qmk-firmware/quantum/rgb_matrix_animations/solid_reactive_cross.h

#ifdef RGB_MATRIX_KEYREACTIVE_ENABLED
#if !defined(DISABLE_RGB_MATRIX_SOLID_REACTIVE_CROSS) || !defined(DISABLE_RGB_MATRIX_SOLID_REACTIVE_MULTICROSS)

#ifndef DISABLE_RGB_MATRIX_SOLID_REACTIVE_CROSS
RGB_MATRIX_EFFECT(SOLID_REACTIVE_CROSS)
#endif

#ifndef DISABLE_RGB_MATRIX_SOLID_REACTIVE_MULTICROSS
RGB_MATRIX_EFFECT(SOLID_REACTIVE_MULTICROSS)
#endif

#ifdef RGB_MATRIX_CUSTOM_EFFECT_IMPLS

static bool rgb_matrix_solid_reactive_multicross_range(uint8_t start, effect_params_t* params) {
  RGB_MATRIX_USE_LIMITS(led_min, led_max);

  HSV hsv = { rgb_matrix_config.hue, rgb_matrix_config.sat, 0 };
  uint8_t count = g_last_hit_tracker.count;
  for (uint8_t i = led_min; i < led_max; i++) {
    hsv.v = 0;
    for (uint8_t j = start; j < count; j++) {
      RGB_MATRIX_TEST_LED_FLAGS();
      int16_t dx = g_led_config.point[i].x - g_last_hit_tracker.x[j];
      int16_t dy = g_led_config.point[i].y - g_last_hit_tracker.y[j];
      uint8_t dist = sqrt16(dx * dx + dy * dy);
      int16_t dist2 = 16;
      uint8_t dist3;
      uint16_t effect = scale16by8(g_last_hit_tracker.tick[j], rgb_matrix_config.speed) + dist;
      dx = dx < 0 ? dx * -1 : dx;
      dy = dy < 0 ? dy * -1 : dy;
      dx = dx * dist2 > 255 ? 255 : dx * dist2;
      dy = dy * dist2 > 255 ? 255 : dy * dist2;
      dist3 = dx > dy ? dy : dx;
      effect += dist3;
      if (effect > 255)
        effect = 255;
      hsv.v = qadd8(hsv.v, 255 - effect);
    }
    hsv.v = scale8(hsv.v, rgb_matrix_config.val);
    RGB rgb = hsv_to_rgb(hsv);
    rgb_matrix_set_color(i, rgb.r, rgb.g, rgb.b);
  }
  return led_max < DRIVER_LED_TOTAL;
}

bool SOLID_REACTIVE_MULTICROSS(effect_params_t* params) {
  return rgb_matrix_solid_reactive_multicross_range(0, params);
}

bool SOLID_REACTIVE_CROSS(effect_params_t* params) {
  return rgb_matrix_solid_reactive_multicross_range(qsub8(g_last_hit_tracker.count, 1), params);
}

#endif // RGB_MATRIX_CUSTOM_EFFECT_IMPLS
#endif // !defined(DISABLE_RGB_MATRIX_SOLID_REACTIVE_CROSS) || !defined(DISABLE_RGB_MATRIX_SOLID_REACTIVE_MULTICROSS)
#endif // RGB_MATRIX_KEYREACTIVE_ENABLED