MegaDrive Buddies

Thirty-seven Mega Drive characters who live on your macOS desktop. They pace the length of the screen at their own speeds, do the things their games had them do, and when two of them end up near each other they square up and have a go.

They talk, in speech bubbles — about video games, up to 1997, and nothing after. Jokes, facts, passing remarks, and two-handers with whoever is standing nearest. There are no voices: these are 16-bit characters, and a text box is what they had. They also grunt, thud and shout with the sound effects out of their own games.

No network access, no analytics, no bundled anything, no upsell. They are windows that draw a sprite. Quit them from the menu bar and they're gone.

📖 shadi0077.github.io/desktop-buddies

The sibling app in this repository is Desktop Buddies — the same engine with the talking left in: nine Microsoft Agent characters who tell jokes, sing, and argue with each other.

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Build and run

macOS 11 or later on Apple Silicon, plus the Xcode command line tools.

git clone https://github.com/shadi0077/desktop-buddies.git
cd desktop-buddies
./build.sh megadrive-buddies && open "build/MegaDrive Buddies.app"

./build.sh with no argument builds both apps in the repository.

On the artwork. The sprites and sounds belong to Sega, SNK, Capcom, Konami, Interplay, Disney, Marvel and others — community rips of sixteen-bit games. They're included so this runs from a clone, but they are not covered by the MIT licence and are not mine to license — see SPRITES.md. Rights holders: open an issue and it comes down.

There is no Xcode project. build.sh compiles the sources with swiftc, assembles the .app, and ad-hoc signs it. This half of the repository builds in about seven seconds into a thirteen-megabyte app.

The cast

Streets of Rage 2	Axel, Blaze, Max, Skate
Streets of Rage 1	Adam, Axel (1991), Blaze (1991)
Streets of Rage enemies	Galsia, Donovan, Eagle, Slum
Sonic the Hedgehog	Sonic, Tails, Knuckles, Dr. Robotnik, Mecha Sonic, Sonic (3D Blast)
Ristar	Ristar
Platformers	Earthworm Jim, Pulseman, Sparkster, Donald Duck
ToeJam & Earl	ToeJam, Earl
Fighters	Terry Bogard, Ryu, Robert Garcia, Joe Musashi, Gambit, Sketch Turner
Hyperstone Heist	Raphael, Leonardo, Michelangelo, Donatello
Later, same faces	Axel (1994), Sonic (Spinball)
Moonwalker	Michael Jackson

Both Streets of Rage games have an Axel and a Blaze, seven years apart, so the older pair carry the year in the menu; the 3D Blast Sonic is pre-rendered rather than drawn and looks it, which is why he ships alongside the Sonic 2 one rather than instead of him. Have one of them out, or all thirty-seven. Three Axels and four Sonics is a lot of one man and one hedgehog, but the sprites really are different work by different teams in different years, which is most of the interest.

They're told apart by how they move rather than by what they say, because there is nothing to say:

	distance	speed	beat	restlessness
Sonic	1000–3600	420 pt/s	5–12 s	3.6
Pulseman	800–2600	300 pt/s	7–15 s	2.8
Skate	900–3000	300 pt/s	5–11 s	3.4
Blaze	600–2200	190 pt/s	6–14 s	2.6
Axel	600–2200	165 pt/s	7–16 s	2.6
Max	500–1600	120 pt/s	11–24 s	1.6
Dr. Robotnik	300–1100	120 pt/s	10–22 s	1.2
Earl	300–1200	110 pt/s	12–26 s	1.1

Sonic crosses the whole screen and travels on his run cycle, because at 420 points per second a walk cycle reads as a moonwalk. Max is a slow, heavy man who doesn't go far, and Robotnik is slower still. The enemy rips are small — a handful of poses each — so their repertoire is short and their beats are sparse: better a character who stands there convincingly than one who cycles three frames every four seconds.

Sizes are per character too, and deliberately not levelled: a Mega Drive Sonic is 38 pixels tall and Terry Bogard is 92, and pretending otherwise would make a hedgehog the size of a man. They're nudged toward each other, not flattened.

Walking

They walk, so they travel at walking pace and go a long way with it — across the screen, not a hop and a stop. Roaming carries a distance range, a speed in points per second and a restlessness, because a walk cycle played while the window jumps 500 points in half a second reads as moonwalking, which is exactly what it looked like before this existed.

Measured on Axel: 102 position changes over one stretch, 1846 points travelled, largest single step 38 points.

Direction is picked from the room actually available, so somebody parked against an edge never chooses a target that clamps back onto itself, and the travel is eased in and out so a walk starts and stops rather than snapping to full speed.

Squaring up

Two of them within 420 points of each other stop wandering and have a go. It has the shape of a conversation — take turns, face each other, nobody moves while somebody else is mid-swing — with the content physical: one swings, the other blocks or takes it, then counters.

Let Them Fight in the menu walks two of them together first, rather than waiting for the wandering to bring them close.

Facing matters here. Every sprite set faces the viewer's left unmirrored, so turning to face somebody means mirroring — and whoever isn't swinging still turns to watch.

What they talk about

Sixty-four facts, eighty-nine jokes, seventy-two passing remarks and seventy-eight two-handers, all about games up to 1997 and none about anything after, plus a hundred and twenty lines belonging to particular characters. The thinnest character in the cast has seventy-five things it can say before it has to repeat itself, and test.sh holds that number as a floor rather than a target. The cutoff is the point: these are characters who stopped paying attention in 1997, so they talk about arcades, cartridges, the console war and the games that were new to them.

Sonic: I do the whole level in thirty seconds. Knuckles: Then you've seen none of it. Sonic: I've seen it thirty times.

The facts are true. Where a story is famous but the details are argued over, it's phrased as the story it is — in 1997 nobody had dug up the E.T. landfill, so the line says nobody has checked. test.sh enforces the cutoff by scanning every line for a year later than 1997, which is exactly how the two slips in the first draft were found.

Jokes are told properly: setup, a beat to let it land, then the punchline with a flourish. Chattiness in the menu is Quiet, Occasional or Chatty, separate from Liveliness — pacing about and talking are different appetites, and somebody who wants a lively desktop doesn't necessarily want it narrated.

Exchanges are written for pairs where the pairing is funny — Sonic and Knuckles, Ryu and Terry, ToeJam and Earl — and the rest of the pool is unattributed, so any two characters standing near each other have something to say. A test asserts every possible pair has at least five exchanges available, because a pair with nothing to say just stands there.

Every character has at least three lines only they would say — Michelangelo has opinions about nunchaku censorship, Earl declines to hurry, Galsia notes that somebody has to be the first thing you hit, and Donatello knows the bo has the longest reach in the game and that nobody uses it. A test enforces the minimum: shared remarks are about games, and a character with none of its own is a stranger reciting trivia.

There are no voices. The app renders a bubble and nothing else: a synthesiser reading Sonic's lines aloud would be a different, worse app, and these characters never had voices to begin with.

Sound instead of speech

SoundBank plays short one-shots through AVAudioPlayer. Every animation makes a fitting noise, chosen by clip name: specials and celebrations shout, knockdowns thud, everything else grunts.

Five rips, five sound sets, and none of them says what any of its sounds are. The Streets of Rage rip names voice clips V00–V52 and effects 00–49; the Sonic and Ristar rips are numbered by sound-test index, and the ripper says why in his readme — "I did not name any of the sound files by concept (jump, ring, spindash. etc), just by their numbers".

So the grouping is inferred, and from different evidence for each. The Streets of Rage set goes by that naming convention plus duration. The Sonic sets are grouped by measuring the audio: a short burst with no pitch to it is an impact, a sweep that rises is effort — a jump, a spring, a spin-dash winding up — and the bright tonal ones left over are shouts, which is where ring collection lands, exactly where you want it. Measured, the groups come out as distinct as the labels claim:

	impact	effort	shout
Sonic 2	0.45 s, ~610 Hz	0.61 s, ~4330 Hz	0.69 s, ~2410 Hz
Sonic 3 & Knuckles	0.63 s, ~370 Hz	0.66 s, ~2680 Hz	1.15 s, ~1650 Hz

Ristar's rip is his voice and only his voice, so measuring it is pointless — those go by length instead, and his set has no impacts at all. SoundBank falls back to whatever a set does have rather than going quiet at the one moment a noise is called for, and test.sh asserts every kind finds a sound for every character rather than merely that the bank exists.

The rips are 44.1 kHz stereo, which across three sets would have been sixteen megabytes on its own. They ship as 22.05 kHz mono: the Mega Drive's FM chip barely reaches 11 kHz, and none of it was stereo in any meaningful sense.

The characters from games we have no sound rip for stay silent. Borrowing another game's effects for them would be worse than saying nothing — but the fighters share the Streets of Rage set, on the grounds that a grunt suits a man throwing a punch whichever game he came out of.

The rip names voice clips V00–V52 and effects 00–49, with no index of what each one is — nobody wrote down which grunt is which. The grouping is by that naming convention plus duration: short voice clips are exertion, short effects are impacts, longer voice clips are shouts. It's an inference, not a transcription, and it holds up because the categories are coarse.

Volume is theirs alone — a slider in the menu, independent of the system volume. Turning them down doesn't quieten anything else, and turning the Mac up doesn't make them shout.

AVAudioPlayer is deliberate rather than incidental: these want firing and forgetting, and play() returns false on a dead audio device instead of raising the uncatchable ObjC exception AVAudioPlayerNode does.

Feeling alive

A desktop pet is dead the moment you can feel the timer behind it. Four things do most of the work:

Energy. A single 0–1 value that rises when something happens to them and decays back toward a baseline. Everything about the rhythm reads off it — the gap between beats, and which kind of beat gets picked. Lively means shorter gaps and more moving about; winding down means small, still beats and long pauses. Without it every gap is drawn from the same flat distribution and the tempo never changes.

They know whether you're there. CGEventSource.secondsSinceLastEventType gives seconds since the last keyboard or mouse event, needs no permission at all, and is the difference between a pet and a screensaver. Away for three minutes and the baseline drops to 0.12 — they settle rather than performing to an empty room.

They notice the cursor. Come within 250 pt and they turn and point at it; shoot past and they startle. This is edge-triggered on the cursor arriving, not level-triggered on it being nearby — the first version greeted a parked cursor every nine seconds forever, which reads as a stuck loop rather than attention. There's also a speed floor, so a motionless cursor doesn't count as an arrival when it's the character who moved.

They get bored of you. Poke one repeatedly and the reaction decays: startled, then playful, then visibly tiring of it, then nothing at all. Stop for seven seconds and it resets. Paired with a short memory of recent animations, so the same move doesn't come up three pokes running.

Not every beat produces a movement, either. A settle beat is often just standing guard, which is what these characters spend most of their time doing.

Soft-locks worth knowing about

A "bit" — guard then punch, knocked down then back up — owns the animator across its whole intro/loop/outro sequence and hands back through a deferred callback guarded by a generation token. Drop the callback and the character is stranded mid-bit forever. That has genuinely happened twice, so Brain.tick carries a 60-second backstop that returns anyone stuck in .busy to idle.

The third time was the platformer cast arriving. Animator.play only calls back for a clip that finishes, and a looping one never does — which was fine while every flourish was a punch, and stopped being fine the moment Sonic's repertoire included his run cycle and Tails' included flight. The backstop caught it, which is the point of having one: the trace read [sonic] perform walk and then, sixty seconds later, stuck busy for 60s — recovering. Clips now go through Brain.playOnce, which hands back on a timer when the clip loops, so a looping flourish reads as a beat of running on the spot.

Using them

Click	They react
Menu	Say Something, Tell a Joke, Tell Me Something, Let Them Talk
Drag	Pick one up and put it somewhere else
Right-click	Same menu as the menu bar
Menu bar icon	Do Something, Let Them Fight, Do a Trick, Who's Here, volume, per-character controls

Liveliness controls how often they do anything: Calm, Occasional (default), Restless. It scales each character's own pacing rather than replacing it, so Max stays slower than Skate at every setting — test.sh asserts exactly that. Size is Small / Medium / Large. Mute Sounds silences everyone in one click. All of it persists between launches, including who was on screen and where they were standing.

They are non-activating floating panels, so they never steal focus, follow you across Spaces, and sit above normal windows without blocking clicks — only the opaque pixels of the sprite itself take mouse events.

Can't see the menu bar icon?

It's whoever is out, in miniature — 18pt, cut from the sprite sheet. The sheets that have portrait art end with it, and a portrait reads far better at that size than an action frame, which flattens into an unreadable blob.

If it isn't showing at all, something is hiding it rather than failing to create it. Bartender, Ice and similar menu-bar managers hide unrecognised items by default; look in their hidden-items list. macOS also parks items off-screen when the bar is full, which on a notched MacBook happens sooner than you'd expect.

Either way you're never locked out: right-clicking any character opens the same menu. The item sets an autosaveName, so once you place or unhide it, that choice sticks.

Compatibility

macOS 11 Big Sur and later, Apple Silicon — every macOS version that has ever shipped on an Apple Silicon Mac. test.sh asserts the binary's minos and Info.plist agree on 11.0 and that an arm64 slice is present, so this can't regress quietly.

One thing degrades rather than breaks on older systems: Open at Login offers to open Login Items in System Preferences on macOS 11–12, and is a one-click toggle via SMAppService from 13 on. The menu-bar icon is cut from the sprites rather than an SF Symbol, so it looks the same everywhere; the SF Symbol is only a last-resort fallback if the sprites can't be loaded at all.

For Intel Macs as well, build each slice and lipo them together — the sources need no changes.

Cutting the sheets

The rips arrive as one image per character with frames laid out in irregular rows. tools/sheet.py segments it: find horizontal bands of content, then columns within each band, then split each column at its own vertical gaps, then trim every frame to its bounding box. Frames are anchored bottom-centre on a shared canvas so their feet stay planted.

Bands map almost one-to-one onto animations — idle, walk, jab, kick, the Grand Upper, knockdown, and the portrait art at the end. Almost, and the exceptions are the whole job. Three have bitten:

Captions live inside frames. A label printed next to a sprite is part of the same run of content, so it lands in that frame. Those frames are a normal size, so no filter catches them. Blaze's walk starts two frames later than it looks like it should for this reason. I tested whether an unusually-short-frame rule would help; it would have thrown away her projectile and her lying-down poses instead.

A column can hold two sprites. Wherever a sheet packs a short second row, one column of a band contains two stacked sprites — and they come out as a single frame. Galsia shipped like that: a man with a second man growing out of his head. Nothing about the frame's size gives it away. The cutter now splits columns at their own gaps, and test.sh checks every shipped frame holds exactly one sprite, so this particular embarrassment can't come back.

The Streets of Rage 1 rips have no whole-body walk. That game composited a walk from separate torso and leg sprites, so frames 3–10 of each character are disembodied legs. The trio glide on their idle and roam much less, which is better than animating a pair of trousers across the desktop.

Not every sheet has rows. The Hyperstone Heist turtles sit at whatever height suits them, so a band of the sheet spans several sprites at different offsets, the gap between two of them is covered by a third sitting higher, and column projection welds the lot into one frame. sheet.py --blobs segments by connected pixels instead, which doesn't care about rows.

Blobs bring their own trap. A sprite is one blob except where the art has detached parts — a raised sword, the shadow under the feet — so those have to be joined back on, and joining by proximity chains: on a busy sheet every blob is within a few pixels of the next, and Leonardo's entire title area came out as one 636×406 frame. Joining only lopsided pairs fixes that and breaks differently, because beside a 649×335 piece of title art a 40×55 turtle is lopsided too. What works is an absolute rule: a blade, a shadow or a spark is small or thin in its own right, and anything bigger is a sprite.

Sheets annotate themselves, and the annotations are hazards. The Sonic sheets mark "place between other frames" with a green bar, the Knuckles sheet with a pale blue one, and a bar sitting between two cells welds them into one frame — two Sonics, one sprite. Ristar's sheet separates its sections with white rules, and a rule welds a whole row into a single 900-pixel frame. The cutter keys out the three MS Paint marker colours by name, and ignores the pixels of any line running nearly the full width or height of the sheet.

I tried being clever about this first: Mega Drive colours all sit on the hardware's palette grid, so anything off the grid should be an annotation. It reads beautifully and it's wrong — several sheets were saved through a palette that shifted the sprites off the grid too, and the rule quietly keyed out Mecha Sonic's jet flames.

The pipeline, end to end:

./setup.sh sheet galsia ~/Downloads/galsia.png   # cut the sheet, render the index
python3 tools/index.py galsia              # numbered contact sheet — look at it
python3 tools/catalog.py                   # after authoring the ranges

script	what it does
sheet.py	Cuts a sheet into trimmed, anchored frames
index.py	Numbered contact sheet — the only way to author ranges honestly
catalog.py	The hand-authored animation catalogue: clip ranges, fps, loop flags
sounds.py	Groups a sound rip into effort/impact/shout and packs it
icon.py	Builds the app icon from a hero frame
lineup.py	The cast picture at the top of this README

How it works

file	role
SpriteStore.swift	Frame atlas loading, lazy decode, NSCache
BuddyView.swift	Draws a frame, mirrors for direction, pixel-accurate hit testing
Animator.swift	One 60 Hz tick drives both the sprite clock and motion
Brain.swift	Behaviour state machine — idle beats, walking, reactions
Cast.swift	Assembles each character; runs the sparring
Personality.swift	What makes one of them not the other — pace, reach, moves
SoRPersonalities.swift, SonicPersonalities.swift, ArcadePersonalities.swift	The other thirty-six
GameTalk.swift	Everything they say — facts, jokes, remarks, two-handers
SoundBank.swift	The game's sound effects, and which one suits which move
Product.swift	Reads the bundled manifest: the name, and who ships
VolumeSlider.swift	The app's own volume control, in the menu
AppDelegate.swift	Menu bar item, preferences, login item

A product is a JSON manifest in products/ — a name, a bundle identifier and a cast. The build copies only that cast's sprites and stamps the name and bundle id into the app, so shipping a subset (one game, say) is a JSON file rather than a target.

Set BUDDY_DEBUG=1 to trace behaviour decisions on stderr, and BUDDY_TURN=fight to start a scrap on launch rather than waiting:

BUDDY_DEBUG=1 "./build/MegaDrive Buddies.app/Contents/MacOS/MegaDrive Buddies"

[axel] wander from 4694,122 in 0,82 5120x1328
[axel] walkTo (4694,122) -> (3504,90)
[cast] sparring: axel and blaze, 214 pt apart

Tests

./test.sh

Checks the deployment target, that every clip a personality names actually exists, that every shipped frame holds exactly one sprite, the wander target maths (the edge cases are the whole point), the liveliness rules, and the volume slider — then renders every animation headlessly through the real BuddyView into shots/, which is how the sprite work gets eyeballed without needing screen-recording permission.

tools/gamecasttest is the one that catches most mistakes: name a clip a character hasn't got and it says so, rather than the character silently performing nothing. That is exactly how Axel came to be doing cheer — a clip that doesn't exist — for a whole afternoon.

Contributing

See CONTRIBUTING.md — it covers getting it running, the failure modes that have bitten repeatedly, and how to add a character. There is one sheet already cut with nothing authored for it, and it's the interesting one: Dynamite Headdy, whose sheet holds heads and bodies and no complete figure anywhere.

Licence

MIT, for the code. See LICENSE.

Sprites

Axel, Sonic, Ristar, Terry, Jim, the turtles and the rest belong to Sega, SNK, Capcom, Konami, Interplay, Disney, Marvel and others. They are used here as-is and are not mine to license. Fine for personal use — check before shipping this anywhere. See SPRITES.md.

Where this comes from

This repository is generated. The engine, the tools and every character live in shadi0077/desktop-buddies, and tools/publish.py exports this app from it — so a fix to the Brain or the sprite pipeline is made once there rather than three times.

That means changes committed here are lost on the next export. Open issues and pull requests against the shared repository.

Build

./build.sh && open "build/MegaDrive Buddies.app"

macOS 11 or later on Apple Silicon, plus the Xcode command line tools. The sprites are included, so a clone builds and runs directly.