A board can fit inside one room: numbers describe the terrain, a list holds images, and actions change coordinates. JDR-Bot remains a scenario engine; movement and collision rules are written by the author.

On a 7-column board, a cell number is y * 7 + x. Coordinates start at 0, increasing rightwards and downwards. Cell (1, 1) is therefore number 8.

title: The garden
vars:
  x: 1
  y: 1
  cell: 0
lists:
  terrain: [
    0, 0, 0, 0, 0, 0, 0,
    0, 1, 1, 1, 1, 1, 0,
    0, 1, 1, 0, 1, 1, 0,
    0, 1, 1, 0, 1, 1, 0,
    0, 1, 1, 0, 1, 1, 0,
    0, 1, 1, 1, 1, 1, 0,
    0, 0, 0, 0, 0, 0, 0
  ]
  grid: []
  tiles: [
    /images/public/mini-doom/tileset.svg:4x4:0:0,
    /images/public/mini-doom/tileset.svg:4x4:1:0,
    /images/public/mini-doom/tileset.svg:4x4:3:0
  ]

The terrain holds 49 values in one list: 0 means wall and 1 means floor. Images come from the Mini Doom tileset supplied with the Web/Desktop project. On another host, provide that image too or change its address.

Add this automatic event and its room after the declarations:

global_events:
  - id: draw_board
    state: 'ON'
    do:
      - do:
          - list: grid
            keep: 0
          - for_each: floor
            in: terrain
            do:
              - {list: grid, append: 't_tiles[v_floor_v]_t'}
          - cell = v_y_v
          - cell * 7
          - cell + v_x_v
          - text_var: grid[v_cell_v]
            value: t_tiles[2]_t
rooms:
  - id: garden
    auto_refresh: true
    text: '[[grid:7:grid]]'

Combine the two blocks in one YAML file to view the board with Test. The text uses [[grid:7:grid]]; the same marker works in a HUD. Draw the terrain first and the player afterwards. This first example only displays the board; the rules come next.

1. Movement: calculate a destination, check coordinates, then read the terrain. Move only if the cell is free.
2. Key: a collection key: {x: 1, y: 5, taken: 0} stores its position and state. Compare coordinates after moving.
3. Exit: check position and key.taken before declaring victory.
4. Random placement: collect reachable floor cells in a list, then choose: random for one key. Use draw: random for several objects without reusing the same cell.

Choose positions during setup, not after every move. The scenario must ensure the selected cells are reachable: the grid does not find paths.

Create numbers, lists and collections under Globals > Variables. Add loops and operations in an event's do:, buttons in room actions, then the grid marker in a HUD. The Expert profile exposes all these fields.

Test walls, the key, the exit and Restart. Test data lets you inspect coordinates and lists in a separate window without resizing the game.

The source files include two French tutorials building La clé du jardin in five steps: TUTORIEL-2D-YAML.md and TUTORIEL-2D-EDITEUR.md. Matching YAML and .jdrproj files are in dev/exemples/tutoriel-2d/. Snake and Mini Doom provide larger examples.

See Lists and loops, Tiles and grids and Shortcuts.