qmk-firmware/keyboards/handwired/gamenum/gamenum.h

#pragma once

#include "quantum.h"

#define XXX KC_NO

#define LAYOUT( \
    k00, k01, k02, k03, \
    k10, k11, k12, k13, \
    k20, k21, k22, \
    k30, k31, k32, \
         k41, k42, k43 \
) { \
    { k00, k01, k02, k03 }, \
    { k10, k11, k12, k13 }, \
    { k20, k21, k22, XXX }, \
    { k30, k31, k32, XXX }, \
    { XXX, k41, k42, k43 } \
}