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

#include QMK_KEYBOARD_H

// Each layer gets a name for readability, which is then used in the keymap matrix below.
// The underscores don't mean anything - you can have a layer called STUFF or any other name.
// Layer names don't all need to be of the same length, obviously, and you can also skip them
// entirely and just use numbers.
#define _QW 0
#define _RS 1
#define _LW 2

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
  [_QW] = LAYOUT( /* Qwerty */
    KC_Q,    KC_W,    KC_E,    KC_R,    KC_T,                      KC_Y,    KC_U,    KC_I,    KC_O,    KC_P    ,
    KC_A,    KC_S,    KC_D,    KC_F,    KC_G,                      KC_H,    KC_J,    KC_K,    KC_L,    KC_SCLN ,
    KC_Z,    KC_X,    KC_C,    KC_V,    KC_B,                      KC_N,    KC_M,    KC_COMM, KC_DOT,  KC_SLSH ,
    KC_ESC,  KC_TAB, KC_LGUI,  KC_LSFT, KC_BSPC, KC_LCTL, KC_LALT, KC_SPC,  MO(_RS), KC_MINS, KC_QUOT, KC_ENT
  ),

  [_RS] = LAYOUT( /* [> RAISE <] */
    KC_EXLM, KC_AT,   KC_LCBR, KC_RCBR, KC_PIPE,                   KC_PGUP, KC_7,    KC_8,   KC_9, KC_ASTR ,
    KC_HASH, KC_DLR,  KC_LPRN, KC_RPRN, KC_GRV,                    KC_PGDN, KC_4,    KC_5,   KC_6, KC_PLUS ,
    KC_PERC, KC_CIRC, KC_LBRC, KC_RBRC, KC_TILD,                   KC_AMPR, KC_1,    KC_2,   KC_3, KC_BSLS ,
    TG(_LW), KC_INS,  KC_LGUI, KC_LSFT, KC_BSPC, KC_LCTL, KC_LALT, KC_SPC,  KC_TRNS, KC_DOT, KC_0, KC_EQL
  ),

  [_LW] = LAYOUT( /* [> LOWER <] */
    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_DOWN,                   KC_DOWN, KC_F4,   KC_F5,   KC_F6,   KC_F11 ,
    KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS,                   KC_TRNS, KC_F1,   KC_F2,   KC_F3,   KC_F12 ,
    KC_TRNS, KC_TRNS, KC_LGUI, KC_LSFT, KC_BSPC, KC_LCTL, KC_LALT, KC_SPC,  DF(_QW), KC_TRNS, KC_TRNS, QK_BOOT
  ),
};