qmk-firmware/quantum/led_matrix/animations/solid_reactive_cross.h

#ifdef LED_MATRIX_KEYREACTIVE_ENABLED
#    if defined(ENABLE_LED_MATRIX_SOLID_REACTIVE_CROSS) || defined(ENABLE_LED_MATRIX_SOLID_REACTIVE_MULTICROSS)

#        ifdef ENABLE_LED_MATRIX_SOLID_REACTIVE_CROSS
LED_MATRIX_EFFECT(SOLID_REACTIVE_CROSS)
#        endif

#        ifdef ENABLE_LED_MATRIX_SOLID_REACTIVE_MULTICROSS
LED_MATRIX_EFFECT(SOLID_REACTIVE_MULTICROSS)
#        endif

#        ifdef LED_MATRIX_CUSTOM_EFFECT_IMPLS

static uint8_t SOLID_REACTIVE_CROSS_math(uint8_t val, int16_t dx, int16_t dy, uint8_t dist, uint16_t tick) {
    uint16_t effect = tick + dist;
    dx              = dx < 0 ? dx * -1 : dx;
    dy              = dy < 0 ? dy * -1 : dy;
    dx              = dx * 16 > 255 ? 255 : dx * 16;
    dy              = dy * 16 > 255 ? 255 : dy * 16;
    effect += dx > dy ? dy : dx;
    if (effect > 255) effect = 255;
    return qadd8(val, 255 - effect);
}

#            ifdef ENABLE_LED_MATRIX_SOLID_REACTIVE_CROSS
bool SOLID_REACTIVE_CROSS(effect_params_t* params) {
    return effect_runner_reactive_splash(qsub8(g_last_hit_tracker.count, 1), params, &SOLID_REACTIVE_CROSS_math);
}
#            endif

#            ifdef ENABLE_LED_MATRIX_SOLID_REACTIVE_MULTICROSS
bool SOLID_REACTIVE_MULTICROSS(effect_params_t* params) {
    return effect_runner_reactive_splash(0, params, &SOLID_REACTIVE_CROSS_math);
}
#            endif

#        endif // LED_MATRIX_CUSTOM_EFFECT_IMPLS
#    endif     // defined(ENABLE_LED_MATRIX_SOLID_REACTIVE_CROSS) || defined(ENABLE_LED_MATRIX_SOLID_REACTIVE_MULTICROSS)
#endif         // LED_MATRIX_KEYREACTIVE_ENABLED