C# binding

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The C# binding is three NuGet packages: RippleFx.Engine, the managed bindings, and one of two engine packages, RippleFx.Engine.Native or RippleFx.Engine.Native.NoPython. Version 1.5.x binds Ripple Effect contract 1.5. MAJOR.MINOR is the engine contract, and the PATCH is the binding’s own. Each binding release pins one engine release, engine-v<version> of the public ripple_engine_releases repository, and the engine packages carry exactly the libraries of that release’s signed archives. Binding 1.5.0 pins engine 1.5.3. The source is at ConnectingTheDots-DCWK/ripple_effect_csharp_integration. The bindings are MIT. The engine binary the native packages carry is under the Ripple Effect Runtime Licence, and its notice must be reproduced wherever your product lists the third-party software it contains.

Everything below is in the RippleFx.Engine namespace. Times are milliseconds throughout.

Packages and installing

Package	What it is	Targets
`RippleFx.Engine`	The managed bindings: `Campaign`, `Session`, `Effect`, `Value`, the records, the exceptions, `Mixer`, `ISpeaker` and `IVoice`, `SoundscapeDriver`, `Player`. No dependencies. Carries no engine.	`netstandard2.1`, `net8.0`; compiled as C# 9
`RippleFx.Engine.Native`	The engine with its Python interpreter, as NuGet ships native code: `runtimes/<rid>/native/`.	every runtime identifier under Platforms
`RippleFx.Engine.Native.NoPython`	The engine without Python: about half the size.	the same

dotnet add package RippleFx.Engine
dotnet add package RippleFx.Engine.Native            # with Python
dotnet add package RippleFx.Engine.Native.NoPython   # or without

Reference exactly one engine package. A project that references both fails to build, with an error naming both. A project that references neither builds, and the first call that needs the engine throws EngineNotFoundException naming the two packages.
The engine packages carry ENGINE-NOTICE.txt and LICENSE-ENGINE.txt at their root. ENGINE-NOTICE.txt is the notice to reproduce.
netstandard2.1 and C# 9 are what Unity compiles and loads.
Ahead of time. Every signature in RippleFx.Engine.Interop is blittable and nothing calls back into managed code, so no marshalling stub is generated at run time. The assembly is marked AOT-compatible for net8.0 (NativeAOT), and the same holds under IL2CPP.
A self-contained or single-file publish takes the engine library with it, as it does any NuGet native asset.
RippleFx.Engine.Interop is the engine’s C ABI as P/Invoke, generated from the engine’s ripple.h with the C names kept: the static class Native and the C structs and enums. Use it, with Campaign.DangerousHandle and Session.DangerousHandle, for a call the bindings do not wrap.

Choosing the variant

The variant is chosen by which engine package you reference. The managed package names neither.

	`RippleFx.Engine.Native`	`RippleFx.Engine.Native.NoPython`
Runs Script nodes and Python snippets	yes	no
A campaign whose `Manifest.Needs` contains `python`	plays	refused at open with `NeedsPythonException`
`RippleEngine.HasPython`, `Session.PythonAvailable`	`true`	`false`
`Session.ConsoleFeed`	runs the line	answers a `PythonFailure` of kind unavailable

The editor’s Needs no Python export is checked by the compiler for exactly the NoPython host.

Platforms

Runtime identifiers	Library	Floor and notes
`win-x64`, `win-arm64`	`ripple_effect_engine.dll`	Built against the dynamic CRT.
`osx-x64`, `osx-arm64`	`libripple_effect_engine.dylib`	macOS 12.0 and up. One library per architecture; a universal app takes both identifiers.
`linux-x64`, `linux-arm64`	shared library	glibc 2.35 and up. Not musl: Alpine has no engine build.
`android-arm64`, `android-x64`	shared library	API 24 and up. .NET for Android packs it under `lib/arm64-v8a/` and `lib/x86_64/`.
`ios-arm64`, `iossimulator-arm64`	`libripple_effect_engine.a`, static	iOS 13.0 and up; a simulator runtime’s own minimum may raise the deployment target. The package’s build targets link the archive into your app and keep and export every C entry point, so the same P/Invokes resolve through the main image. Build one runtime identifier at a time with `-r`, and do not list both in `RuntimeIdentifiers`: a list naming a simulator makes a device build target the simulator.

Not supported: .NET in the browser (browser-wasm). The engine’s web build for native linking needs Emscripten 4.0 or later, and .NET’s wasm-tools workload links with its own older Emscripten (3.1.34 in .NET 8, 3.1.56 in .NET 10), whose optimiser refuses the engine’s objects.

The full matrix of engine builds is Engine targets.

The engine

RippleEngine is a static class describing the library this process loaded.

Member	Type	What it is
`BoundContract`	`const string`	The contract these bindings bind: `"1.5"`.
`Version`	`string`	The loaded library’s version, such as `1.5.3`: the one loaded, not the one built against.
`Contract`	`string`	The contract the loaded library binds.
`HasPython`	`bool`	Whether the loaded library runs scripts: `false` for the `NoPython` one.
`Outstanding`	`long`	How many things the engine handed out and has not had back. Zero whenever no call is in flight.
`EnsureLoaded()`	`void`	Loads the library and checks its contract against `BoundContract`, once. Every handle’s constructor calls it. Throws `EngineNotFoundException`.

Campaign

A Campaign is an opened bundle: immutable, shared by every session made from it, and IDisposable. It may be disposed before its sessions, and they go on working.

Opening

Factory	Opens	Notes
`Campaign.OpenDirectory(string folder)`	The bundle in the folder that holds `campaign.json`.	Files are read as the story asks for them, never from outside the folder.
`Campaign.OpenFiles(IReadOnlyList<BundleFile> files)`	A bundle held in memory: every file of it, by its path inside the bundle.	The bytes are copied. For a packed asset system, a phone’s bundled assets or a console.

BundleFile(string Path, byte[] Bytes) is one file of a bundle in memory. Both factories throw BundleException for a malformed bundle or one from a newer engine, and NeedsPythonException on the NoPython engine for a bundle that needs Python.

Members

Member	Answers	Notes
`Manifest`	`Manifest`	`campaign.json`, read afresh on every call: keep it rather than ask again.
`Board(uint index)`	`Board`	A board, by index into `Manifest.Boards`.
`Soundscape(uint index)`	`Soundscape`	A soundscape, by index into `Manifest.Soundscapes`.
`BoardWithId(string id)`	`uint?`	A board’s index by its id; null when there is no such board.
`Node(uint board, string id)`	`Node?`	A node of a board, for when a trace names one; null when there is none.
`Validate()`	`IReadOnlyList<BundleProblem>`	Everything wrong with the bundle the engine can see without playing it; empty when it is sound.
`MediaPath(uint index)`	`string?`	A medium’s path inside the bundle; null when there is no such medium.
`MediaFile(uint index)`	`string?`	The folder joined with the medium’s path, for a campaign opened from a folder; null otherwise.
`MediaBytes(uint index)`	`byte[]?`	A medium’s bytes; null when there is no such medium.
`Folder`	`string?`	The folder it was opened from; null for a bundle in memory.
`DangerousHandle`	`IntPtr`	The engine’s handle. Good while the campaign is neither disposed nor collected.
`Dispose()`		Releases the handle.

BundleProblem(string Message, string Location) is one finding of Validate().

Manifest

Field	Type	What it is
`Format`	`long`	The bundle format.
`Generator`	`string?`	Who compiled it; null when it does not say.
`TextFormat`	`string`	`markdown` or `html`: what a passage’s text is written in.
`Project`	`Project`	Title, description and languages.
`Entries`	`IReadOnlyList<uint>`	The boards a story may begin on, by index into `Boards`.
`Boards`, `Passages`, `Components`, `Scripts`, `Media`, `Machines`, `Soundscapes`	`IReadOnlyList<Entry>`	The manifest’s tables.
`Cvars`	`IReadOnlyList<Cvar>`	The console variables the campaign declares.
`Needs`	`IReadOnlyList<string>`	What the campaign needs of its host: `python`, when it runs scripts.

Record	Fields
`Project`	`Title`, `Description`, `DefaultLocale` (`string`); `Locales` (`IReadOnlyList<string>`); `Cover` (`string?`, the cover picture’s path inside the bundle)
`Entry`	`Id`, `Name`, `Path` (`string`): one row of a table
`Cvar`	`Name`, `Type` (`string`); `Default` (`Value`)

Boards, nodes and soundscapes

Record	Fields
`Board`	`Id`, `Name` (`string`); `Start` (`long`); `Prime` (`IReadOnlyList<uint>`); `Nodes` (`IReadOnlyList<Node>`)
`Node`	`Id`, `Type`, `Title` (`string`); `Inputs`, `Outputs` (`IReadOnlyList<Port>`); `Data`, `Metadata` (`Value`)
`Port`	`Id` (`string`); `Kind` (`PortKind`: `Control`, `Data`); `Edges` (`IReadOnlyList<Edge>`)
`Edge`	`Node`, `Port` (`long`)
`Soundscape`	`Id`, `Name` (`string`); `Length`, `FadeIn`, `FadeOut` (`long`); `Looping`, `Tied` (`bool`); `Volume` (`double`, default 1.0); `Tracks` (`IReadOnlyList<Track>`)
`Track`	`Media` (`long`, by index into the manifest’s media); `Lane`, `Start`, `ClipStart`, `FadeIn`, `FadeOut`, `Interval` (`long`); `ClipEnd` (`long?`); `Volume`, `Speed` (`double`, default 1.0); `Mode` (`TrackMode`: `Once`, `Looping`, `Auto`)

Session

A Session is one story being played: IDisposable, used by one caller at a time. Every verb answers IReadOnlyList<Effect>, the effects it led to in the order they are applied, with the Turn last.

Creating and resuming

Factory	Notes
`Session.Create(Campaign campaign, SessionConfig config)`	A new session before its first turn. Call `Start()` next.
`Session.Resume(Campaign campaign, string save, ulong seed, SessionOptions? options = null)`	A session picking up a save from `Pause()` or `Checkpoint()` over the same campaign. Call `Start()` next; it answers the turn the save was on. Throws `ResumeException` when the save names a board or node the campaign no longer has.

SessionConfig

Field	Type	Default	What it is
`Board`	`uint`	`0`	The board, by index into the manifest’s boards: usually `Manifest.Entries[0]`.
`EntryNode`	`string?`	`null`	A node to begin at instead of the board’s start.
`Locale`	`string?`	`null`	The language to read in; null for the default. A locale the campaign is not readable in is refused.
`Seed`	`ulong`	`0`	The dice’s seed: the same seed and the same moves play the same story.
`Digest`	`string?`	`null`	The bundle digest a save made from this session is stamped with; null for none.
`Options`	`SessionOptions?`	`null`	Null means `new SessionOptions()`.

SessionOptions

new SessionOptions() reads the engine’s own budgets from the loaded library. Set only what you mean to change.

Field	Type	Default	What it is
`StepBudget`	`uint`	the engine’s	Steps a run may take before it is stopped; 0 stops on the first.
`SilentJumpLimit`	`uint`	the engine’s	Silent jumps between boards before the story is stopped.
`LoopLimit`	`uint`	the engine’s	Times a loop may go round; 0 is no ceiling.
`ScriptDeadlineMs`	`ulong`	the engine’s	How long a script may run before it is stopped. Ignored without Python.
`ScriptMemoryBytes`	`ulong`	the engine’s	How much memory a script may use. Ignored without Python.
`ScriptRecursionDepth`	`uint`	the engine’s	How deep a script may recurse. Ignored without Python.
`Untranslated`	`Untranslated`	`Report`	`Report`: a passage with no text in the locale has empty text and names the locale in `Passage.Untranslated`. `FallBack`: it shows the default locale’s text and still names it.
`Trace`	`bool`	`false`	Whether every verb’s batch carries the run’s trace as `Effect.Trace`.
`TracePayloads`	`bool`	`false`	Whether the trace carries the values that flowed, not only that they did.

Verbs

Verb	Answers	Notes
`Start()`	effects	The first turn, or the turn a resumed save was on.
`Choose(int index)`	effects	Takes the choice at `index` among those the passage offers. A negative index throws `ArgumentOutOfRangeException`.
`Leave()`	effects	The reader leaves the passage without choosing.
`Answer(IEnumerable<KeyValuePair<string, Value>>? fields)`	effects	Answers the form showing, field by field in the order given. `null` is the reader leaving the form.
`Elapsed()`	effects	Answers a `Hold` once your clock says it is over.
`SetLocale(string locale)`	effects	Changes the language; the turn the story is on is answered again in it.
`Restart()`	effects	Starts the story over from its first turn.
`Stop()`	effects	Stops the story for good.
`Pause()`	`Paused`	Puts the story down: its save and what pausing did. Pausing stops the story; resuming is a new session from the save.
`Checkpoint()`	`string?`	A save of the turn the story is on, without stopping it; null when there is nothing to save.
`ConsoleFeed(string code)`	`ConsoleResult`	Runs a line of Python in the story’s interpreter, as the editor’s console does.
`WriteCvar(string name, Value value)`	`CvarChange`	Writes a console variable.
`ResetCvar(string name)`	`CvarChange`	Puts a console variable back to its default.
`ResetAllCvars()`	effects	Puts every console variable back to its default.
`RemoveEntity(string key)`	`EntityRemoval`	Removes an entity from the story.

Result record	Fields
`Paused`	`Save` (`string?`, JSON; null when there was nothing to save); `Effects`
`CvarChange`	`Outcome` (`CvarWrite`: `Done`, `Unknown`, `Refused`); `Refusal` (`string?`, the sentence when refused); `Effects`
`EntityRemoval`	`Removed` (`bool`); `Effects`
`ConsoleResult`	`Result` (`PythonResult`); `Effects`
`PythonResult`	`Value` (`Value`); `Output` (`string`); `Error` (`PythonFailure?`)
`PythonFailure`	`Kind` (`uint`: 0 Python, 1 timeout, 2 refused, 3 closed, 4 host error, 5 unavailable); `Exception` (`string?`, the exception’s type for kind 0); `Message` (`string`); `Line` (`uint?`); `Traceback` (`string?`)

Every Effects field is an IReadOnlyList<Effect> to dispatch like any verb’s answer.

Readers

Member	Type	What it is
`Board`	`uint`	The board the story is on, by index into the manifest’s boards.
`Locale`	`string`	The language the story reads in.
`DefaultLocale`	`string`	The campaign’s default language.
`Ambience`	`Ambience?`	The soundscape in force; null for silence.
`Entities`	`IReadOnlyList<Entity>`	What the story has made.
`Memory`	`Memory`	The story’s own store.
`Cvars`	`IReadOnlyList<CvarSnapshot>`	Every console variable and its value.
`Guard`	`GuardReport`	What the script guard has had to do so far: `Abandoned` (`IReadOnlyList<string>`, the nodes whose scripts were abandoned), `Refused` (`uint`), `Exhausted` (`bool`).
`PythonAvailable`	`bool`	Whether this session can run scripts: `false` on the `NoPython` engine.
`DescribeCvarWrite(string name, Value value)`	`string?`	Why the write would be refused; null when it would not. Writes nothing.
`SetTrace(bool enabled)`	`void`	Turns `Effect.Trace` on or off.
`SetTracePayloads(bool enabled)`	`void`	Turns traced payloads on or off.
`DangerousHandle`	`IntPtr`	The engine’s handle, for a call the bindings do not wrap.

Saving and the generator

A save is JSON text. Keep it with the seed and the locale.
A save carries no generator state and no soundscape position: the same seed gives the same future rolls, and a soundscape starts from the top on resume.
Generator (get and set) is the dice’s state, Generator(uint Lo, uint Hi). Read it before saving and set it on the resumed session for the dice to run on exactly.

Effects

Effect is an abstract record with a closed set of nested sealed records, so Effect.Trace never collides with System.Diagnostics.Trace. Every effect is a copy: nothing in it points into the engine, and it outlives the session and the campaign.

Member	What it is
`IsTurn`	`true` for a Turn: where the story now is. Exactly one closes every batch that moved the story.
`IsOver`	`true` for `Ended`, `Failed` and `Stopped`.

Turns

Effect	Fields	Answered with
`Effect.Show`	`Passage` (`Passage`)	`Choose` or `Leave`
`Effect.Ask`	`Prompt` (`Prompt`)	`Answer`
`Effect.Hold`	`Ms` (`ulong`)	`Elapsed`, once your clock says `Ms` have passed
`Effect.Ended`	`Title` (`string?`); `RanOut` (`bool`, true when the story ran out of road rather than reaching an End)	nothing; `IsOver`
`Effect.Failed`	`Message` (`string`); `Node` (`string?`)	nothing; `IsOver`
`Effect.Stopped`	none	nothing; `IsOver`

Along the way

Effect	Fields	What it is
`Effect.Jumped`	`Board` (`uint`); `Node` (`string?`)	The story moved to another board, by index into the manifest’s boards.
`Effect.AmbienceChanged`	`Ambience` (`Ambience?`)	The soundscape now in force; null for silence. A fact for a HUD or a save screen, not a command for the speaker.
`Effect.Audio`	`Command` (`AudioCommand`)	A command for the sound: give it to `SoundscapeDriver.Apply`.
`Effect.Changed`	`Entities` (`IReadOnlyList<Entity>?`); `Memory` (`Memory?`); `Cvars` (`IReadOnlyList<CvarSnapshot>?`)	Which stores moved; a store that did not is null. The first `Changed` after `Start` names all three.
`Effect.Callback`	`Event` (`CallbackEvent`)	A named callback the author declared, fired.
`Effect.Trace`	`Event` (`RunEvent`)	One event of the run’s trace, when the session traces.

Records

Record	Fields
`Passage`	`Node`, `Title` (`string`); `Text` (`string`, Markdown, or HTML when `Manifest.TextFormat` says so); `Choices` (`IReadOnlyList<Choice>`); `Sources` (`IReadOnlyList<LocaleText>?`, the text in every language when the compiler kept them); `Snippets` (`IReadOnlyList<Snippet>`); `Media` (`IReadOnlyList<MediaLink>`); `Untranslated` (`string?`, the language the text is missing in); `Soundscape` (`Soundscape?`, the one the passage names); `Silence` (`bool`, true when the passage asks for silence)
`Choice`	`Port` (`string`, the control output the flow leaves by); `Text` (`string`); `Available` (`bool`, false for a choice not open now; still shown, and choosing it throws `HostException` with `Code.ChoiceSpent`)
`LocaleText`	`Locale`, `Text` (`string`)
`Snippet`	`Code` (`string`); `IsInline` (`bool`)
`MediaLink`	`Link` (`string`, the name the author linked it under); `Media` (`uint`, by index into the manifest’s media)
`Prompt`	`Node`, `Title` (`string`); `Fields` (`IReadOnlyList<PromptField>`)
`PromptField`	`Name`, `Type` (`string`: `number`, `bool`, `string`, `numberList`, `boolList`, `stringList` or `json`); `Default` (`Value`). Answer with the matching type.
`Ambience`	`Soundscape` (`Soundscape`); `Board` (`uint`); `Node` (`string`, the node that set it)
`Entity`	`Key`, `Label` (`string`); `Component` (`string?`); `Values` (`Value`, a map, field by field)
`Memory`	`Nodes` (`Value`, a map, node by node); `Machines` (`IReadOnlyList<KeyValuePair<string, string>>`, each state machine and the state it is in)
`CvarSnapshot`	`Name`, `Type` (`string`); `Default`, `Value` (`Value`)
`CallbackEvent`	`Callback` (`string`, the name a handler is registered by); `Event` (`uint`, a `RippleCallbackKind`); `EventName` (`string`, such as `cvar.changed`); `Board` (`uint?`); `Node`, `Name` (`string?`); `From`, `To` (`Value?`); `Index` (`uint?`). Which optional fields are set depends on the event.
`AudioCommand`	`Kind` (`AudioKind`: `Play`, `Stop`, `Cut`, `Cue`); `Soundscape` (`Soundscape?`, Play: what to play); `FadeMs` (`ulong`, Play: the fade-in, Stop: the fade-out); `Media` (`uint`, Cue: the medium); `Volume`, `Speed` (`double`, default 1.0); `Node` (`string?`, Cue: the node that asked for it)
`RunEvent`	`Kind` (`RunEventKind`: `RunStarted`, `NodeStarted`, `NodeFinished`, `MemoHit`, `Diagnostic`, `Log`, `RunFinished`); `Run`, `Board`, `Sequence`, `Step`, `Steps` (`uint`); `Node`, `Entry`, `Message` (`string`); `Primed`, `Flowed` (`IReadOnlyList<string>`); `EnteredVia`, `Error`, `FailedNode` (`string?`); `Pulled`, `Cancelled` (`bool`); `Inputs`, `Outputs` (`IReadOnlyList<TraceValue>`); `Outcome` (`uint`: 0 done, 1 failed); `Diagnostic` (`RunDiagnostic?`); `Level` (`uint`: 0 debug, 1 info, 2 warning, 3 error); `Data` (`Value?`). Read the fields by `Kind`.
`TraceValue`	`FromNode`, `FromPort` (`string`); `ToNode`, `ToPort` (`string?`); `Payload` (`PayloadKind`: `Present`, `Withheld`, `Absent`); `Value` (`Value`, set when `Payload` is `Present`)
`RunDiagnostic`	`Issue` (`uint`: 0 ambiguous flow, 1 multiple inputs, 2 producer not run, 3 re-entered); `Message` (`string`); `Node`, `Port` (`string?`); `Wires` (`uint?`)

The uint kinds match the enums of the same name in RippleFx.Engine.Interop, such as RippleCallbackKind and RippleRunIssue.

Values

Value is a sealed, immutable class: a story’s value. ValueKind is Null, Bool, Int, Float, Text, List or Map.

C#	Story value	Make one	Read it
none	null	`Value.Null`	`IsNull`
`bool`	Bool	`Value.Bool(b)`, or implicit from `bool`	`AsBool()`
`long`	Int	`Value.Int(n)`, or implicit from `int` or `long`	`AsInt()`
`double`	Float	`Value.Float(x)`, or implicit from `double`	`AsFloat()`
`string`	Text	`Value.Text(s)`, or implicit from `string` (`null` becomes `Value.Null`)	`AsText()`
`IReadOnlyList<Value>`	List	`Value.List(IEnumerable<Value>)`, `Value.List(params Value[])`	`AsList()`
`IReadOnlyList<KeyValuePair<string, Value>>`	Map	`Value.Map(IEnumerable<KeyValuePair<string, Value>>)`, `Value.Map(params (string Key, Value Value)[])`	`AsMap()`, `Find(key)`

An Int and a Float never become each other. 7 and 7.0 are different values, and ToString() prints them differently.
A map keeps the order it was written in, and its equality includes that order. A map key is never null.
A null item or map value becomes Value.Null.
AsBool(), AsInt() and the rest throw InvalidOperationException for a value of another kind.
Find(string key) answers a map’s value under the key, or null for a missing key or for a value that is not a map.
Equals and == compare what is held; a value implements IEquatable<Value>.
ToString() is JSON-like text for a log or a debugger. ToStoryText() asks the engine for the text a passage would print.

Player

Player is the loop over a session, written once: IDisposable, owning no clock and no thread.

public Player(Session session, PlayerHandlers handlers, Func<ulong>? now = null)

The player owns session from then on and disposes it. now is the clock in milliseconds; Clocks.Steady() when null.

PlayerHandlers

Field	Type	What it is
`OnEffect`	`Action<Effect>?`	Every effect, in the order the engine produced it.
`OnError`	`Action<Exception>?`	The failure of a verb the player made by itself (the `Elapsed` after a hold), or an exception from a handler. Delivery goes on either way. Without one, a self-made verb’s failure is thrown from `Update()` and a handler’s is lost.
`Audio`	`SoundscapeDriver?`	Where the story’s sound goes: the player applies every `Effect.Audio` to it. Without one, nothing is heard.

Members

Member	What it does
`Start()`, `Choose(int)`, `Leave()`, `Answer(fields)`, `SetLocale(string)`, `Restart()`, `Stop()`	The session’s verbs. The player delivers the batch they answer instead of returning it. After `Dispose` they do nothing.
`Pause()`	Puts the story down and answers its save, `string?`. Null, and nothing stopped, unless the story is on a passage or a prompt.
`Update()`	Call it from your loop. Answers a hold whose time has come with `Elapsed()`.
`Turn`	`Effect?`: the last Turn delivered; null before `Start()`.
`HoldDue`	`ulong?`: when the pending hold is due by the player’s clock; null when none is.
`Session`	The session underneath, for what the player does not wrap. A verb called on it goes round the player and its batch is not delivered.
`OnCallback`, `RemoveCallback`, `OnAnyCallback`, `ClearCallbacks`, `CallbackMisses`	The callback table: Named callbacks.
`Dispose()`	Delivers nothing more, moves the story no further, and disposes the session.

Delivering a batch

For each effect in order, the player:

records it as Turn when it is a Turn;
applies an Effect.Audio to Audio;
dispatches an Effect.Callback through the callback table;
calls OnEffect.

When the batch ends with Effect.Hold, HoldDue is set to the clock plus Ms, and the next Update() at or after it calls Elapsed(). Any verb clears a pending hold.

A verb called from inside a handler throws ReentrantVerbException (Code.Reentrant): the rest of the batch would arrive after the new one. Queue the verb and call it after the handler returns.

Named callbacks

The author declares a callback’s name and event; you register a handler against the name on the Player. The engine never sees the table.

Member	What it does
`OnCallback(string name, Action<CallbackEvent> handler)`	Calls `handler` whenever the callback named `name` fires, replacing any handler already under that name. Names are compared ordinally.
`RemoveCallback(string name)`	Removes the handler under `name`.
`OnAnyCallback(Action<CallbackEvent> handler)`	Calls `handler` for every callback that fires, registered or not. Adds to any already there.
`ClearCallbacks()`	Removes every named and every catch-all handler.
`CallbackMisses`	`long`: how many callbacks fired with nothing registered under their name.

A handler is read-only. It cannot change what the story does; the story plays on identically with nobody listening.
A miss is ordinary, not a failure: it is counted in CallbackMisses and delivery goes on.
A handler that throws is absorbed: the exception goes to OnError, and the rest of the batch is still delivered.
A handler runs inside the verb, on the thread that called it, and cannot call a verb (see Player).
A name is the only join between the author’s declaration and your code. A rename on the author’s side breaks the match without any diagnostic.

A host not using Player reads Effect.Callback from the batch and looks up Event.Callback in a table of its own.

Sound

No speaker ships. The session says what the story asks for as Effect.Audio; the engine’s scheduler (Mixer) decides every voice; SoundscapeDriver drives the scheduler; your ISpeaker makes the sound. The contract is docs/speaker.md.

AudioCommand

`Kind`	Fields used	What it asks
`Play`	`Soundscape`, `FadeMs` (fade-in)	Play a soundscape.
`Stop`	`FadeMs` (fade-out)	Stop the soundscape.
`Cut`	none	Stop everything at once, cues included.
`Cue`	`Media`, `Volume`, `Speed`, `Node`	Play a sound once.

SoundscapeDriver

public SoundscapeDriver(Campaign campaign, ISpeaker speaker, SoundscapeOptions? options = null)

`SoundscapeOptions` field	Type	Default	What it is
`MaxCues`	`uint`	`8`	How many cues may sound at once; the oldest gives way.
`GainStep`	`double`	`0.004`	The smallest change of gain worth a gain command.
`Muted`	`bool`	`false`	Start muted.
`Now`	`Func<ulong>?`	`null`	The clock in milliseconds; `Clocks.Steady()` when null.

Member	What it does
`Apply(AudioCommand command)`	Obeys one of the session’s audio commands. A `Play` with no soundscape, and a `Cue` whose medium has no path, are ignored.
`Update()`	Call it from your loop: hears what the voices reported and moves the timeline on. The editor ticks every 25 ms, and more often loses nothing.
`Pause()`, `Resume()`	Holds every voice and the timeline with them, and lets them go. Does not pause the story.
`Muted`	`bool`, get and set: mutes or unmutes at once. The scheduler writes every gain as zero and remembers the rest.
`Playing`	`string?`: the soundscape in force, by id, sounding or waiting its turn.
`Idle`	`bool`: whether nothing sounds, waits or cues.
`Voices`	`int`: how many voices the speaker holds open now.
`Dispose()`	Stops every voice the speaker holds, and the scheduler with them.

The driver does what the scheduler asks of a host, so a speaker must not: the tick, a late voice (the time Open took, times Rate, is added to FromMs, and a looping clip wraps inside its loop; a clip already over is reported ended), reporting voices ended or measured, telling the scheduler about tracks with no file, mute, and the handover between soundscapes. A failure inside the scheduler stops the sound rather than the story: the driver swallows it. The driver reads media paths from its campaign, so keep the campaign undisposed while the driver is in use.

ISpeaker and IVoice

public interface ISpeaker
{
    IVoice? Open(VoiceSource source, VoiceRole role, VoiceEvents events);
    bool Resolves(VoiceSource source);
}

public interface IVoice
{
    void Play(VoicePlay request);
    void SetGain(double gain);
    void Pause();
    void Resume();
    void Stop();
}

They are interfaces, so a MonoBehaviour or a Godot Node can be the speaker.

Member	Obligation
`ISpeaker.Open`	Return once the voice can begin at once: the file opened, or enough of it decoded. Return null when the file cannot be played; that is heard as silence and never retried. Keep `events` with the voice. `role` is a hint: a `Track` may be minutes long and is usually better streamed, a `Cue` is short and must start on time. For a campaign opened from memory `source.File` is null: read `Campaign.MediaBytes(source.Media)`.
`ISpeaker.Resolves`	Asked before a soundscape plays. Answer false for a medium the speaker cannot play, so the track is told to the scheduler as silence up front. Answer true when unsure. Required; there is no default.
`IVoice.Play`	Begin at once, replacing whatever the voice was playing. May be called again on the same voice for a gapless bed whose file ended. Play from `FromMs` to `ToMs`, or to the file’s end. When `Looping`, reaching `ToMs` comes round to `LoopFromMs`, not `FromMs`.
`IVoice.SetGain`	Write a new gain. The scheduler writes one every tick a fade moves, so smooth between them over a few milliseconds.
`IVoice.Pause`, `IVoice.Resume`	Hold the voice exactly where it is, and let it go again.
`IVoice.Stop`	End the voice for good and release its resources. No `Ended` follows.
`VoiceEvents.Ended()`	Call once per play, when a non-looping voice reaches the end of what it was given. Never after `Stop()`, never for a looping voice.
`VoiceEvents.Duration(double ms)`	Call once, when the file’s length is known.

Both VoiceEvents calls are thread-safe and may come from an audio thread; the driver hears them on its next Update(). A call from a voice that was stopped, or after the driver is gone, is ignored.

The gain scale is cubic. A speaker writing amplitude writes gain * gain * gain.

Record or enum	Fields
`VoiceSource`	`Media` (`uint`, by index into the manifest’s media); `Path` (`string`, inside the bundle); `File` (`string?`, on disk, for a campaign opened from a folder)
`VoicePlay`	`FromMs` (`double`); `ToMs` (`double?`, the file’s end when null); `Gain` (`double`, 0 to 1 on the cubic scale); `Rate` (`double`, 1 is as recorded); `Looping` (`bool`); `LoopFromMs` (`double`)
`VoiceRole`	`Track`, `Cue`
`Clocks.Steady()`	`Func<ulong>`: milliseconds since the clock was made, monotonic, from `Stopwatch`

Mixer

Mixer is the engine’s scheduler, raw, for a host not using the driver: commands in, IReadOnlyList<VoiceCommand> out, your clock on every verb. A host that uses it directly owes the driver’s duties above by hand.

Member	What it does
`Mixer.Create(uint maxCues = 8, double gainStep = 0.004)`	A new scheduler.
`Play(ulong nowMs, Soundscape scape, IReadOnlyList<uint>? unresolved = null, ulong atMs = 0, bool muted = false)`	Plays a soundscape from `atMs` into it. Tracks listed in `unresolved`, by index, are heard as silence.
`Stop(nowMs)`, `Cut(nowMs)`, `Pause(nowMs)`, `Resume(nowMs)`, `Tick(nowMs)`	The scheduler’s verbs.
`Cue(ulong nowMs, uint media, double volume, double speed)`	Plays a sound once.
`VoiceEnded(ulong nowMs, ulong voice)`	A voice reached its end.
`DurationKnown(ulong voice, ulong ms)`	A voice’s file length is known.
`Muted`	`bool`, get and set.
`PlayingId`, `FinishingId`	`string?`: the soundscape in force, and the one fading out, by id.
`State`	`Phase?`; `TrackState(uint track)` answers `Phase`. `Phase` is `Queued`, `Starting`, `Playing`, `Finishing`, `Finished`.
`PositionMs` (`ulong`), `Pass` (`uint`), `RanOut`, `IsPaused`, `IsIdle` (`bool`)	Where the scheduler is. `IsIdle` is when a tick may rest.
`Dispose()`	Releases the scheduler.

VoiceCommand fields: Kind (VoiceKind: Open, Gain, Stop, Pause, Resume); Voice (ulong); Media, Track (uint); FromMs, LoopFromMs (ulong); ToMs (ulong?); Gain (double); Rate (double, default 1.0); Looping (bool); Role (VoiceRole).

Errors

Every failure the engine reports is a RippleException subclass. Failure carries what the engine said, and Code is Failure.Code. A verb refused with a HostException moved nothing.

Exception	`Code` values	Meaning	Met in
`BundleException`	`BundleFormat` (1), `BundleVersion` (2)	A document of the bundle is malformed or missing, or is from a version this engine cannot read.	Normal use: opening a bad or newer bundle.
`NeedsPythonException`	`NeedsPython` (3)	The bundle needs Python, and this is the `NoPython` engine.	Normal use: opening.
`HostException`	`WrongTurn` (10), `NoSuchChoice` (11), `ChoiceSpent` (12), `Stopped` (13), `NothingAsked` (14), `UnknownLocale` (15)	A verb that does not answer the turn, a choice past those offered, a choice used up or closed, a session that has stopped, a verb before `Start()`, a language the campaign is not readable in.	A host bug, except `ChoiceSpent` when you offer an unavailable choice and `UnknownLocale` from user input.
`ResumeException`	`BoardGone` (20), `NodeGone` (21)	A save names a board or node the campaign no longer has.	Normal use: a save from an older build of the story.
`InvalidArgumentException`	`InvalidArgument` (-1)	A malformed argument: a null handle, text that is not UTF-8, a value out of range. Also any code the binding does not know.	A bug.
`EngineTrapException`	`Trap` (-2)	The engine panicked, now or earlier on this handle.	A bug in the engine.
`ReentrantVerbException`	`Reentrant` (-100)	A `Player` verb called while it was delivering a batch. The binding’s own code.	A host bug.
`EngineNotFoundException`	none; derives from `Exception`	The engine library could not be loaded for this platform, or binds another contract.	Packaging: reference exactly one engine package of the same `MAJOR.MINOR`.

Code.Success (0) is never thrown.

`Failure` field	Type	Set for
`Code`, `Message`	`Code`, `string`	every failure
`Location`	`string?`	`BundleFormat`: the document at fault
`Found`, `Supported`	`long`	`BundleVersion`: the bundle’s format, and the newest this engine reads
`Oldest`	`long?`	`BundleVersion`: the oldest, when there is a floor
`Asked`, `Answered`	`uint`	`WrongTurn`: what the story was asking (`RippleTurnKind`: 0 present, 1 ask, 2 wait, 3 ended, 4 failed, 5 stopped) and the verb that answered (`RippleVerb`: 0 choose, 1 answer, 2 elapsed)
`Offered`, `Chosen`	`uint`	`NoSuchChoice`: how many choices were offered, and the index taken
`Subject`	`string`	the choice, locale, board or node a host or resume error is about
`Node`	`string`	`NodeGone`: the node

Other exceptions the bindings throw:

ObjectDisposedException from any member of a disposed Campaign, Session or Mixer.
ArgumentOutOfRangeException from Choose with a negative index; leave with Leave().
InvalidOperationException from Value.AsBool() and the other readers for a value of another kind.

A trap poisons the handle. After EngineTrapException, dispose the session (and the campaign, if the trap came from it), open again, and resume from the last checkpoint. Every later call on a poisoned handle throws EngineTrapException again.

Threading and lifetime

One caller at a time per handle. A Campaign, Session or Mixer is not thread-safe. A handle may move between threads.
The engine starts no thread, never sleeps and never reads a clock. A Hold is answered by your clock. Player and SoundscapeDriver read the clock they were given and own no thread: your game loop is the timer.
VoiceEvents is the one thing callable from any thread.
Every verb is synchronous. A script runs inside the verb that reached it, for up to ScriptDeadlineMs. If that cannot be spent on your main thread, own the session on a worker and marshal the effects back: they are values.
Everything a verb answers is a copy. Effects, passages and values are C# records that outlive the session and the campaign. The engine’s batch is freed before the verb returns, and RippleEngine.Outstanding is zero whenever no call is in flight.
Campaign, Session, Mixer, SoundscapeDriver and Player are IDisposable. A forgotten Dispose is collected by the finalizer rather than leaked. A disposed handle throws ObjectDisposedException rather than reaching the engine.
A session outlives its campaign: dispose the campaign first and the session goes on working.
Player owns its session and disposes it. It does not own its SoundscapeDriver.

A complete host

A terminal host over a bundle folder: two sittings with a save between them, a speaker that prints what it would play, the author’s callbacks, and recovery from a trap.

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Threading;
using RippleFx.Engine;

public static class Host
{
    static readonly ulong Seed = (ulong)DateTime.UtcNow.Ticks;
    static readonly SessionOptions Options = new SessionOptions { Untranslated = Untranslated.FallBack };
    static readonly Queue<Action> Later = new Queue<Action>();   // verbs a handler asked for
    static string? autosave;                                      // the last Checkpoint(), kept with Seed

    public static int Main(string[] args)
    {
        var folder = args[0];
        try
        {
            Console.WriteLine($"engine {RippleEngine.Version}, contract {RippleEngine.Contract}, Python {RippleEngine.HasPython}");

            using var campaign = Campaign.OpenDirectory(folder);
            var manifest = campaign.Manifest;                     // read once and kept
            foreach (var problem in campaign.Validate())
                Console.Error.WriteLine($"{problem.Location}: {problem.Message}");

            var config = new SessionConfig
            {
                Board = manifest.Entries[0],
                Locale = manifest.Project.DefaultLocale,
                Seed = Seed,
                Options = Options,
            };

            using var audio = new SoundscapeDriver(campaign, new LoggingSpeaker(campaign));

            // The first sitting: three passages, then the story is put down.
            string? save;
            using (var player = NewPlayer(Session.Create(campaign, config), audio))
            {
                player.Start();
                save = Play(player, audio, passages: 3) ? player.Pause() : null;
            }

            // The second sitting: a new session from the save, with the same seed.
            if (save != null)
            {
                using var player = NewPlayer(Session.Resume(campaign, save, Seed, Options), audio);
                player.Start();                                   // re-shows the turn the save was on
                Play(player, audio, passages: int.MaxValue);
            }
            return 0;
        }
        catch (EngineNotFoundException error)
        {
            Console.Error.WriteLine(error.Message);               // names the packages to reference
            return 3;
        }
        catch (NeedsPythonException)
        {
            Console.Error.WriteLine("This campaign runs Python: reference RippleFx.Engine.Native.");
            return 2;
        }
        catch (BundleException error)
        {
            Console.Error.WriteLine($"{error.Failure.Location}: {error.Message}");
            return 2;
        }
        catch (ResumeException)
        {
            Console.Error.WriteLine("This save is from an older build of the story.");
            return 2;
        }
        catch (EngineTrapException) when (autosave != null)
        {
            // The handles that saw the trap are poisoned: open again and resume from the checkpoint.
            using var campaign = Campaign.OpenDirectory(folder);
            using var audio = new SoundscapeDriver(campaign, new LoggingSpeaker(campaign));
            using var player = NewPlayer(Session.Resume(campaign, autosave!, Seed, Options), audio);
            player.Start();
            Play(player, audio, passages: int.MaxValue);
            return 0;
        }
    }

    static Player NewPlayer(Session session, SoundscapeDriver audio)
    {
        var player = new Player(session, new PlayerHandlers
        {
            Audio = audio,                                        // every Effect.Audio goes to the driver
            OnError = error => Console.Error.WriteLine($"host: {error.Message}"),
            OnEffect = effect =>
            {
                if (effect is Effect.Changed { Cvars: { } cvars })
                    foreach (var cvar in cvars)
                        Console.WriteLine($"  [{cvar.Name} = {cvar.Value}]");
            },
        });

        player.OnCallback("chapterTwoBegan", fired => Console.WriteLine($"  [chapter two, board {fired.Board}]"));
        // A verb inside a handler throws ReentrantVerbException: queue it for after delivery.
        player.OnCallback("quitToTitle", fired => Later.Enqueue(() => player.Stop()));
        player.OnAnyCallback(fired => Console.WriteLine($"  [{fired.Callback}: {fired.EventName}]"));
        return player;
    }

    // Plays until the story is over (false) or `passages` passages have been answered (true).
    static bool Play(Player player, SoundscapeDriver audio, int passages)
    {
        var answered = 0;
        while (true)
        {
            audio.Update();                                       // the sound's tick
            player.Update();                                      // answers a Hold that has come due
            while (Later.Count > 0) Later.Dequeue()();

            switch (player.Turn)
            {
                case null:
                case Effect { IsOver: true }:
                    Report(player.Turn);
                    return false;
                case Effect.Hold:
                    Thread.Sleep(25);                             // a frame; the engine never sleeps
                    break;
                case Effect.Show shown:
                    if (answered++ == passages) return true;
                    autosave = player.Session.Checkpoint() ?? autosave;
                    Choose(player, shown.Passage);
                    break;
                case Effect.Ask asked:
                    player.Answer(Fill(asked.Prompt));            // null leaves the form
                    break;
            }
        }
    }

    static void Choose(Player player, Passage passage)
    {
        Console.WriteLine($"\n== {passage.Title} ==\n{passage.Text}");   // Markdown or HTML, by Manifest.TextFormat
        if (passage.Untranslated != null)
            Console.WriteLine($"(not translated into {passage.Untranslated})");
        if (passage.Choices.Count == 0)
        {
            player.Leave();                                       // a dead end: leaving is the only answer
            return;
        }
        for (var i = 0; i < passage.Choices.Count; i++)
        {
            var choice = passage.Choices[i];
            Console.WriteLine($"  {i + 1}. {choice.Text}{(choice.Available ? "" : " (unavailable)")}");
        }
        while (true)
        {
            Console.Write("> ");
            var line = Console.ReadLine();
            if (line == null)
            {
                player.Leave();                                   // the reader leaves the passage
                return;
            }
            if (!int.TryParse(line, NumberStyles.Integer, CultureInfo.InvariantCulture, out var picked)
                || picked < 1 || picked > passage.Choices.Count)
                continue;
            try
            {
                player.Choose(picked - 1);
                return;
            }
            catch (HostException error) when (error.Code == Code.ChoiceSpent)
            {
                Console.WriteLine("That way is closed.");          // nothing moved: ask again
            }
        }
    }

    static IEnumerable<KeyValuePair<string, Value>>? Fill(Prompt prompt)
    {
        Console.WriteLine($"\n-- {prompt.Title} --");
        var answers = new List<KeyValuePair<string, Value>>();
        foreach (var field in prompt.Fields)
        {
            Console.Write($"{field.Name} [{field.Default}]: ");
            var line = Console.ReadLine();
            if (line == null) return null;                        // the reader leaves the form
            var value = line.Length == 0 ? field.Default : field.Type switch
            {
                "number" => long.TryParse(line, NumberStyles.Integer, CultureInfo.InvariantCulture, out var whole)
                    ? Value.Int(whole)
                    : Value.Float(double.Parse(line, CultureInfo.InvariantCulture)),
                "bool" => Value.Bool(line == "y"),
                _ => Value.Text(line),                            // the list types and json need parsing of their own
            };
            answers.Add(new KeyValuePair<string, Value>(field.Name, value));
        }
        return answers;
    }

    static void Report(Effect? turn)
    {
        switch (turn)
        {
            case Effect.Ended ended:
                Console.WriteLine(ended.RanOut ? "\n(the story ran out)" : $"\n{ended.Title ?? "The end"}");
                break;
            case Effect.Failed failed:
                Console.WriteLine($"\nThe story could not go on at {failed.Node}: {failed.Message}");
                break;
            case Effect.Stopped:
                Console.WriteLine("\n(stopped)");
                break;
        }
    }
}

// Prints what it would play. A real speaker opens the file in your audio API.
sealed class LoggingSpeaker : ISpeaker
{
    private readonly Campaign campaign;

    public LoggingSpeaker(Campaign campaign) => this.campaign = campaign;

    public bool Resolves(VoiceSource source) => true;            // true when unsure

    public IVoice? Open(VoiceSource source, VoiceRole role, VoiceEvents events)
    {
        // A campaign opened from memory has no File: the bytes come from the campaign.
        var bytes = source.File == null ? campaign.MediaBytes(source.Media) : null;
        if (source.File == null && bytes == null) return null;   // silence, never retried
        return new LoggingVoice(source.Path, role);              // a real voice keeps `events`
    }
}

sealed class LoggingVoice : IVoice
{
    private readonly string path;
    private readonly VoiceRole role;

    public LoggingVoice(string path, VoiceRole role)
    {
        this.path = path;
        this.role = role;
    }

    public void Play(VoicePlay request) =>
        Console.WriteLine($"  [{role} {path}] from {request.FromMs:F0} ms, amplitude {Math.Pow(request.Gain, 3):F2}"
            + (request.Looping ? $", looping back to {request.LoopFromMs:F0} ms" : ""));

    public void SetGain(double gain) { }                          // amplitude is gain³, smoothed over a few ms
    public void Pause() { }
    public void Resume() { }
    public void Stop() => Console.WriteLine($"  [{role} {path}] stop");   // for good: no Ended after this

    // A real voice calls events.Ended() from its audio thread at the end of a non-looping play,
    // and events.Duration(ms) once the file's length is known.
}

The repository’s examples/ConsolePlayer is a runnable terminal player over any bundle folder.

Embedding the engine: what a host is responsible for, and what the engine does itself.
How the engine ships: engine releases, contracts and the two variants.
Play a campaign in your program: the steps from an exported bundle to a running story.
Host callbacks: why the author declares a callback and the host registers it.
Export a project or campaign: making the bundle this binding opens.

C# binding

Packages and installing

Choosing the variant

Platforms

The engine

Campaign

Opening

Members

Manifest

Boards, nodes and soundscapes

Session

Creating and resuming

SessionConfig

SessionOptions

Verbs

Readers

Saving and the generator

Effects

Turns

Along the way

Records

Values

Player

PlayerHandlers

Members

Delivering a batch

Named callbacks

Sound

AudioCommand

SoundscapeDriver

ISpeaker and IVoice

Mixer

Errors

Threading and lifetime

A complete host

Related