#import<FastLED.h>
#define NUM_COLS 20
#define NUM_ROWS 20
#define NUM_LEDS 256
CRGB leds [256];
void setup()
{
LEDS.addLeds<WS2812, 3, GRB>(leds, 256);
}
byte idx = 0;
void loop() {
leds[idx] = CRGB::Red;
FastLED.show();
leds[idx] = 0;
idx++;
delay(10);
}