Dialogue systems

Model conversations as a graph: nodes hold lines, choices branch the flow, conditions gate options, and variables remember what the player did. The first real decision is build vs. buy — adopt a proven authoring tool (Ink or Yarn Spinner) or write a small data-driven runner. This skill owns both Ink and Yarn; the visual-novel and rpg genres consume it.

When to use

• Use to design branching conversations, choice menus, or narrative state (flags, relationship values) that affect later dialogue.
• Use to decide between Ink, Yarn Spinner, and a custom JSON/resource format.
• Use to wire a dialogue script into your game loop (advance line, present choices, run commands, resolve variables).

When not to use: for engine UI (text boxes, portraits, choice buttons), use godot-ui-control or the engine's UI skill. For persisting narrative variables across sessions, use save-systems. For data-as-resources in Godot/Unity, see godot-resources / unity-scriptableobjects.

Core workflow

1. Choose the authoring approach.
   • Ink — prose-first, writer-friendly, weave/gather flow; great for dialogue-heavy or CYOA narrative. Integrate via ink runtime / inkle plugins.
   • Yarn Spinner — node-based, explicit <<commands>>, strong for game-driven dialogue with lots of engine hooks.
   • Custom runner — a JSON/resource graph + a small interpreter when you need full control or minimal dependencies. Don't build a language; build a graph.
2. Define the node contract. A node yields one of: a line (speaker + text), a set of choices, a command/side-effect, or an end/jump. The runner advances through nodes and hands lines/choices to the UI.
3. Separate variables from flow. Keep a variable store (booleans, numbers, strings) the dialogue reads/writes; gate choices with conditions over it.
4. Localize from the start. Author with line IDs, not raw strings, so the displayed text comes from a string table keyed by locale.
5. Drive it from the game loop. The runner is a state machine: current node → emit content → wait for input (continue or choice) → advance.
6. Verify by walking branches. Exercise each choice path; confirm conditions, variable writes, and that every branch reaches an end or a valid jump.

Patterns

1. Engine-neutral dialogue graph (data, not code)

{
  "start": "guard_intro",
  "nodes": {
    "guard_intro": {
      "speaker": "Guard", "line": "DLG_GUARD_001",
      "choices": [
        { "text": "DLG_OPT_BRIBE", "to": "bribe", "if": "gold >= 50" },
        { "text": "DLG_OPT_LEAVE", "to": "end" }
      ]
    },
    "bribe": {
      "speaker": "Guard", "line": "DLG_GUARD_BRIBED",
      "set": { "gate_open": true, "gold": "gold - 50" },
      "next": "end"
    },
    "end": { "end": true }
  }
}

line/text are string-table IDs (localization), not literal text. if gates a choice; set mutates the variable store. The full interpreter that walks this graph is in references/runner.md.

2. Runner step (a state machine over the graph)

# The runner holds the current node and a variable store; the UI calls advance().
func present(node):
    if node.has("line"):
        ui.show_line(node.speaker, localize(node.line))
    if node.has("choices"):
        var shown = node.choices.filter(func(c): return eval_cond(c.get("if", "")))
        ui.show_choices(shown)            # only choices whose condition passes

func choose(choice):                       # called when the player clicks a choice
    apply_set(choice.get("set", {}))       # write variables
    goto(choice.to)

func goto(id):
    current = graph.nodes[id]
    apply_set(current.get("set", {}))
    if current.get("end", false): ui.close(); return
    present(current)
    if current.has("next") and not current.has("choices"):
        goto(current.next)                 # auto-advance linear nodes

3. Ink — branching with knots, choices, and variables (inkle)

// Ink: '*' = once-only choice, '+' = sticky. [bracketed] text shows only in the
// choice, not the printed result. '->' diverts; '-> END' stops the flow.
VAR gold = 60

=== guard_intro ===
The guard blocks the gate.
* {gold >= 50} [Offer 50 gold]   "Here, take it."
    ~ gold = gold - 50
    The guard pockets it and steps aside. -> END
* [Leave]   You turn back. -> END

Ink tracks how often each knot was seen, so {visited_knot} is a built-in condition. Variables are global (VAR) or temporary (~ temp).

4. Yarn Spinner — nodes, options, and commands (Yarn Spinner 3.x)

title: GuardIntro
---
<<declare $gold = 60>>
<<declare $gate_open = false>>

Yarn lines may start with `Speaker:`; options use `->`; `<<set>>`/`<<declare>>`
manage `$variables`; `<<if>>` gates an option; `<<jump NodeName>>` moves between
nodes. Interpolate values in text with `{$gold}`. Declare every variable before first
use: an undeclared one still compiles (Yarn infers its type and a zero/false/empty
start value), but that hides typos. These constructs are unchanged from Yarn Spinner 2.x.

## Pitfalls

- **Hardcoding display strings** instead of line IDs makes localization a
  rewrite. Author against a string table from day one.
- **Inventing a scripting language** for a simple branching tree. If you only
  need lines + choices + flags, a JSON/resource graph plus a 50-line runner beats
  a parser you must maintain. Use Ink/Yarn when writers need real flow control.
- **Variables coupled to the UI**: store narrative state separately so the same
  dialogue works in cutscenes, menus, and tests. Persist it via `save-systems`.
- **Unreachable or dead-end nodes**: a node with no `next`, choices, or end
  silently stalls. Validate that every node terminates or branches.
- **Mutating state in a line node the player can revisit** double-applies (`gold`
  drained twice). Apply `set` on the transition, or guard with a seen-flag.
- **Mixing Ink's `*` (once-only) and `+` (sticky)** by accident: looped menus
  need sticky `+` choices or the options vanish after one use.

## References

- `references/ink-and-yarn.md` — side-by-side syntax cheat sheet (choices,
  diverts/jumps, variables, conditions, includes) and integration notes.
- `references/runner.md` — a complete custom dialogue runner: graph schema,
  condition/expression evaluation, variable store, and localization lookup.

## Related skills

- `save-systems` — persist narrative variables and seen-flags.
- `godot-resources`, `unity-scriptableobjects` — store dialogue as engine data.
- `godot-ui-control` — render text boxes, portraits, and choice buttons.
- `visual-novel`, `rpg` — genres that compose this skill.