Opening ROOT files in the browser

Firebird can read an EDM4eic or EDM4hep ROOT file straight from your computer, or from a URL, and show its events — no server, no conversion step, no upload.

Using the panel

1. Press the folder button in the top bar. The data selector drops down, open on the Manual tab (or on Presets when a preset is loaded).
2. In the Events field, pick Upload and drop a .root file on the zone (or click it to choose one), or stay on Select and paste a https:// URL. The Geometry field works the same way for a TGeo file.
3. Firebird looks inside every .root file: a detector geometry dropped into the Events field moves to the Geometry field, with a note.
4. A ROOT event file reports its data model (edm4eic or edm4hep) and how many events it holds, and shows the Events range and Convert group inputs under the field.
5. Type which events you want and press Show.

The Events range takes a single number, a list, or a range — 3, 0,2,4-5, 10-19. Everything you ask for lands in the event selector in the toolbar, so the usual next/previous controls step through them. Events the file does not hold are skipped, and one warning in the browser console lists them: 0-99 on a 10-event file converts events 0-9. A range with no event in the file fails with a message that names the file's event count. One request may name at most 1000 events. pyrobird applies the same rules to the files it converts and logs the warning on the server.

The Convert checkboxes choose which collection groups the conversion produces — tracker hits, tracks, MC particles. They list what the opened file's data model offers, and all groups start on. Unchecking a group leaves it out of the converted event; press Show again to re-convert with a different choice.

A DEX file (.firebird.json, .firebird.zip) loads all its events when you press Show; there is nothing to pick.

The other tabs of the same panel, Presets and Physics, offer the datasets the installation lists; see the data catalog for how those lists are made.

Deep links

?dex= accepts a ROOT URL, so a link can carry a whole view:

/display?geometry=epic://tgeo/epic_craterlake.root
        &dex=https://example.org/reco.edm4eic.root
        &config.events.rootEventRange=0-4

config.events.rootEventRange chooses the events, exactly like the panel's Events box. config.events.rootCollections chooses the collection groups, exactly like the panel's Convert checkboxes — a comma-separated list such as tracker_hits,mc_particles; leave it out (or empty) for all groups. The URL must be reachable by your browser and its server must answer HTTP Range requests — which is how only the needed bytes are fetched.

The file is not uploaded, and not even fully read

A local file never leaves your computer, and Firebird does not load it into memory either: it reads the file's directory and tree structure once, and after that only the compressed blocks that hold the events you asked for. Converting one event of the reference test files costs 20–30 kB of reading. Multi-GB files work the same way as small ones, over a URL just as much as from disk.

That means the cost of "show event 5000" does not grow with the size of the file.

Which converter runs

Source	Converted by
A file you picked or dropped	your browser
http(s)://…/file.root	your browser (HTTP Range)
root://… (XRootD)	pyrobird, which opens the remote file and converts
A path served by pyrobird	pyrobird

XRootD access is unchanged: those URLs go to the server exactly as before. If you would rather always convert server-side, set events.rootConverter to server.

What you get

The conversion is the same one pyrobird convert performs, so the picture is the same whether the file went through the Python CLI or through the browser:

• EDM4eic — every TrackerHitData collection becomes a box-hit piece (box size from the hit's position error), and CentralTrackSegments becomes trajectories with their track parameters.
• EDM4hep — every SimTrackerHitData collection becomes a box-hit piece with a fixed box size (simulation hits carry no errors), plus MC-truth trajectories that connect each particle's hits in time order. The collections listed in config.events.trajectoryExcludedCollections show as hits but stay out of the trajectories. List the Cherenkov and PID collections there: their photon hits are attributed to the charged particle that emitted them and draw zigzags across the photosensors. The ePIC pack lists DIRCBarHits, DRICHHits and PFRICHHits, the same list pyrobird excludes by default.
• MC particles (both models) — every particle of the MCParticles collection becomes a straight line from its vertex to its endpoint, with points on a fixed time grid so the time animation reveals each line at the particle's real speed (computed from its momentum and mass). Nothing is filtered: the line count equals the collection size, and the trajectory id equals the MCParticle index. The piece converts by default but starts hidden — open the left panel (Physics tree) and press the eye on the MCParticles row to show it. A deep link can show it too: config.painters.byPiece.MCParticles.visible=true.

For pieces with tens of thousands of trajectories (background frames), select the batched painter in the right-pane painter panel — or with config.painters.byPiece.MCParticles=trajectory-lines-batched — which draws the whole piece in two draw calls instead of one object per trajectory. All tracks then share one line width and dash pattern; coloring, time animation, and click selection work as usual.

Limits

• One file at a time; opening another replaces it.
• A remote file needs a server that answers Range requests and allows cross-origin reads. Without that, use a root:// URL through pyrobird, or convert ahead of time with pyrobird convert (see Pyrobird).