ifcurl

ifcurl is a URL scheme, tools, and server integration for addressing shareable views of IFC building models stored in git repositories.

ifc://github.com/brunopostle/simple-ifc@heads/main?path=building.ifc&selector=IfcWall&fov=60

An ifc:// URL encodes everything needed to reproduce a specific model view: the git source, the file, which elements to show, and the camera position. Like a permalink for BIM — paste it, share it, embed it in documentation.

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Architecture

Four interlocking components:

Component	Language	What it does
Python library + CLI	Python	Parse ifc:// URLs, fetch IFC from git, render PNG
Preview service	Python	HTTP server — PNGs on demand
Forgejo integration	Go + assets	Inline markdown previews, "View in 3D" button
Browser viewer	JavaScript	Interactive WebGL viewer, served as a Forgejo asset

Markdown source:
  [Section cut](ifc://host/org/repo@heads/main?path=building.ifc&clip=0,0,3,0,0,-1)
                                      │
Forgejo renders (via Go patch):        │
  <figure>                             │
    <img src="/preview?url=..."> ──────┤── preview service renders PNG
    <a href="/assets/viewer.html?url=…">   browser viewer (WebGL, interactive)
  </figure>

The viewer is also reachable directly — paste or type an ifc:// URL into its toolbar, or drag one onto the page.

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ifc:// URL scheme

Full specification: SPECIFICATION.md

ifc://[user@]host/org/repo@<ref>?<parameters>

Transport is inferred from the URL structure — no prefix needed:

URL form	Transport
ifc://host/org/repo	HTTPS
ifc://git@host/org/repo	SSH
ifc:///path/to/repo	Local file

Refs follow git namespace form to avoid branch/tag ambiguity:

Form	Meaning
@heads/main	Branch tip
@tags/v1.2	Tag
@abc123def	Commit hash
@HEAD	Default branch

Key query parameters:

Parameter	Description
path=	IFC file path within the repository
selector=IfcWall	IfcOpenShell selector — filter elements; + for union
camera=px,py,pz,dx,dy,dz,ux,uy,uz	Camera position, direction, up in IFC world coordinates
fov=60	Perspective field of view in degrees
scale=50	Orthographic view-to-world scale
clip=px,py,pz,nx,ny,nz	Clipping plane — point + normal in IFC coords (repeatable)
visibility=	highlight · ghost · isolate

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Python library and CLI

Fetch an IFC file from a git repository and render it to PNG.

pip install "ifcurl[render]"
ifcurl render "ifc://github.com/brunopostle/simple-ifc@heads/main?path=_test_simple.ifc"
ifcurl render "ifc://..." -o output.png

Use as a library:

import ifcopenshell
from ifcurl import IfcUrl, fetch_ifc
from ifcurl.render import render

url = IfcUrl.parse(
    "ifc://example.com/org/repo@heads/main"
    "?path=models/building.ifc&selector=IfcWall&visibility=ghost"
)
hexsha, ifc_bytes = fetch_ifc(url)   # hexsha is stable even for mutable refs
model = ifcopenshell.file.from_string(ifc_bytes.decode())

png = render(model, selector=url.selector, clips=url.clips or None,
             camera=url.camera, fov=url.fov, visibility=url.visibility)

Remote repositories are cloned as bare repos to the OS cache directory (~/.cache/ifcurl/ on Linux) on first use. Mutable refs (@heads/, @HEAD) trigger a git fetch; immutable refs (commit hashes, tags) use the cache as-is.

For private repositories, configure tokens per host in ~/.config/ifcurl/tokens.json:

{ "hosts": { "github.com": "ghp_…", "gitlab.example.com": "glpat_…" } }

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Preview service

An HTTP service that renders ifc:// URLs to PNG, intended for co-location with a Forgejo/Gitea instance.

pip install "ifcurl[service]"
ifcurl serve --allowed-hosts git.example.com     # restrict to your Forgejo host
ifcurl serve --host 0.0.0.0 --port 9000 --allowed-hosts git.example.com

Pass --allowed-hosts as a comma-separated list of hostnames (with optional :port) the service is allowed to fetch from. This prevents the preview endpoint from being used to reach internal services. Omitting it allows all non-private remote hosts.

Endpoints

Endpoint	Description
POST /preview	Render an ifc:// URL to PNG
GET /preview?url=ifc://…	Same, via query string (used by Forgejo <img> tags)
POST /bcf	Generate a BCF 2.1 zip from an ifc:// URL viewpoint

Caching

Tier	Key	Contents	Notes
2	commit hash + path	IFC bytes	In-memory LRU
3	commit hash + path + selector	Resolved element set	In-memory LRU
4	SHA-256 of full URL	Rendered PNG	Filesystem; immutable refs only

Tier 4 is never written for mutable refs (@heads/, @HEAD).

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Forgejo integration

A source patch for Forgejo that adds:

• Inline markdown preview — [label](ifc://…) and bare ifc://… in markdown render as <figure> preview images linked to the browser viewer.
• "View in 3D" button — appears on .ifc file view pages alongside Raw / Permalink / History.
• Browser viewer asset — viewer.html + viewer-url.js served at /assets/viewer.html.

See forgejo/README.md for full apply, build, and deployment instructions.

Quick summary

# Apply the Go source patch
cp forgejo/modules/markup/markdown/ifc_url{,_test}.go /path/to/forgejo/modules/markup/markdown/
cd /path/to/forgejo && git apply /path/to/ifcurl/forgejo/go.patch

# Build Forgejo
go build -tags 'sqlite sqlite_unlock_notify' \
  -ldflags "-X 'forgejo.org/modules/setting.StaticRootPath=/usr/share/forgejo'" \
  -o forgejo . && sudo cp forgejo /usr/bin/forgejo

# Deploy assets (no rebuild needed)
sudo cp forgejo/custom/public/assets/viewer*.* /etc/forgejo/public/assets/
sudo cp forgejo/templates/custom/footer.tmpl /var/lib/forgejo/custom/templates/custom/
sudo systemctl restart forgejo

# Install and start preview service as a systemd unit
sudo cp forgejo/server-config/ifcurl-preview.service /etc/systemd/system/
# edit ExecStart --allowed-hosts to match your Forgejo hostname, then:
sudo systemctl enable --now ifcurl-preview

Add to /etc/forgejo/conf/app.ini:

[ifcurl]
PREVIEW_SERVICE_URL = http://localhost:8000
; Optional: Forgejo API token for a read-only machine user.
; The preview service will use this token to fetch IFC files from private
; repositories on this Forgejo instance.  The token is appended as a query
; parameter in the <img src> URL generated by the markdown extension, so it
; is visible in page source.  Only set this on trusted private instances.
; SERVICE_TOKEN = <forgejo-api-token>

Private repositories: for the preview service to access private repos on this Forgejo instance, create a machine user with read access and set SERVICE_TOKEN to its API token. The service will use this token when fetching IFC files server-side. Alternatively, configure the preview service's own credentials in ~/.config/ifcurl/tokens.json under the service user account — the service already reads host tokens from that file on startup.

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Browser viewer

A self-contained WebGL IFC viewer (viewer.html) built on @thatopen/components. No build step — loads dependencies from CDN.

Features:

• Toolbar with raw ifc:// URL input and structured fields (repo, ref, path, selector) — editing any field reloads the model
• Selector filtering — IfcWall, IfcWall+IfcSlab (type-name union only in the browser viewer; full IfcOpenShell attribute/property filters are applied server-side by the preview service and are reflected in the URL but not applied visually in the viewer)
• Clipping planes — ✂ clip button, double-click on model surface to place; drag handles to adjust; planes serialised back into the URL
• FOV control, camera sync — the URL in the browser bar always reflects the current view and is shareable
• Drag-and-drop ifc:// URLs onto the page
• Click to identify — click any element to see its IFC type, name, and GlobalId in a side panel; copy GlobalId to clipboard for use in selectors
• ⎘ copy button — copies the current ifc:// URL to clipboard
• Issue button — opens a new issue on the git host with the ifc:// URL pre-filled in the body (works for Forgejo, GitHub, GitLab)
• BCF export — exports the current view (camera, clipping planes, selected elements) as a BCF 2.1 file for import into Revit, Navisworks, etc.
• Download progress — shows percentage or MB while fetching large IFC files

Collaboration workflow

ifc:// URLs function as view permalinks that can be embedded anywhere: Forgejo issues and comments, pull request discussions, markdown documentation, Slack, or email.

Basic flow:

1. Open the viewer and navigate to the view you want to share
2. Add clipping planes or a selector to isolate the relevant geometry
3. Click ⎘ to copy the ifc:// URL, or Issue to open a pre-filled issue
4. Paste the URL into a Forgejo issue, PR comment, or any markdown file — Forgejo will render it inline as a linked preview image

Referencing specific elements:

Click any element to see its GlobalId. Copy the GlobalId and paste it directly as the selector= value — a bare 22-character GlobalId selects that one element (e.g., selector=325Q7Fhnf67OZC$$r43uzK). Use visibility=highlight, ghost, or isolate to control how the selection is displayed.

BCF export for external tools:

Use the BCF button to export a BCF 2.1 file. The resulting .bcf can be attached to a Forgejo issue as a file, or imported into Revit, Navisworks, Solibri, or any BCF-compatible tool to communicate the exact viewpoint and element selection to contractors or consultants using proprietary software.

Authentication

When the viewer is served from the same Forgejo instance (https://git.example.com/assets/viewer.html), it shares the browser session cookie. Any IFC file that the logged-in user can access on that Forgejo instance loads without extra configuration — private repositories work automatically for authenticated users.

IFC files hosted on other platforms (GitHub, GitLab, a different Forgejo instance) are fetched directly from the browser. Only public repositories work for external hosts; there is currently no authentication path for external private repositories in the browser viewer.

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Development

git clone https://github.com/brunopostle/ifcurl
cd ifcurl
pip install -e ".[service]"

# Python tests
python -m pytest tests/

# JavaScript tests (Node 18+)
node --test tests/test_viewer_url.mjs

# Go tests (requires Forgejo source tree with patch applied)
cd /path/to/forgejo
go test ./modules/markup/markdown/ -run TestIfcURL -v

Roadmap

Phase	Status	Description
1 — Python core	✓ done	URL parsing, git fetch, render
2 — Preview service	✓ done	HTTP service with caching
3 — Forgejo integration	✓ done	Go patch, viewer, markdown extension
4 — Bonsai integration	planned	Protocol handler + "Copy view URL"
5 — IFC Viewer integration	planned	Plugin for the open-source IFC Viewer
6 — Federation	planned	IFCDOCUMENTREFERENCE cross-repo links

Development tasks are tracked with beads: bd ready.

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Licence

LGPL-3.0-or-later