qmk_firmware/keyboards/mixi/mixi.h

#pragma once

#include "quantum.h"

#define LAYOUT( \
        K00, K01, K02, \
        K10, K11, K12, \
        K20, K21, K22  \
        ) { \
    { K00,   K01,   K02 }, \
    { K10,   K11,   K12 }, \
    { K20,   K21,   K22 }  \
}