Digital Rain

//Digital Rain implementation
//fastled 16x16 matrix demo
//Yaroslaw Turbin 24.08.2020
//https://vk.com/ldirko
//https://www.reddit.com/user/ldirko/

#include "FastLED.h"

// Matrix size
#define NUM_ROWS 16
#define NUM_COLS 16
// LEDs pin
#define DATA_PIN 3
// LED brightness
#define BRIGHTNESS 255
#define NUM_LEDS NUM_ROWS * NUM_COLS
// Define the array of leds
CRGB leds[NUM_LEDS];
byte rain[NUM_LEDS];
byte counter = 1;
int speed = 1;

void setup() {
FastLED.addLeds<NEOPIXEL, DATA_PIN>(leds, NUM_LEDS);
FastLED.setBrightness(BRIGHTNESS);
raininit();
}

void loop() {
EVERY_N_MILLISECONDS(100) {
updaterain();
FastLED.show();
}
EVERY_N_MILLISECONDS(30) {changepattern();}
} //loop

void changepattern () {
int rand1 = random16 (NUM_LEDS);
int rand2 = random16 (NUM_LEDS);
if ((rain[rand1] == 1) && (rain[rand2] ==0) )    //simple get two random dot 1 and 0 and swap it,
    {rain[rand1] = 0; rain[rand2] = 1;}           //this will not change total number of dots
} //changepattern

void raininit() {                               //init array of dots. run once
for (int i = 0; i < NUM_LEDS; i++) {
if (random8(20) == 0) { rain[i] = 1; }       //random8(20) number of dots. decrease for more dots
                 else { rain[i] = 0; }
}
} //raininit

void updaterain() {
for (byte i = 0; i < NUM_COLS; i++) {
for (byte j = 0; j < NUM_ROWS; j++) {
byte layer = rain[XY(i, ((j + speed + random8(2) + NUM_ROWS) % NUM_ROWS))];   //fake scroll based on shift coordinate
                                                                              // random8(2) add glitchy look
if (layer) { leds[XY((NUM_COLS - 1) - i, (NUM_ROWS - 1) - j)] = CHSV(110, 255, BRIGHTNESS); }
}}

speed ++;
fadeToBlackBy(leds, NUM_LEDS, 40);
blurRows(leds, NUM_COLS, NUM_ROWS, 16);      //if you want
}//updaterain

uint16_t XY (uint8_t x, uint8_t y) { return (y * NUM_COLS + x);}