qmk_firmware/quantum/rgb_matrix/animations/solid_reactive_simple_anim.h

#ifdef RGB_MATRIX_KEYREACTIVE_ENABLED
#    ifdef ENABLE_RGB_MATRIX_SOLID_REACTIVE_SIMPLE
RGB_MATRIX_EFFECT(SOLID_REACTIVE_SIMPLE)
#        ifdef RGB_MATRIX_CUSTOM_EFFECT_IMPLS

static HSV SOLID_REACTIVE_SIMPLE_math(HSV hsv, uint16_t offset) {
#            ifdef RGB_MATRIX_SOLID_REACTIVE_GRADIENT_MODE
    hsv.h = scale16by8(g_rgb_timer, add8(rgb_matrix_config.speed, 1) >> 6);
#            endif
    hsv.v = scale8(255 - offset, hsv.v);
    return hsv;
}

bool SOLID_REACTIVE_SIMPLE(effect_params_t* params) {
    return effect_runner_reactive(params, &SOLID_REACTIVE_SIMPLE_math);
}

#        endif // RGB_MATRIX_CUSTOM_EFFECT_IMPLS
#    endif     // ENABLE_RGB_MATRIX_SOLID_REACTIVE_SIMPLE
#endif         // RGB_MATRIX_KEYREACTIVE_ENABLED