qmk_firmware/keyboards/atreus/keymaps/default/keymap.c

// this is the style you want to emulate.
// This is the canonical layout file for the Quantum project. If you want to add another keyboard,

#include QMK_KEYBOARD_H

#define RALT_A RALT_T(KC_A)
#define ALT_S LALT_T(KC_S)
#define CTL_D LCTL_T(KC_D)
#define GUI_F LGUI_T(KC_F)

#define GUI_J LGUI_T(KC_J)
#define CTL_K LCTL_T(KC_K)
#define ALT_L LALT_T(KC_L)
#define RALT_SCLN RALT_T(KC_SCLN)

#define I_SPC LT(1, KC_SPC)
#define I_BSPC LT(2, KC_BSPC)

// https://github.com/callum-oakley/qmk_firmware/tree/master/users/callum

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
  [0] = LAYOUT(
    KC_Q,   KC_W,   KC_E,   KC_R,   KC_T,                     KC_Y,   KC_U,   KC_I,   KC_O,   KC_P,
    RALT_A, ALT_S,  CTL_D,  GUI_F,  KC_G,                     KC_H,   GUI_J,  CTL_K,  ALT_L,  RALT_SCLN,
    KC_Z,   KC_X,   KC_C,   KC_V,   KC_B,    KC_GRV, KC_BSLS, KC_N,   KC_M,   KC_COMM,KC_DOT, KC_SLSH,
    KC_ESC, KC_TAB, XXXXXXX,KC_LSFT,I_BSPC,  XXXXXXX,XXXXXXX, KC_SPC, MO(1),  XXXXXXX,XXXXXXX,XXXXXXX
  ),

  [1] = LAYOUT(
    KC_ESC, KC_EXLM,KC_AT,  KC_DLR, KC_PERC,                  KC_PLUS,KC_7,   KC_8,   KC_9,   XXXXXXX,
    KC_LPRN,KC_MINS,KC_QUOT,KC_EQL, KC_RPRN,                  KC_0,   KC_1,   KC_2,   KC_3,   KC_BSPC,
    KC_LBRC,KC_RBRC,KC_HASH,KC_LCBR,KC_RCBR, KC_CIRC,KC_AMPR, KC_ASTR,KC_4,   KC_5,   KC_6,   KC_ENT,
    XXXXXXX,XXXXXXX,_______,_______,_______, XXXXXXX,XXXXXXX, _______,_______,KC_DOT, XXXXXXX,XXXXXXX
  ),

  [2] = LAYOUT(
    KC_TAB, KC_HOME,KC_UP,  KC_END, KC_PGUP,                  KC_UP,  KC_F7,  KC_F8,  KC_F9,  KC_F10,
    KC_DEL, KC_LEFT,KC_DOWN,KC_RGHT,KC_PGDN,                  KC_LEFT,KC_DOWN,KC_UP,  KC_RGHT,KC_BSPC,
    KC_NO,  KC_VOLU,KC_NO,  KC_NO,  RESET,   _______,_______, KC_NO,  KC_PGDN,KC_PGUP,KC_F3,  KC_ENT,
    TO(0),  KC_VOLD,_______,_______,_______, XXXXXXX,XXXXXXX, _______,_______,KC_PSCR,KC_SLCK,KC_PAUS
  ),

  [3] = LAYOUT(
    KC_INS, KC_HOME,KC_UP,  KC_END, KC_PGUP,                  KC_UP,  KC_F7,  KC_F8,  KC_F9, KC_F10,
    KC_DEL, KC_LEFT,KC_DOWN,KC_RGHT,KC_PGDN,                  KC_DOWN,KC_F4,  KC_F5,  KC_F6, KC_F11,
    KC_NO,  KC_VOLU,KC_NO,  KC_NO,  RESET,   _______,_______, KC_NO,  KC_F1,  KC_F2,  KC_F3, KC_F12,
    TO(0),  KC_VOLD,_______,_______,_______, XXXXXXX,XXXXXXX, _______,_______,KC_PSCR,KC_SLCK,KC_PAUS
  )
};

layer_state_t layer_state_set_user(layer_state_t state) {
    return update_tri_layer_state(state, 1, 2, 3);
}