qmk-firmware/quantum/rgb_matrix/animations/pixel_flow_anim.h

// Copyright 2022 @filterpaper
// SPDX-License-Identifier: GPL-2.0+

#ifdef ENABLE_RGB_MATRIX_PIXEL_FLOW
RGB_MATRIX_EFFECT(PIXEL_FLOW)
#    ifdef RGB_MATRIX_CUSTOM_EFFECT_IMPLS

static bool PIXEL_FLOW(effect_params_t* params) {
    // LED state array
    static RGB led[RGB_MATRIX_LED_COUNT];

    static uint32_t wait_timer = 0;
    if (wait_timer > g_rgb_timer) {
        return false;
    }

    inline uint32_t interval(void) {
        return 3000 / scale16by8(qadd8(rgb_matrix_config.speed, 16), 16);
    }

    if (params->init) {
        // Clear LEDs and fill the state array
        rgb_matrix_set_color_all(0, 0, 0);
        for (uint8_t j = 0; j < RGB_MATRIX_LED_COUNT; ++j) {
            led[j] = (random8() & 2) ? (RGB){0, 0, 0} : hsv_to_rgb((HSV){random8(), qadd8(random8() >> 1, 127), rgb_matrix_config.hsv.v});
        }
    }

    RGB_MATRIX_USE_LIMITS(led_min, led_max);
    // Light LEDs based on state array
    for (uint8_t i = led_min; i < led_max; ++i) {
        RGB_MATRIX_TEST_LED_FLAGS();
        rgb_matrix_set_color(i, led[i].r, led[i].g, led[i].b);
    }

    if (!rgb_matrix_check_finished_leds(led_max)) {
        // Shift LED state forward
        for (uint8_t j = 0; j < led_max - 1; ++j) {
            led[j] = led[j + 1];
        }
        // Fill last LED
        led[led_max - 1] = (random8() & 2) ? (RGB){0, 0, 0} : hsv_to_rgb((HSV){random8(), qadd8(random8() >> 1, 127), rgb_matrix_config.hsv.v});
        // Set pulse timer
        wait_timer = g_rgb_timer + interval();
    }

    return rgb_matrix_check_finished_leds(led_max);
}

#    endif // RGB_MATRIX_CUSTOM_EFFECT_IMPLS
#endif     // ENABLE_RGB_MATRIX_PIXEL_FLOW