBFIRST, SPI_MODE0));
  
  ws2812_init();
}

void loop() {
  ws2812_pixel(0, 128, 0, 0);
  ws2812_send_spi();
    
  digitalWrite(LED_BUILTIN, HIGH);
  digitalWrite(MOSI, LOW);
  delay(100); 
}