Farm Invaders

Tl;DR

Space Invaders, except the invaders are flying saucers with enormous windscreens and the defender is a chicken in a space helmet, armed with eggs.

Play here

Longer Explanation [AI recap]

A run opens with a mothership sliding in to demand "Give us the cow now!" in a deep alien voice, the hen squawking back "Never!", the mothership leaving, and the shooting starting. The cow stands on the ground behind her the whole time. If she runs out of lives, a mothership comes down, puts a tractor beam on the cow and takes it, and the cow has just enough time to say "Moooooooooo" on the way up. It is happier the rest of the time: every round the hen clears gets a "Moo".

Round 42 is the last. Clear it and the beaten fleet rises off the screen in tears to a sad trombone, the mothership conceding the cow. Then night falls, and the cow, the hen and a radioactive fox dance round a campfire under the moon, singing Moo Moo Moo — an original tune — a line each: "They came for the cow, and we said moo moo moo. Moo moo moo we said, and they run moooway!" After one time through, the end panel comes up, and the dance and the song carry on behind it until Play again is pressed.

Thirty minutes a visit (built, but switched off for now with BEDTIME.enabled in src/config.ts). Most players are children, so the game keeps screen time short. The clock starts when the page loads, and only reloading the page resets it. For the last ten minutes the HUD shows "Bedtime in 9:59" under the round, turning red for the final minute. When it runs out, the game stops wherever it had got to and it is night: the hen, the cow and a saucer's pilot stand on a hill under the moon and tell the player that's enough for today ("You've played enough for today!", "It's time to go to sleep now.", "Even we aliens go to bed. Goodnight!"). Then they sing a short lullaby, a line each and the last together: "Hush now, close your eyes, the moon is in the sky, the saucers all fly home, goodnight, sleep tight." It loops for as long as the page stays open. There is no button to leave it.

Nobody is ever killed. No saucer blows up or vanishes: whatever hits one — an egg, a loose toy, the gramophone's last chord, a bump with another saucer — leaves it damaged, and it limps off the nearer side, smoking or yolky, and scores once it is gone. The one exception is the black hole, which is more of a wormhole: whatever goes in is sent home.

Hit saucers drop fruit. About one in eight drops a fruit as it goes. It falls to the ground and lies there for five seconds, and the hen gets its points by walking over it: cherry 100, strawberry 300, apple 500, orange 700, banana 1000, and — rarely — pineapple 1500 and watermelon 2000. Nine fruit in ten are worth 1000 or under.

One egg at a time, whatever the round.

An egg does not shoot a saucer down. One that connects bursts across the canopy and blinds the pilot: the saucer drops out of the formation, hangs there reeling for a moment, then banks over and limps off whichever side of the screen is nearer. It scores when it is gone. Toys scattered across the floor absorb anything that hits them — the hen's eggs and the saucers' lasers alike — and no amount of fire wears them down, or leaves a mark on them.

Eggs shoot lasers down. An egg that meets a laser in mid-air takes it out and is spent doing it, so a well-aimed egg is a shield as well as a shot. From round 3 some saucers fire double-width lasers, and from round 6 some fire triple-width ones; each takes that many eggs, and every egg narrows it by one. The mothership's volleys mix them in too, from the same rounds. They grow more common as the rounds go on, but six lasers in ten stay ordinary.

The toys are not nailed down. An egg comes from below, so it punts the toy it hits up into the fleet, and any saucer a loose toy ploughs into is knocked out of the fight. Every one costs the toy a hit point, so a punted teddy bear is worth three or four saucers and no more. Lasers are simply absorbed; they never move a toy, because a toy pushed downwards is cover turning into a hazard the hen cannot dodge.

Every second round is a mothership rather than a fleet. It takes one egg per round number to see off, and the banner says so before the round starts. It answers with a volley of two directions fewer than the round number and then halved, fired at a third of the rate it started at — it is also the only thing out there that shoots at an angle, since rank-and-file saucers only ever fire straight down. Every five to ten seconds it runs a windscreen wiper across its canopy, clearing about a fifth of the egg on it — picked at random — and every egg it clears is a hit point back. It needs three eggs up there before a fifth comes to one, so a barely touched mothership never bothers.

Watch out for radioactive foxes. Now and then a saucer in the front rank — or, on its rounds, the mothership — drops a glowing green fox instead of firing. It is rare early on, about one every 26 seconds in round 1, and grows steadily more common, reaching one every 7 seconds by round 20. There are never more than four in a round. Eggs go straight through it, toys do not stop it and the black hole does not take it. It falls to the ground and sits where it lands, for a second in round 1 and up to ten seconds from round 19. Then it runs off the side away from the hen. If it touches her she loses a life. The shield is the one thing that keeps it off her, and it breaks doing so. Motherships drop foxes too, out of their belly, on the same schedule as the fleet.

When the hen loses a life she lets out a "buk-buk-BAWK!", a handful of feathers come off her, and she lies dizzy on her side for a second, stars circling her head, before she gets up. When the last hen goes down she stays down, dizzy, while the cow is taken.

A tenth of every fleet deserts. Somewhere in each round, one saucer in ten decides it has had enough, says make ❤️ not war and flies home. They leave unscored: talking somebody out of a fight is not the same as winning it.

Every other deserter drops a shield on its way out — the heart's deserters too. It falls to the ground and lies there for four seconds; the hen gets it by walking over it, or by standing where it lands. The shield takes three hits and does not run out with time: a double laser counts as two hits and a triple as three. A fox touching her breaks it outright, however many hits it had left, and gives her a moment to get past. It grows fainter with every hit, and the HUD shows what it has left. Picking up another tops it back up. It runs alongside whatever upgrade she is holding.

Every 4000 points is another hen, awarded for each threshold crossed rather than one per payout, so a single screen-clearing upgrade can hand back two.

On about one round in six, Einstein turns up, says time freeze mate, and stops the board. The hen and everything she has already thrown carry on; saucers, the mothership, lasers, loose toys and the clock on a Rambo egg all stop where they are for five seconds. An egg that lands while time is stopped splatters it all the same; it hangs there reeling until time starts again, and then limps off.

Watch the corners for a Rambo egg. One turns up in a top corner, sits there for ten seconds, and upgrades the hen's eggs if she can hit it before it leaves. Up to round 19 a round brings none or one; rounds 20–29 bring one or two, rounds 30–39 two or three, and so on, the higher number seven rounds in ten. They come one at a time, a few seconds apart. Which upgrade is not up to her:

Upgrade	What it does
Multishot	Every shot becomes a fan of 5–20 eggs, for six seconds.
Super egg	One shot. It bursts at mid-screen and clears the sky outright.
Beam	A continuous beam for six seconds. It burns whatever it touches, and needs one second on the mothership per egg the mothership would have cost.
Exploding heart	One shot. The whole fleet deserts. The mothership declines — "no xmas truce. This aint 1914. I'm da central command!" — and the hen gets a super egg for her trouble.
Gravity waves	Five seconds of expanding rings. Anything a ring washes over loses attitude control and tumbles off at random; two that bump are both damaged and limp away.
Black hole	One shot. It opens at a random spot in the sky and swallows everything but the hen and the cow: every saucer, the mothership, toys, foxes, fruit, shields, the eggs in the air, the stars round it and even the letters of the HUD, which come back when it closes. The cow and the hen only just survive: the cow clings to the edge of the screen, and the hen keeps her feet planted while the rest of her is dragged, stretched and shaking, towards the hole.
Gramophone	One shot. It drifts up playing, and three seconds later its last chord knocks the whole fleet, mothership included, out of the fight.
Cow burp	One shot. The cow lets go a cloud of bubbles that fans out across the whole screen; every saucer a bubble touches is caught inside it and carried off the screen, and the mothership loses a hit point per bubble.
Wingman	Ten seconds of a second, brown hen who walks the ground by herself and throws eggs non-stop. Lasers that reach her are absorbed — she cannot be hurt until the upgrade runs out.

Every upgrade announces itself over the playfield, because which one you have is not something you chose — and every one of them carries a clock, shown in the HUD as a name, the seconds left and a bar that drains, turning red over the last three seconds. The single-shot upgrades are spent by firing them; their clock is how long they can be carried unfired. A new upgrade replaces the one she is holding. While the beam burns, the fire key does nothing: it is not a gun. Only one black hole can be open at a time.

Running it

npm install
npm run dev      # http://localhost:5173/farm-invaders/
npm test         # headless simulation checks
npm run build    # typecheck + production build into dist/

Controls: ← → or A/D to move, Space to throw an egg, M to switch the sound off and on. The speaker button in the bottom right corner does the same, and the choice is remembered in the browser.

On a phone, hold it sideways and put a finger on the field: the hen heads for the spot under it and throws for as long as your finger is down. An upright phone gets a hint to turn it.

Sound

Everything you hear is synthesised in the browser with the Web Audio API — there are no audio files. The theme, Hoedown in Orbit, is an eight-bar chiptune loop written for this game, so it carries no licence or royalty of any kind. Mothership rounds switch to a second original tune, Mothership March: a slower, villainous loop in D minor with an oom-pah tuba, a timpani and a woodblock. Eggs pip as they leave, splat on windscreens, and splat enormously as a super egg; saucers and toys go up with a bang; lasers buzz; the cow moos at every cleared round, burps when told to, and moos at length on its way into the mothership. The hen clucks when she loses a life, a fox arrives with a crackle of Geiger clicks and a yip, the black hole opens with a long swirling fall, and the mothership's wiper squeaks. In the opening exchange the mothership speaks in a ring-modulated growl and the hen answers in chicken. At bedtime the goodnights are said unaccompanied and the lullaby, in a slow 3/4, is sung over a music box. Browsers keep audio off until the page has been clicked or typed at, so the sound starts with the Start button.

Telemetry

The game can report to Dynatrace Real User Monitoring: page loads, JavaScript errors, and two game events — game_started and game_over (score, round, whether sound was muted, and length in seconds). All of it lives in src/telemetry.ts.

It is off unless two things are true:

1. TELEMETRY_ENABLED at the top of src/telemetry.ts is true. This is the kill switch. Set it to false and push, and the next deploy neither loads the Dynatrace agent nor sends anything. The build then drops the telemetry code entirely.
2. The repository variable DT_RUM_SRC (Settings → Secrets and variables → Actions → Variables) holds the agent's script URL from the Dynatrace web application's setup page. The deploy workflow passes it to the build as VITE_DT_RUM_SRC. Unset, the build reports nothing, which is also how local builds, tests and forks behave. Deleting the variable and re-running the deploy is a second way to turn telemetry off, without a commit.

The URL is not a secret. Anyone can read it from the page, and all it lets anyone do is send data into this one application. Restrict the application's beacon origins to https://zerogvt.github.io and cap its sessions in Dynatrace. Never put a Dynatrace API token in this code.

The player has to agree first. The Dynatrace application runs in opt-in mode ("Data-collection and opt-in mode" under the frontend's Settings → Data privacy). In that mode the agent sets no cookies and captures nothing until the page calls dtrum.enable(). When telemetry is live, a small card in the bottom left corner asks the player. Allow calls dtrum.enable(), and No thanks sends nothing. The answer is remembered in the browser, and the card then shrinks to a Stats on / Stats off switch in the same corner, so changing your mind is one click (dtrum.disable() to stop). A player who never answers sends nothing. Keep opt-in mode on: without it the agent would start monitoring before anyone was asked.

What the Dynatrace frontend needs. It must be on the new RUM experience, since sendEvent doesn't exist on RUM Classic. Everything below is under Experience Vitals → Overview → Web → the frontend → Settings:

• Data privacy: "Data-collection and opt-in mode" on. Leave IP masking and "Do Not Track" compliance on, as they are by default.
• Capture properties → Allowed API-reported properties: add game_event, score, round, seconds and muted. Enter the keys without the event_properties. prefix. Any property not on this list is dropped at ingest. The event still arrives, but with those fields empty, so every query filtering on them returns nothing. Adding a key only affects events sent afterwards. Add a key here whenever telemetry.ts starts sending a new field.
• Beacon origins: accept beacons only from https://zerogvt.github.io.
• Cost control: cap or sample sessions.

Checking it works. Open the live game with DevTools on the Network tab. The …_complete.js agent script should load from js-cdn.dynatrace.com with status 200. After Allow and one game, requests to a path starting with rb_ should go to the tenant. Those are the beacons. If the script shows ERR_BLOCKED_BY_CLIENT, the browser refused to fetch it, and Dynatrace never saw the request. The usual causes are an ad blocker, the browser's tracking protection, a DevTools request-blocking rule, or an extension or security tool installed by your organisation. A phone on mobile data is a quick way to rule your own machine out.

The game events land in user.events within a minute or two. RUM events keep their time in start_time, not timestamp:

fetch user.events, from: now() - 24h
| filter isNotNull(event_properties.game_event)
| fields start_time, dt.rum.session.id, event_properties.game_event,
         event_properties.score, event_properties.round,
         event_properties.seconds, event_properties.muted
| sort start_time desc

How far players get:

fetch user.events, from: now() - 7d
| filter event_properties.game_event == "game_over"
| summarize games = count(), avg_score = avg(event_properties.score),
            avg_seconds = avg(event_properties.seconds),
            by: {round = event_properties.round}
| sort round asc

If the first query is empty, check whether the events are arriving at all. characteristics.is_api_reported marks the sendEvent calls:

fetch user.events, from: now() - 24h
| summarize events = count(), by: {characteristics.is_api_reported}

Rows with true mean the events arrive, so it's the property allow-list. No rows at all means the frontend is not writing to user.events. Sessions in user.sessions are only written after about 30 minutes of inactivity, so they lag behind the events.

To remove telemetry completely:

1. Delete src/telemetry.ts.
2. Delete every line in src/main.ts that mentions telemetry (one import, five calls).
3. Delete the telemetry block in tests/simulation.test.ts (its import, and the block that starts // Telemetry.).
4. Delete the env: block under npm run build in .github/workflows/deploy.yml, and the DT_RUM_SRC variable.
5. Delete this section.

npm run build and npm test will then report anything left over.

How it is put together

No game engine and no image files. Plain TypeScript, Canvas 2D, and Vite.

File	What lives there
src/config.ts	Every tunable number. Balancing happens here and nowhere else.
src/game.ts	The whole simulation: marching, splattering, retreats, the mothership, upgrades, collisions, rounds. Touches no DOM, which is why it can be tested headlessly.
src/sprites.ts	Every sprite, drawn with canvas paths at startup. The only file that knows what anything looks like.
src/render.ts	Draws a frame from game state. Never mutates it.
src/ui.ts	Title card, round banner and game-over panel, as real DOM so buttons and the initials field are keyboard-operable.
src/scores.ts	High scores in localStorage.
src/input.ts	Keyboard state.
src/audio.ts	Every sound effect and the theme, synthesised with Web Audio. The only file that knows what anything sounds like.
src/soundToggle.ts	The speaker button and the M key, and remembering the choice.
src/song.ts, src/lullaby.ts	The ending's song and the bedtime lullaby: notes and lyrics, shared by the audio and the speech bubbles.
src/bedtime.ts	The screen-time arithmetic: how long is left, and when to count it down.
src/main.ts	Canvas setup, the frame loop, the screen-time limit, and which event makes which sound.

Design decisions worth knowing

A splattered saucer leaves the formation outright. It stops taking march steps, steers itself, and is skipped by the wall-bounce bounds, the front-line firing check and the invasion check. That last part matters more than it looks: a retreating saucer crossing the side wall would otherwise bounce and drop the entire formation on the hen's head, and one sinking past the line on its way out would end the run. There is a test for each.

It scores when it leaves, not when it is hit. The retreat is the reward animation, and paying out at impact would make the last second of it dead time. The cost is that a round is not cleared until the final saucer is fully out of the view, which is about a second of watching it go.

A second egg into a splattered saucer is wasted. It bursts on a windscreen that is already covered and the saucer is unaffected. With only three eggs allowed in flight, that is the entire cost the retreat delay imposes, and removing it would make the delay purely cosmetic.

The mothership is its own field, not a saucer with a flag. state.boss sits beside state.ufos rather than inside it, because almost nothing a saucer does applies to it: it does not march, does not hold a column, does not die to one egg, and steers itself. Threading a boss: true through the formation code would have meant a special case in every function that walks ufos. What it does share is the retreat, so it reuses UfoState for that and nothing else.

One second of beam equals one egg. The beam takes the mothership down at one hit point per second, so the rule "as many seconds as it would have taken eggs" is arithmetic rather than a second mechanic to keep in step with the first. The beam passes straight through the toys: they are the player's cover, and watching it evaporate under their own upgrade reads as a bug however it is explained.

The super egg spares the toys and the mothership's hit points alike. It clears every saucer and whatever the mothership has left, which makes it wildly strong on a boss round — that is the point of a one-in-sixteen pickup. It leaves the obstacles standing, because the best thing in the game should not also be the thing that strips your cover.

An upgrade survives the round it was won in. Timers keep running across the round break rather than being reset by startRound, so an upgrade picked up in the last second of a round is not confiscated for clearing it. The shield carries over too, with however many hits it has left.

The freeze exempts the hen, not the player. update runs the hen, her shots, her waves and her beam every frame and skips the rest of the board's ticks while state.freeze is set. Advancing lasers had to be split out of advancing her shots for that, which is the only structural cost of the whole feature.

A stopped laser cannot hurt anybody. Collisions between lasers and the hen are skipped for the duration. A frozen laser is a stationary object, and walking into one costing a life would make a gift into a hazard — including the case where time stops with one already sitting on her.

Stopped time is not a free mothership. Eggs still take it one hit point at a time. It cannot shoot back for five seconds, which is reward enough.

Every upgrade has a clock, including the ones that are a single shot. A countdown the player can read is worth more than the words "one shot", which say nothing about how long there is to line the shot up. The hold on a single-shot upgrade is deliberately generous: it exists so the HUD has something to show and so nothing can be carried indefinitely, not to punish anyone for taking aim.

The black hole is a single shot that the hen does not aim. It used to be six seconds of small holes climbing the screen. It is now one hole that opens at a random spot in the sky and takes everything at once, so it is one of the screen-clearers alongside the super egg and the gramophone. What it looks like is the point: every hull caught spirals in, spinning faster and shrinking as it nears the middle, rather than simply vanishing. It keeps pulling while time is stopped, because it is the hen's, and it spares deserters, which are out of the war already, and foxes, which nothing kills.

The cow is scenery, and that is the point. It has no state, no collision box and no hit points — it is drawn at a fixed spot and nothing it says is simulated. All it has to do is be there, so that the opening demand has something to refer to and the closing scene has something to take. Its burp is the one exception, and even that is the hen's upgrade: the simulation only needs to know where its mouth is.

The wingman lives inside the upgrade. Her position and firing clock are fields of the wingman power rather than a second Hen, so she arrives and leaves with it and nothing else has to know about her. Her eggs are flagged, so they do not count against the hen's cap and cannot collect a Rambo egg — which would replace the very upgrade she is part of.

The run is not over when the last hen falls. endGame moves the game into an abduction phase and onGameOver fires when that phase ends, which is what keeps the game-over panel from covering the scene. The board is left exactly as it stopped and dimmed behind it; the whole thing is driven off one age counter, so the simulation counts and the renderer decides what that looks like.

One state for every way off the board. UfoState has a single leaving variant with a reason, rather than separate splattered and deserting kinds. The two share every movement rule — hang in place, turn for the nearer wall, accelerate — and differ only in the sprite, the speech bubble, whether they sink, and whether they score. Two variants would have meant two copies of the exit code drifting apart.

Only the mothership shoots at an angle. Rank-and-file lasers all travel straight down. Lasers still carry a velocity rather than a fixed fall, because the mothership's fanned volleys need it, but nothing else uses it.

Deserters and hearts pay nothing. Score is for saucers the player actually drove off. Everything that leaves of its own accord — a scheduled desertion, or a whole fleet talked out of it by a heart — leaves unscored, which is the price of the heart being the most spectacular thing in the game.

Three upgrades take the mothership outright (super egg, black hole, gramophone), three grind it down (the beam at one hit point per second, gravity waves at one per wave, the burp at one per bubble that lands), the heart is refused, and multishot and the wingman do what they always do. That spread is deliberate: a boss round should sometimes be stolen by a lucky pickup, but three of the nine have to be earned and two are no help beyond the usual.

Lasers travel at half the speed they once did. That has a second effect worth knowing about: a slower shot is on screen for longer, so the cap on lasers in flight bites more often. In round 1, where the cap is two, the fleet gets off about a quarter fewer shots as a result; by round 3 the cap has grown and the interval has shortened enough that it makes no difference.

Difficulty scales on four axes, not one. Each round adds rows (to five), fires lasers more often and faster, allows more of them on screen at once, and starts the formation lower. On top of that the formation accelerates as its ranks thin within a round, so the last saucer is the frightening one. The fleet is six columns by two ranks in round 1, narrower and shallower than it once was, which is the single biggest lever on how hard the early rounds feel.

Cover is spent, not eroded. Nothing that is shot at a toy damages it: eggs, lasers and everything the upgrades fire are all simply absorbed. What stops the player parking behind one for ever is that a toy blocks her own eggs as readily as it blocks the fleet's lasers, so a toy overhead is a wall in both directions. The only way to clear it is to punt it up into the fleet with those same eggs — which costs shots and gives up the cover. That is a decision rather than an erosion, and it replaces the original's crumbling bunkers with a trade.

A wrecked saucer costs the loose toy a hit point, and nothing else does. Those four hit points are no longer a health bar — they are how many saucers a launched toy is worth before it breaks up. Without the cost one egg into a toy would sweep a column clean and the toy would still be climbing.

Toy placement is constrained, not freely random. The usable width is divided into one lane per toy and each toy is jittered inside its own lane. They can therefore never overlap at the start of a round, never touch the walls, and never line up into a barrier that seals off a column. Once they are loose they are free to go anywhere, including through each other — four toys are too few for toy-on-toy collisions to be worth the frame time.

Sprites are drawn in code rather than loaded. Cruder than hand-drawn art, but identical on every platform, nothing to license, and clean and egg-covered canopies can share one hull. Swapping to emoji or PNGs means rewriting src/sprites.ts and nothing else.

Known limits

• Desktop keyboard only. There are no touch controls, so the game is not playable on a phone. Adding them means a second input source writing the same three fields in src/input.ts.
• Sound is synthesised, not recorded. It is chiptune by construction — a splat is filtered noise, a moo is a sawtooth through a vowel filter. Swapping in recorded samples means changing the effect table in src/audio.ts and nothing else.
• High scores are per-browser. They live in localStorage, are not shared between players or devices, and vanish when site data is cleared.
• Einstein cannot be missed, or sought. The visit is on a timer, not a pickup: there is nothing to shoot and nothing to steer towards, so a round either gets one or does not.
• Upgrades are not chosen. Which of the nine a Rambo egg grants is random and cannot be influenced. That is deliberate — being able to plan around it would spoil the joke — but it does mean a run can be decided by a coin flip.
• The obstacles are mostly nursery toys. They are carried over from the previous theme, so a rocking horse and a teddy bear are what shields the hen from orbital laser fire — and, now, what she fires back. A bicycle and a tractor have joined them, and an alien doll; each round draws four of the seven. Replacing them is confined to the toy painters in src/sprites.ts and the ToyKind union.

Deploying to GitHub Pages

.github/workflows/deploy.yml builds and publishes dist/ on every push to main. It assumes this directory is the repository root. Two things must be true before it works:

1. The repository is named farm-invaders, so that base in vite.config.ts matches the URL GitHub Pages serves from (/farm-invaders/). If the repository has a different name, change base to match it.
2. Pages is enabled with Settings → Pages → Source → GitHub Actions.