Roll Hippo — user guide

Roll Hippo gives you a roll two ways. Deal a card from a shoe holding every outcome your dice could produce, or throw the dice themselves — you choose the set-up once, then hold the phone upright, shake it, set it down and read what it says. This guide covers every screen, every gesture and every setting.

Getting started

Open the app and you are on the picker. It starts on the default, two white six-sided dice, and any set-ups you have saved are listed as a row of profiles underneath it, so opening one is a single tap rather than a question asked before you can see anything.

The very first launch is the one exception: a short tour runs over the top of the picker, and it is the only thing the app ever puts in front of you unasked. Skip it or finish it and every launch afterwards is the picker, straight away, every time.

There are four screens in all. The picker is where everything is chosen, and it has two pages: a set of dice, or a shoe of cards standing in for one. Whichever page you are on is what the button along the bottom does — it reads Roll or Deal — and it takes you to the screen that matches, the tray or the card table. The fourth is the scanner, which reads someone else's set-up off their screen.

The guided tour

The first time you open Roll Hippo, a short tour runs over the top of the app: seven cards, one idea each. Swipe the card sideways for the next one, or tap Next, or tap any of the dots to jump straight to it. Skip leaves at any point and Done closes the last one.

It is not a slideshow of pictures. Each card is said in front of the screen it is describing — the card page, the dice page, or a tray with dice actually in it — and the one thing it is naming is the only part of that screen left lit. The tray is real, too: on the card about throwing, shaking the phone throws the dice behind it.

Seven cards, in the order you would use the app:

• the two pages — dice and cards — and the swipe between them;
• the rack, and how a die gets its kind and its colour;
• profiles: + New to keep a set-up, and the press-and-hold menu behind every one of them;
• Roll and Deal, and which of the two the button is;
• Throw and Draw, and the shake that does the first of them;
• the separate sets, and the swipe between them in the tray;
• the menu at the top left, and motion control inside it.

Nothing in the tour changes anything. Only the card of words takes taps — the screen behind it is there to be looked at rather than used — and the dice and the shoe it demonstrates with are the tour's own rather than yours. Your saved profiles are the exception, and deliberately: the card about profiles shows the row you actually have. Whatever you had on the picker is exactly where you left it when the tour closes, and no profile is written.

Setting up your dice

The rack at the top of the picker is your set of dice — two rows of five, filled left to right, up to ten.

• Add a die by tapping the large + in the first empty slot.
• Change a die by tapping it. A blue ring in the rack says which one you have hold of, and the editor opens underneath with that die's colour and kind already lit.
• Choose its kind from the row of chips: D4, D6, D8, D10, D12, D20 or Poker.
  Poker is a six-sided die whose faces are the six cards a poker die carries — nine, ten, jack, queen, king and ace — printed as the cards themselves rather than as letters, with the pips laid out the way a card lays them out. In ivory it prints its jack, queen and king in blue, green and red, the way a real one does; painted any other colour it prints in that die's own ink, with the red suits still red.
• Choose its colour from the row of swatches above the chips. Each die carries its own, which is what lets you tell one from another once they are all on the floor of the tray.
• Take one away with Remove, at the right of the editor's heading.

When the rack says what you want it to say, tap Roll at the bottom of the screen. That opens the tray, with your dice lying on the floor of it and waiting — the throw is yours to make, and the next section is how.

Rolling

The tray opens waiting. Nothing has been thrown, the dice are lying where they fell in, and it stays that way until you ask — the same as the card table, which opens on a bare glass and waits for Draw.

Hold the phone upright and shake it. The dice are thrown, they bounce off the walls and off each other, and they settle. There is no threshold to beat and no gesture to learn: the tray is simulated in the phone's own frame of reference, so tilting pours the dice down the screen and shaking throws them, and both are the same reading arriving from the same sensor.

If your hands are full — or if you have turned motion control off — the Throw button at the top right does exactly the same thing. Close takes you back to the picker.

On a phone that has one, the tray taps back. Each knock you feel is a real wall impact, and its strength is the impulse that die actually delivered — so a D20 arriving hard registers harder than a D4 drifting into a corner.

Reading and holding

A die that has settled on a tray held upright is showing its number to the ceiling and its edge to you. It is genuinely there and genuinely unreadable. So once everything has stopped, Roll Hippo lifts the dice off the floor, turns each one until the face it landed on is square to the glass, and lays them out on a grid.

Nothing is chosen when this happens. The face is read off the orientation the physics arrived at, and only then is the die turned so that you can see what it already said.

• Tap a die to hold it. A held die is pinned: it keeps its number, it is not thrown by the next shake, and the rest of the tray bounces off it as though it were part of the wall. Tap it again to let it go.
• Tap the empty space around the dice to put the whole formation back down on the floor of the tray, and tap again to bring it back up.

Holding is what you want for a game where some dice are kept and the rest re-rolled. Throw, tap the ones you are keeping, shake again — the held ones stay exactly as they are.

Several separate sets

The picker can hold up to four separate sets of dice, and it offers them one at a time rather than all at once: what you are shown is the sets you have started and one empty one after them. So a picker you have just opened has two dots — the set you have and the set you could have — and putting a die in that empty page fills its dot and adds a fresh empty one behind it, up to four.

The dots beneath the rack say which one you are editing — the lit one is the set on screen. Swipe the rack sideways to reach the others. A set you have not started counts for nothing: it is not a box on the tray, and its dot is a hollow ring rather than a filled one.

Take the last die out of a set and you have said you are finished with it, and what happens next depends on where that set sits. If it is the last set in the row, nothing is lost: it goes back to being the empty page the rack always finishes with, and its dot simply goes hollow. If there is a set behind it, the app asks first — because taking that die deletes the set and brings the next one forward. Confirm and the emptied set slides away to the left while the one behind it comes in from the right, keeping its own dice; cancel and nothing at all happens.

Any set can go that way, the first one included. The only set you cannot empty is the last one left: the picker always keeps one set with dice in it, because a picker with none would have nothing to show you and nothing to roll — so on a single set the Remove button greys out at the last die. Empty the first while a second is set up and the second simply becomes the first.

In the tray, the same swipe moves between them — and each set keeps its own result. A set you are not looking at is not simulated at all, which means the numbers it rolled stay the numbers it rolled. Swiping cannot shake them, and neither can anything happening in the set next door.

A set you have not thrown yet is waiting for you: its dice are already lying on the floor, and it rolls when you shake it or press Throw.

The card table

Swipe the picker's panels sideways — or tap the second of the two dots below them — for card mode. It is the picker's other page rather than a corner of it, and an alternative to the dice rather than a substitute for it: every card in the shoe carries one possible outcome of the dice it stands for, so dealing one is the same wager as throwing them.

Card mode's set-up sits in two panels rather than one, because it is about two things. The upper one is the card — which die of it the swatches are painting, and Remove, exactly as the dice page's editor works. The lower one is the shoe: how many decks go into it and where it is cut, neither of which is about any one die. That is why the lower panel stays live on the empty page at the end of the row, where the swatches above it grey out — you can set a new shoe's decks and its cut before you put the first die on its card.

• How many dice a card stands for: one, two or three. Three is the limit because a shoe holds every outcome — two dice is 36 cards, three is 216, and four would be more than a thousand.
• How many decks are shuffled together, up to three.
• Where the shoe is cut: the percentage left when it reshuffles.
• What colour each die is printed in on the card, chosen one die at a time exactly as on the rack.
• Up to four shoes, swiped between exactly as the sets of dice are and arriving the same way: the shoes you have started and one empty one after them, with the dots under the rack saying which one you are on and which of them you have started. Each carries its own dice, its own decks and its own cut — one can be a blackjack shoe and the next a single deck cut to the last card. The empty one on the end has no card at all, which is how you say you only wanted the shoes you have; adding a die to it starts it and offers you another, and taking a shoe's last die away drops it from the row — decks, cut and all — after the same question the sets of dice ask, and with the same slide. A shoe at the end of the row is not asked about and is not deleted; it goes back to being the empty page. Any shoe can go that way and the last one left cannot: there is always one shoe with a card on it.

Dealing opens one table per started shoe, side by side, and a swipe moves between them. They do not touch each other. Each is shuffled separately and dealt separately, and each remembers what has gone out of it, which is the whole point of playing with a shoe rather than a pair of dice — the same reason two sets of dice keep their own rolls on the tray. Closing takes all of them, and the question you are asked before it says so.

On the table itself, Draw turns the next card over. A shake does not, and that is deliberate — see Shake to deal a card under Settings, which is off until you ask for it.

Saved profiles

Beneath the editor is Profiles — the set-ups you have saved, each under a name you chose.

• + New saves what is currently on screen as a new profile and asks what to call it.
• Tap a profile to open it. The title at the top of the screen becomes Roll Hippo — <name>.
• Press and hold a profile for its menu: Save (write what is on screen into that profile), Rename, Share (see below) and Delete.
• Press and hold + New for Reset, which puts the picker back to the set-up the app opens with — two white six-sided dice in one set, nothing in the other two, and the dice page. Your saved profiles are not touched; only the screen is. Its menu has a Share too.

Sharing and scanning

Share is on the menu a profile gives you when you press and hold it, beside Save, Rename and Delete. It turns that profile into a QR code: every die, its kind and its colour, which page you are on, the shoe you built, and the name it is saved under.

A saved profile shares what it holds, not what happens to be on screen — so a profile you have edited without saving still shares the version you kept, and the name on the code always describes the dice inside it. + New has a Share of its own, and that one sends what is on screen at that moment, with no name attached.

Scan is in the menu button at the top left of the picker, alongside Settings and How to use. It opens the camera and reads a code. What happens next depends on the name the code carries:

• A code with no name simply opens, unnamed.
• A code whose name you already have, and which matches what you have saved, opens without a word.
• Anything else asks you first.

No network is involved at any point. The code is the data — it is read off the glass by a camera, and nothing is fetched.

Settings

Settings is the first entry on that same menu — Settings, Scan, and How to use — and it has five controls.

Each one is a line saying what it is doing now, and that line changes with the switch — so what the sheet tells you is true of how it is set rather than true in general. The argument for a setting is not on the sheet at all. It is here, below, which is where somebody who wants one has come looking.

Motion control

On — which is the point of the app — the phone's own movement drives the tray: tilt to pour the dice down the screen, shake to throw them.

Off, the tray is handed a phone that is holding perfectly still. Down is down the screen and stays there, a shake does nothing, and Throw — or Draw, on the cards — is the whole of the interface. It works exactly as it always did.

This is a real setting rather than an accessibility afterthought. A phone flat on a table, a hand that cannot shake one, a game being played on a train — all of them want the dice and none of them wants the accelerometer.

Shake to deal a card

Drawn underneath Motion control, and inside it: it only means anything while that switch is on, and it goes quiet when it is off.

Off, and worth leaving off. A shake on the tray and a shake on the card table look like the same gesture and are not the same act. Shaking dice is the simulation — the box moved, so the dice tumbled — and a throw you did not mean costs you nothing, because you simply throw again.

A shoe has memory, and that is the whole reason to play with one. A card that has been dealt is off the shoe until the cut comes round, so what is left to come has genuinely changed and there is no dealing it back. And a phone handed across a table is a shake — several, usually. That is one player's turn spent on cards nobody drew, and nothing undoes it.

So the gesture is still there, and it is asked for rather than assumed. Turn it on if you play with the phone in your own hand; leave it alone if it goes round the table. Draw turns the next card over either way.

Haptic strength

How hard the phone taps back when a die hits a wall. Dragging the slider plays each notch back at the strength an ordinary throw would produce, so you are comparing sensations rather than reading a number. All the way down is off.

The interface taps too, and at a fixed strength rather than at whatever this slider says: a light tap for a menu entry, a profile you have pressed, or anything you press in the picker — a die picked out of the rack, its colour or its kind, a die added or taken away, the number of decks, the point the shoe is cut at — and a slightly firmer one as a menu opens under your thumb, that one being the only sign a press-and-hold was long enough, since nothing on the screen has moved yet. The cut is the one you drag rather than press, and it counts as the figure changes, so you can land on a number without watching it. Turning the slider all the way down silences all of them as well as the tray.

Timer

Off, and the last control on the sheet. Turn it on and a clock appears between Close and Throw, counting up in minutes and seconds from the last roll — or, on the card table, from the last card.

It measures and does nothing else. Nothing counts down, nothing runs out, and neither screen behaves any differently for it being there: a game with a turn limit keeps the limit where it always was, in the players' heads, and this only saves somebody watching a second phone.

Each set of dice keeps its own clock, for the same reason each keeps its own roll. Swipe to another set and you are told how long ago that one was thrown, not how long ago you last pressed anything — and a set nobody has shaken yet shows a stopped 0:00, which cannot run out however long you leave it. A shake counts as the roll it is, so a tray shaken into a fresh result starts again from zero without anybody touching Throw.

On the cards, a reshuffle stops the clock rather than restarting it: it goes back to 0:00 and stays there, because the glass is bare and there is no card for it to be counting since. The next card starts it again.

Turn limit

Drawn underneath Timer, and inside it, the way Shake to deal is drawn under Motion control: it only means anything while the clock is showing, and it goes quiet when it is not. None to begin with.

Set one — thirty seconds to five minutes, in quarter-minutes — and when a turn runs past it the screen flashes three times, the phone taps three times with it, and the clock turns red and stays red. The next roll, or the next card, puts it back to 0:00 and takes the colour with it.

The flash and the taps are both there because neither one reaches everybody. A phone face up on the table between four players is seen and not felt; a phone in somebody's hand at the far end is felt long before it is looked at. Turning Impact strength all the way down silences the taps, as it silences everything else — the flash stays.

Nothing is prevented and nothing is scored. The clock goes on counting up past the limit rather than down towards it, because how far over a turn has run is the number worth reading and −1:30 is a worse way to say it. Roll Hippo has no opinion about whose turn it is and does not acquire one here: it says the time is up, and what that costs is between the people playing.

The notches are deliberate. A turn limit is a thing people agree on out loud — "about a minute each" — and it is never 47 seconds, so the slider is settable by dragging rather than by aiming.

How the number is decided

Roll Hippo does not pick a result and animate towards it. Each die is thrown with a uniformly random orientation and a randomised speed; from that moment on it is a rigid body in a physics simulation, and where it stops is where it stops. The value you read is read off the die's own orientation once it has settled — the face that finished pointing up, or, for the D4, the face it came to rest on, because a tetrahedron at rest has a vertex pointing at the sky and no face at all.

Three things make that a fair reading rather than a decorative one:

• Every solid is isohedral — each face the same distance from the centre — which is what makes a die fair in the first place.
• Each shape's inertia tensor is computed from its own geometry by decomposing the solid into tetrahedra, not copied from a table. A die whose inertia is wrong is a loaded die.
• Every die is built to the same width across its widest point and given the mass its own volume implies, so a D20 really is heavier than a D4.

The dice are also bevelled, and collision treats them as the polyhedron inflated by that bevel — which is why they roll over an edge onto the next face instead of landing on a corner and stalling. Real dice are made that way for the same reason.

Privacy

Roll Hippo makes no network calls. There is no account, no sign-in, no analytics, no crash reporting, no advertising and no update ping. Your saved profiles and your two settings are stored on the phone, by the phone, and go nowhere else.

The camera is used for exactly one thing — reading a QR code you point it at — and only while the scanner is open. No image is stored or transmitted.

The app works with the SIM removed and in aeroplane mode, because there is nothing for it to reach — the Android release package is built without the INTERNET permission at all.

The full statement is on Roll Hippo's privacy page: what is stored, what each permission is for, and what the app stores themselves see.

If something looks wrong

Shaking does nothing

Check Motion control in Settings. With it off, the tray deliberately ignores the phone and Throw is the only way to roll. The prompt on an unthrown tray tells you which of the two you are in: it reads "Shake to roll" or "Tap Throw to roll".

Shaking deals no card

That is the default. Shake to deal a card in Settings turns it on — and the paragraph beside it is worth reading first, because a dealt card cannot be dealt back. Draw works either way.

I skipped the tour

Open the menu at the top left of the picker and choose How to use. It starts again from the first card, as many times as you like.

A die will not re-roll

It is being held. Tap it once to release it. Held dice survive every throw until you tap them again.

My changes disappeared

Editing the picker does not write to a saved profile. Hold the profile down and choose Save, or use + New to keep the change as a profile of its own.

The screen will not rotate

That is deliberate, and it is not cosmetic. The walls of the tray are fixed to the screen while gravity comes from the accelerometer, so a screen that re-oriented as you tipped the phone would swing the tray out from under the dice while down carried on pointing the same way.