Demos & Recordings

Recorded games that play by themselves in the main menu, the demos you record yourself, and the .gdemo files behind both.

Speedy Blupi plays a recorded game when nobody touches the main menu for a while. Galaxy Eggbert does the same: the menu plays ten short demos, recorded input replayed through the normal simulation, so a demo looks and sounds exactly like real play. Players can also record their own demo into any of the ten positions, give it a name, and pass it to other players as a file. This page describes the state as of 2026-11-10.

Done Main-menu demos, recordings, names, export and import (desktop and web). Not verified Android, a physical gamepad, a real touch screen.

The main menu's demos

How a demo starts

• The Demo button, top right of the main menu under Exit, starts the demos at once.
• 40 seconds without input start them too (kDemoIdleSeconds; the original waited 1000 ticks, "about 30 seconds"). The time counts only in the settled main menu of the active window: not in Play, Pause, Setup, the editor, the help panel, a menu fade or the demo positions screen. Any input, mouse movement included, starts the count again.

The ten positions play in turn, and after the last the first plays again. A position whose demo cannot be played is skipped. Each demo lasts 45 to 50 seconds.

While a demo plays, the recorded input drives the ordinary simulation at 60 ticks a second, with picture and sound, and the word "Demo" is shown top left. The demo uses the recording's own profile (hub doors, lives, controls) but your sound, volumes, 3D terrain, 3D effects level and fullscreen setting.

What stops a demo

• A new key, mouse button, mouse wheel turn, gamepad button or touch stops it and returns to the menu. Mouse movement alone does not.
• Whatever was already held when the demo started (the click on Demo, for example) cannot stop it.
• The press that stops a demo never reaches the menu: the menu ignores input until it is released.
• Losing the window's focus stops it.
• A demo shows one mission. Where play would go on to another mission, or into Pause, Win or Lost, that demo ends and the next one starts.

What is frozen and restored

Before a demo starts, the game keeps the player's own state: the saved profile and settings, camera mode, game speed, the cheat toggles (quick, open doors, show secret, compass, debug), the cheat-entry lock, lives and the list of active cheats. Nothing is saved while a demo plays, the resume file is left alone, and all of it is put back when the demo stops. The shipped demos are checked against this: their replay leaves savedata.txt and resume.txt byte for byte as they were.

Recording your own demo

In the original, demos could only be recorded by a trick (see below). Galaxy Eggbert offers it openly:

1. During a campaign mission or a mission of your own galaxy, open Pause. The Record button sits top right. It is not shown in an editor play-test, during a demo or a resume replay.
2. Record shows the ten demo positions. Click the position to record into.
3. The mission restarts from its start at normal speed and is recorded; "REC" is shown top left. You play and the game saves your progress as always.
4. The recording ends when Play is left (Pause, Win, Lost, or the move to another mission) or after ten minutes. The notice "Demo recorded in position N." confirms it.

From then on that position plays your recording instead of its shipped demo. A recording starts with an automatic title such as "Recorded by player A: mission 11".

The demo positions screen

The same screen is reached from Pause's Record button and from the main menu's Demos button (left of Exit). From the menu nothing can be recorded: a click on a position says "A recording is made in a mission: Pause > Record." Each position shows two lines: its name, "Recorded", "Shipped" or "Empty", then "Mission N", "Galaxy N" or "(unplayable)". A recorded position has an Original button under it, which deletes your recording so the shipped demo plays again.

The arrow keys or a gamepad's d-pad choose a button (drawn lit) and A or Enter presses it; in Pause, B leaves the positions. A recording made in a player's galaxy finds its world by its hash in any player's galaxy, on the desktop and on the web. When its world is not there, the position is kept but skipped until the world exists.

The .gdemo file

A demo is a text file holding the same input history as a resume log (ResumeLog: the start state, the random seed and the raw input of every 1/60 s tick) under a header of its own. Shortened, the start of the shipped demo001.gdemo:

GALAXY_DEMO 1
1
"World 1: pillars, mine pits and lifts"
"Nov  8 2026 19:35:31 fnv1a64=17098780557396544612"
9
"Blupi" 5723123326820972394
"Hide trail" 14695981039346656037
...
"objects" 940733633382668234
"worlds3d/world011.vwr" 17476187514555174857
11 3 1 3279155381 14 10 10 -0 0 0 0 0 0 0 1
"soundEnabled=1
...
END 8344386914525136986

Resume files only work with the identical binary. A demo instead names a simulation revision and the hash of its world, so it survives rebuilds but is never replayed into a different game. Before anything of the player's is touched, ParseDemo() and DemoWorldStatus() check the file. A demo that fails is skipped with a log line such as demo ... skipped: its world has changed.

Where the files live

The player's folder is, since 2026-11-10, ~/.local/share/Galaxy Eggbert on Linux (or under $XDG_DATA_HOME), %LOCALAPPDATA%\Galaxy Eggbert on Windows, or the folder given by --user DIR or GALAXY_USER_DIR. The web build keeps everything under /save in the browser's storage (so recordings are in /save/demos/ and survive a page reload); there, Export is a download and Import uses the file picker. Android keeps the files in the app's private storage. A galaxy exported as a .galaxy pack carries the demos recorded in it; see Your Own Galaxy.

For developers: recording and verifying demos

The command-line flags are read in src/GalaxyEggbertCNA/main.cpp:

A developer's recording ends at Escape (a gamepad's Start), at the mission's end, at the autoplay's end, after --demo-ticks, or when the window closes. The F-keys and Tab are left out of the recording. The two scripts wrap this:

# scripted, from an autoplay script, cut after 45 s, under its own Xvfb display
tools/record_demo.sh build-cna-opengl3 Content/demos/demo001.gdemo 11 \
    --autoplay tools/autoplay/world011.txt --demo-ticks 2700 --demo-title "World 1: lifts and mines"

# replay every shipped demo and compare its end state
tools/verify_demos.sh build-cna-opengl3

When a simulation change makes verify_demos.sh report a shipped demo as different, bump kDemoSimulationRevision in DemoReplay.hpp and record every demo again. The CTest cases:

• VerifyDemoReplay: the file format and its compatibility rules, the idle timer, the input that stops a demo, the play order.
• VerifyDemoFiles: every shipped demo parses with the current revision and matches its world's bytes.
• VerifyDemoReplays: runs tools/verify_demos.sh under Xvfb (only where xvfb-run exists; not on Emscripten, Android or Windows).

Verification status (as of 2026-11-10)

• Desktop: verified live under Xvfb: the button, the idle start (40.02 s after the last input), every stop input, the cycle, an 800x480 window and 1280x720 fullscreen, sound, focus loss, player files untouched, recording, replay equal, Original.
• Web (2026-11-09, headless Chrome): the shipped demos replay as recorded; a recording made there survives a reload in /save/demos/; a desktop galaxy recording imported on the web replays equal.
• Not verified: Android; a physical gamepad or touch screen (an SDL virtual gamepad was used).