Project Files

Project Files (.4hu)

Saving your work writes a .4hu file — a single, self-contained bundle that captures everything needed to reopen the project exactly as you left it, on either platform.

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What's inside

A .4hu is a ZIP archive (binary — don't try to open it in a text editor). Its entries:

Entry	Contents
state.json	The full project state (see below)
mesh.obj	The source mesh, embedded so the original file isn't needed
texture.<ext>	Legacy / single fallback texture (optional)
texture_<matId>.<ext>	One embedded image per material, keyed by material ID

Because the mesh and textures are embedded, a .4hu is portable — you can move or share it without dragging along the original .obj and image files.

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What state.json stores

The project state (currently version 2) records everything layered on top of the raw mesh:

• Import transform — ScaleMmPerUnit, MirrorX
• Page layout — paper size (Name, WidthMm, HeightMm), PagesWide, PagesTall
• Edge overrides — your manual fold ↔ cut toggles, keyed by mesh edge ID
• Flap overrides — per-edge FlapMode (+ the "this side" face), keyed by mesh edge ID
• Piece layouts — per-piece PositionX/Y, Rotation, and group membership (GroupId, UserGroupId) so your arrangement and groupings are preserved
• Texture bookkeeping — which material maps to which embedded image, and their extensions
• Warnings — any non-fatal notes recorded while loading

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Cross-platform

A .4hu saved on Windows opens on macOS and vice-versa — the bundle format and state.json schema are shared. This is the intended way to move a project between the two apps.

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Legacy .pmc

The same project state can also be saved as a plain-JSON .pmc file. Unlike .4hu, a .pmc does not embed the mesh or textures — it only references their paths, so it breaks if those files move. Prefer .4hu for anything you want to keep or share.

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Source

Windows: FourHUnfolder.Application/ProjectSerializer.cs, ProjectState.cs · macOS: Sources/FourHUnfolderCore/Services/ProjectSerializer.swift