SM64-Decomp-Rom-Editor

A graphical object placement and collision geometry editor for Super Mario 64 .z64 ROMs built from the SM64 decompilation. It works like Toad's Tool 64 and Quad64, but runs in the browser and has no dependencies.

Features

• Opens .z64 ROMs built from the decomp (US/JP/EU…), plus vanilla dumps in .z64, .v64 or .n64 byte order.
• Finds every level script by scanning for the EXECUTE(0x0E, …) commands that load them. Levels are named from the JUMP_IF(OP_EQ, LEVEL_x, …) table in the main scripts segment. Nothing depends on hard-coded ROM offsets, so shifted or modded decomp builds work too.
• Reads level data compressed with MIO0 (vanilla / older decomp) or Yay0 (newer decomp), or stored uncompressed (COMPRESS=uncomp).
• Object mode: view and edit, per area:
  • placed objects (OBJECT / OBJECT_WITH_ACTS): position, rotation, model ID, behavior, behavior parameter and act mask (set acts to 0 to disable an object),
  • macro objects: preset, yaw, position, behavior parameter,
  • Mario's start position (MARIO_POS),
  • warp nodes, painting warps and instant warps.
• Geometry mode: the area's collision mesh is drawn colored by surface type. Click a triangle to select it and its nearest vertex, then drag the vertex or type new coordinates. You can also change the surface type of a surface group.
• Free-fly 3D camera. Click and drag to place things on the ground plane (Shift+drag changes height). Also includes "drop to ground" and undo/redo.
• Optional: load the decomp build's linker map (build/us/sm64.us.map) to see behavior names (bhvGoomba, …) and to type behavior names instead of addresses.
• Export an area's collision as a Wavefront .obj.
• Save ROM writes edits back in place. Compressed segments are recompressed; if one no longer fits, it is moved to the end of the ROM and its LOAD_* command is updated. The CIC-6102 header checksum is recalculated.

Running

Browsers can't load ES modules from file:// URLs, so the folder has to be served over HTTP. With Node.js 18+:

npm start            # http://127.0.0.1:8064

Any static file server also works (for example python3 -m http.server), and the editor can be hosted on GitHub Pages without changes.

Open the page, click Open ROM (or drag and drop the ROM onto the window), pick a level and an area, and edit. Click Save ROM to download the edited ROM as <name>.edited.z64.

Controls

Action	Input
Look around	Right-drag, or left-drag on empty space
Move camera	W A S D, Q/E down/up, mouse wheel, middle-drag to pan; hold Shift for speed
Select	Left-click in the 3D view or in the outline
Move selection	Left-drag (ground plane), Shift+drag (vertical)
Focus selection / drop to ground	F / G
Undo / redo	Ctrl+Z / Ctrl+Y (or Ctrl+Shift+Z)
Deselect	Esc

How edits are stored

All edits are made in place, so data never has to be resized:

• Objects, Mario's start and warps live in the level script (segment 0x0E). It is stored uncompressed and patched directly.
• Collision and macro objects live in the level data segment (usually 0x07). On save it is decompressed, edited and recompressed in the same format.
• Collision edits keep the data the same size. You can move vertices and change surface types, but switching between a surface type with a "force" parameter and one without is rejected, because that would change the size of every triangle in the group.

Changes to a level are applied to the in-memory ROM when you switch levels or save.

Project layout

index.html            UI shell
server.js             zero-dependency static server (npm start)
src/core/             ROM / level parsing and writing (no DOM, runs in Node too)
  rom.js              byte order handling, checksum
  compression.js      MIO0 / Yay0 codecs
  level.js            level discovery, level script walker, commit/relocation
  entities.js         editable objects, macro objects, warps, Mario start
  collision.js        collision parser/editor, OBJ export
  mapfile.js          GNU ld .map parser for symbol names
  names.js            level, command and surface type names
src/ui/               WebGL renderer, camera math and the editor app
test/                 node:test suite using synthetic ROM fixtures

Tests

npm test

The tests build small synthetic ROMs (see test/fixtures.js), so you don't need a copyrighted ROM to run them.

Limitations / roadmap

• The 3D view shows collision geometry only, not the textured visual (Fast3D display list) geometry.
• Collision special objects (COL_SPECIAL_INIT) are kept as-is but can't be edited yet.
• Adding or removing objects, and importing new level models, would need the level script and data segments to grow. That isn't supported yet.