CLOSES #1471

docs/tiled-map-editing.md

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+# Tiled map editing (mod authoring)
+
+`tools/tiled_export.py` turns the imported ROM cache into a
+[Tiled](https://www.mapeditor.org) workspace, so maps can be edited in a
+real map editor and exported back out as a mod. The original had no map
+editor at all; the port's own map data is plain Lua, which is what makes
+this a data path rather than an asset path.
+
+Editing is done in our own Tiled build,
+[bryanthaboi/tiled_gen1recomp](https://github.com/bryanthaboi/tiled_gen1recomp/releases),
+which ships the `gen1-mod-export` extension the workspace relies on. Grab it
+from that repo's releases; upstream Tiled opens the workspace but cannot
+export a mod out of it.
+
+```sh
+python3 tools/tiled_export.py          # -> build/tiled/ (gitignored)
+```
+
+Then open `build/tiled/gen1.tiled-project` in that build of Tiled.
+
+- **The overworld is one surface.** All 222 maps become `maps/*.tmj`, and
+  `kanto.world` places the 36 connected overworld maps at their real
+  connection offsets. That world is pre-loaded (seeded into the workspace's
+  Tiled session), so opening any one overworld map draws its neighbors around
+  it and you scroll and edit straight across the seams. Everything else is a
+  double-click away in Tiled's project panel.
+- **Extending Kanto wires both ends.** A connection lives on both maps, so
+  hooking a new map onto a base map also emits the return connection as a
+  patch on that base map, keeping its other directions intact. The return
+  offset is derived, not guessed: all 78 vanilla reciprocal pairs satisfy
+  `back.offset == -offset`.
+- **A Tiled tile is a gen1 block.** Each of the 24 tilesets becomes a Tiled
+  tileset whose tiles are its 32x32 blocks, composited from the 8x8 sheet,
+  so a tile layer *is* the map's `blocks` array. Warps, signs and objects
+  sit on the 16px cell grid in object layers, which is the grid the engine
+  addresses them on.
+- **Collision is visible.** View > Show Tile Collision Shapes draws the real
+  walkability: a rectangle covers each cell whose feet tile is not in the
+  tileset's `walkable` list, which is the rule `src/world/Map.lua` applies.
+- **Maps are shown in their real colors.** Each map is atlased in the SGB
+  palette it renders with, so Cerulean is blue and Lavender is purple in the
+  editor exactly as in game. Vanilla resolves that through a cascade with
+  interiors inheriting the last outdoor map, so the workspace mirrors the
+  cascade and walks the warp graph to colour interiors. Changing a map's
+  `palette` exports `palette = "..."` on the record, which beats the cascade,
+  and the editor offers the real palette names as a dropdown.
+- **New blocks and new tilesets.** `blocksets/*.tmj` show a tileset's blocks
+  as raw 8x8 tiles, four by four, so new blocks can be composed there;
+  per-tile flags on `tilesets/tiles_*.tsj` become `walkable`, `waterTiles`,
+  `doorTiles` and the rest.
+- **Export is a diff, not a fork of the data.** The `gen1-mod-export`
+  extension (shipped in `tiled_gen1recomp`) writes either one map file or a whole
+  loadable mod folder. An edited vanilla map diffs against the imported data
+  and emits `mod.content.maps:patch` carrying *only* the fields that moved, so
+  a mod covers the parts it changes and leaves the rest to the base game; a
+  new map gets `:register` at an index of 1000 or above. An unchanged map
+  exports nothing at all. Exports pass `tools/modkit.py validate` and `lint`.
+- **Or the whole record, on request.** Ticking `exactExport` on a map switches
+  it to `mod.content.maps:override`, pinning the map to exactly what the
+  editor shows. It is off by default because an override wins outright over
+  any other mod patching that map, where a patch composes.
+
+No ROM-derived art travels into an exported mod: a tileset still drawing on
+the player's own imported sheet references that path rather than shipping the
+pixels, and only a sheet the author supplied is copied in.