Checkpoints

Run Hack Night checkpoints from the browser. Hackers join a queue from their seats. When it's their turn they walk up and press Start presenting, and their screen goes on the projector. It turns off on its own after two minutes. Nobody plugs in a cable.

This guide is for the organizer running a checkpoint night. Developers: see docs/DEVELOPMENT.md.

What you need

• The site URL and a Purdue Hackers ID with the organizer role. Ask an ID admin to give you the role at id.purduehackers.com.
• A projector laptop running Chrome or Edge, plugged into the projector and speakers.
• Optionally, a second laptop for yourself to run the queue. You can also run everything from the projector laptop.

There are three pages:

Page	Who uses it
/	Hackers: join the line and share a screen
/admin	You: run the queue
/host	The projector
/timer	A big countdown for the speaker (optional second screen)

Preview deployments with ID_ISSUER unset show a password form on /admin; use 123456.

Before the night (5 minutes)

1. On the projector laptop, open /host. Click Fullscreen. The click also lets the page play sound.
2. Open /admin and sign in with Purdue Hackers, on your own laptop.
3. Click Start checkpoint. The projector now shows the join address and the line. The first person to join is up automatically.

Running the queue

Hackers open the site, enter their name and project, and click Join queue. They can share their screen while they wait, but they don't have to. You see everyone in the list on /admin.

For each presenter:

1. Check the Preview panel. It automatically shows whoever is next, so you can catch the wrong window before the room sees it. Click Preview on any row to look at someone else. Click follow next to go back to following the line.
2. The first person in line is up automatically. Their page turns green and the projector tells them to walk up. The person after them sees their page flash yellow.
3. They press Start presenting at the podium. If they aren't sharing yet, that one button opens the share picker and starts as soon as they pick a screen. The clock only starts then, never while they're walking up.
4. A small timer stays on screen and turns red for the last 30 seconds. The slot ends by itself at the time limit. They can also click End my checkpoint when they finish early.
5. The next person is up automatically as soon as a slot ends. If the person who is up isn't ready, click Skip on the current card: they go back one place and the next person is up.

Controls

Control	What it does
Start timer	Starts the called person's time for them. Only use it if they can't press Start presenting themselves
Stop	Ends the current presenter now and the next person is up. Clicking it twice never ends the next person too
Pause / Resume	Freezes the presenter's timer. The projector shows a grey ⏸ timer
−30s / +30s	Takes away or adds 30 seconds for the current presenter
Skip	In the line: moves someone behind the next person. On the current card (before they start): sends a not-ready person back one place and the next person is up
▲ / ▼	Moves someone up or down the line
Remove	Takes someone out of the line (if they are on stage, the next person is called)
Limit (s)	Time per presenter in seconds (default 120). Applies to the next presenter
Quality	Stream bitrate: 720p, 1080p (default), 1440p or Source. Lower it if the stream is choppy. Changes the live stream without restarting it
Projector sound	Turns the presenter's sound on the projector on or off
End checkpoints	Closes the line for the night

The row under each name shows whether that person is sharing, not sharing, stopped or disconnected….

The checkpoint ends by itself (just like End checkpoints) if nobody has /admin open for 5 minutes, or if nothing happens for 10 minutes while nobody is presenting.

What to tell hackers

• Use Chrome or Edge on a laptop. Phones and iPads can join the line too, but they share their camera instead of a screen (handy for showing off hardware). Start presenting opens the back camera, Flip camera switches to the front one, and no microphone sound is sent, so a phone near the speakers can't cause feedback. Firefox and Safari can share a screen but not sound. Brave, Opera and Arc work like Chrome. The page needs a recent browser (Chrome/Edge 111+, Firefox 128+, Safari 16.4+).
• The share picker starts on Entire screen. For sound, share a Chrome tab instead and tick "Share audio" (on a Mac, an entire screen can't share sound). Sound only plays on the projector while they're live.
• On Linux, if sharing a screen or window fails or goes black, share a browser tab instead.
• Don't open the projector page on your own laptop.
• Keep the page open. Refreshing is fine. Closing the tab takes you out of the line after 5 seconds (the browser asks first). While those 5 seconds run, the projector shows "disconnected…".

When something goes wrong

Problem	Fix
No sound on the projector	Check that Projector sound is On. Click Fullscreen on the projector once. Then check that the presenter ticked "Share audio"
Someone shared the wrong window	They click Change window on their page. They keep their spot
A presenter isn't ready	Click Skip on the current card. They keep a place just behind the next person
The stream is choppy	Click Stats for nerds, or right-click anywhere on the page. If limited by says bandwidth, lower Quality. If it says cpu, have the presenter close other apps or lower Quality
A "reconnecting…" badge stays on	Check the network connection. The page reconnects by itself
The line is full of fake names	Click End checkpoints, then Start checkpoint. This starts a fresh, empty line
A hacker's share fails with an error name in brackets, like (NotReadableError)	Have them click Try basic share. If that fails too, share a browser tab. Screenshot the error and send it to the devs
A share still won't work	Have them press Present without sharing to talk without a share, or you press Start timer for them. Last resort: plug their laptop into the projector over HDMI
/admin says your account isn't an organizer	Ask an ID admin for the organizer role, then click Sign out and sign in again. Role changes apply at the next sign-in

For other sites and bots

Want to know if a checkpoint is on? GET /api/info is public and returns {"active": true} while a checkpoint is open (an organizer started one and it hasn't ended or ended by itself), otherwise {"active": false}:

curl https://checkpoints.purduehackers.com/api/info

Any site can call it (CORS is open) and the answer is never cached. It is rate-limited per IP like the rest of the site, so polling every 10–30 seconds is fine. It shows nothing else: no names, no line.

Keeping it safe

• Production uses Purdue Hackers ID organizers to run the queue. Taking the role away in ID applies at that person's next sign-in. Sessions last 12 hours.
• Anyone can join the line from a new browser. Hackers don't sign in. Use Remove for anyone who shouldn't be there.