How Objects Work in Sims 1
Pre-rendered sprites in an IFF container – very different from later Sims games
In The Sims 1, every object on a lot – chairs, lamps, fridges, plants, the pink flamingo – is a single .iff file. That one file holds everything the game needs to display the object and make it do things.
Unlike The Sims 2 and later, Sims 1 objects are not rendered in real-time 3D. What you see on the lot are flat, pre-rendered sprites: images drawn from fixed isometric angles, at each of the three zoom levels, for each of the four camera rotations. The game just picks the right sprite to draw based on how the camera is oriented.
What lives inside an IFF
An IFF file is a container. Inside, it carries several resources, each handling one piece of the object. The ones you will touch most:
- SPR2 – the game-view sprites (what you see on the lot)
- BMP_ – the catalogue thumbnail and speech-bubble images
- OBJD – the master record: price, catalogue category, GUID, and pointers to everything else
- BHAV – SimAntics scripts that control behaviour
- BCON – tunable numeric values (skill gain rate, motive effects, etc.)
- TTAB and TTAs – the pie menu options and their text labels
You do not need to understand every resource type to make CC. Retexturing only touches sprites and the catalogue thumbnail. Creating new objects adds rendering new sprites and generating a fresh OBJD. Only full hacking goes into BHAV, BCON, and TTAB. For a full reference, see the File Reference.
Tools You Need
Which tools matter depends on which route you take
Before any Maxis-era tool runs on the Legacy Collection, you need the registry entries set up. The classic HKEY_LOCAL_MACHINE\SOFTWARE\Maxis\The Sims key is not created by the Legacy installer. The easiest fix is the Feraligatr installer, which also bundles most of the tools below.
A full tool list with every download link is on the Tools page.
Two Routes to Custom Objects
Choose the approach that matches what you want to make
There are two fundamentally different ways to create custom objects, depending on whether you want to change how an existing object looks or build something new from the ground up. Both are covered in their own dedicated guide pages.
Single-Tile vs Multi-Tile Objects
One concept worth knowing before you start
Most Sims 1 objects occupy a single floor tile – a chair, a lamp, a plant pot. Some span several tiles: double beds, dining tables, sofas, the foosball table. Multi-tile objects are more complex internally because each tile needs its own entry in the IFF.
The File Reference OBJD card explains the master-plus-per-tile structure in more detail.
Common Mistakes
| Problem | Cause | Fix |
|---|---|---|
| Game file corrupted after editing | Edited the original IFF in GameData\Objects\ or inside a FAR archive instead of cloning first. | Always clone with TMog before editing. Reinstall the game or restore from a backup to recover. |
| Save corrupted after a tool change | Edited or moved mod files while the game was still running. | Close the game before changing any files. Relaunch to test. |
| GUID conflicts when sharing CC | Used Magic Cookie 0 for public CC. Two creators using 0 can produce the same GUID. | Get your own Magic Cookie from the Magic Cookie Database and use it for everything you share. |
| Catalogue still shows the Maxis name | Name and Description fields were not updated in TMog after cloning. | In TMog, select your clone and edit the Name and Description in the right-hand panel. Use the CC convention: Made by [Handle] – [contact]. |
| Buy Mode shows the original thumbnail | TMog updates the in-game sprites but not the catalogue thumbnail. The original BMP_ resource is untouched. | Open the clone in IFF Pencil 2, right-click the BMP_ Catalog entry (usually ID 2000) → Import → your new thumbnail. |
| TMog will not re-import painted sprites | Sprites were saved as PNG or JPG instead of BMP, or the filenames were changed. | Save out of your image editor as .bmp with the original filenames. TMog matches them up via the export XML. |