qmk_firmware/quantum/rgb_matrix_animations/cycle_out_in_anim.h

#ifndef DISABLE_RGB_MATRIX_CYCLE_OUT_IN
RGB_MATRIX_EFFECT(CYCLE_OUT_IN)
#    ifdef RGB_MATRIX_CUSTOM_EFFECT_IMPLS

static HSV CYCLE_OUT_IN_math(HSV hsv, int16_t dx, int16_t dy, uint8_t dist, uint8_t time) {
    hsv.h = 3 * dist / 2 + time;
    return hsv;
}

bool CYCLE_OUT_IN(effect_params_t* params) { return effect_runner_dx_dy_dist(params, &CYCLE_OUT_IN_math); }

#    endif  // RGB_MATRIX_CUSTOM_EFFECT_IMPLS
#endif      // DISABLE_RGB_MATRIX_CYCLE_OUT_IN