Lantern

A small GUI for authoring Marp slides on GNOME. Edit on the left, see the slide render on the right, present from the same window.

Named after the magic lantern: the 1600s slide projector that came two centuries before cinema, where a presenter would burn an oil lamp behind painted glass slides and talk, sing or play music to the projected image. Same idea, a bit cooler (sorry).

Standing on shoulders

Lantern doesn't render slides, parse Markdown, draw the window, or export PDFs — other people's software does all of that. Lantern just wires them together behind a GUI.

Sincere thanks to:

• Marp,
• GTK 4,
• libadwaita,
• GtkSourceView,
• WebKitGTK,
• chrome-headless-shell,
• Node.js,
• Flatpak,
• IBM Plex Mono — bundled under the SIL OFL 1.1 for the editor typography, and
• the Lantern icon, adapted (with light modifications) from an illustration by leedanii on Unsplash.

Just want to run it

Each tagged release ships a ready-to-install bundle. Grab nz.ursa.Lantern.flatpak from the latest release, then:

flatpak install --user ~/Downloads/nz.ursa.Lantern.flatpak
flatpak run nz.ursa.Lantern

(You need flatpak itself installed: sudo apt install flatpak on Debian/Ubuntu, similar for other distros.)

Build it yourself

Flatpak. For reproducing what the release ships, or making your own changes.

sudo apt install flatpak-builder
./scripts/build-flatpak.sh
flatpak install --user build/nz.ursa.Lantern.flatpak
flatpak run nz.ursa.Lantern

Local install (for hacking on the Python). HTML export works; PDF/PPTX don't (no bundled Chromium outside the flatpak).

sudo apt install python3-gi gir1.2-gtk-4.0 gir1.2-adw-1 \
                 gir1.2-gtksource-5 gir1.2-webkit-6.0 \
                 nodejs npm flatpak xdg-utils
./scripts/install-local.sh    # ./scripts/uninstall-local.sh to remove

Using it

• New / Open from the welcome screen or burger menu.
• Layout toggle in the header: editor / split / preview.
• Present in window — borderless, keeps current size (good for Zoom).
• Present fullscreen — F5. Escape exits either present mode.
• Export → HTML / PDF / PPTX from the burger menu.
• Autosave is on; no save button.

chrome-headless-shell

The bundled binary is Google's headless Chromium build. For headless render-to-PDF it makes no network calls beyond loading the local HTML marp generated. To swap in ungoogled-chromium, set CHROME_PATH before launch:

CHROME_PATH=/path/to/ungoogled-chromium flatpak run nz.ursa.Lantern

Layout

src/lantern/      Python GTK app
src/lantern.in    Launcher template
data/             Desktop entry, AppStream metainfo, icon
flatpak/          flatpak-builder manifest
scripts/          install-local, uninstall-local, build-flatpak

Status

Open / new / edit / live preview / autosave / two present modes / export to HTML, PDF, PPTX — all working. Not built yet: recent files, settings, presenter notes view, PNG/JPEG export.

License

Copyright © 2026 ursa.nz. Released under the GNU General Public License, version 3.0 or later. See LICENSE for the full text.