level-design

The full skill.

Original instructions from the publisher’s SKILL.md

# Level design

A level is a **sequence of intentional experiences** delivered through space.
Good level design is a *process*: define the metrics movement is built on, block
out geometry with primitives, play it, then dress it — never the reverse. This
skill is the engine-neutral practice; use `godot-tilemap`/`unity-tilemap-2d` to
lay out 2D grids and gridmaps for 3D.

## When to use

- Use to plan a level's structure: critical path, pacing, gating, encounters,
  and where the player learns vs is tested.
- Use the **blockout → test → iterate → dress** workflow to build a level that
  plays well before any art exists.
- Use to derive level **metrics** from the character's movement so geometry is
  reachable and fair.

**When *not* to use:** to *generate* levels algorithmically, use `procedural-gen`
(authored and procedural design are complementary). For the engine's tile/grid
painting tools, use `godot-tilemap` / `unity-tilemap-2d`. For the movement
abilities the metrics come from, that's the engine movement skill + `input-systems`.

## Core workflow

1. **Derive metrics first.** Measure the character: max jump height and distance,
   run speed, reach, camera range. Every gap, ledge, and corridor is sized in
   these units. Lock them before building geometry.
2. **Blockout (whitebox/greybox).** Build the whole level from untextured
   primitives at correct scale. Validate flow, sightlines, and reachability while
   changes are cheap. No art yet.
3. **Define the critical path** (start → goal) and the **golden path** you expect
   most players to take. Layer optional/secret paths off it.
4. **Pace the experience.** Alternate tension and rest in a deliberate curve;
   don't run combat-combat-combat. Give the player room to breathe and to
   anticipate.
5. **Teach, then test.** Introduce each mechanic in a safe space, let the player
   practice, then test it under pressure. Difficulty rises in a sawtooth, not a
   straight line.
6. **Gate with intent.** Use locks/keys, abilities, and one-way drops to control
   order and pacing; guide with light, lines, and landmarks rather than walls.
7. **Playtest and iterate.** Watch real players: where do they get lost, stuck,
   bored, or killed unfairly? Fix the blockout; only dress when it plays well.

## Patterns

### 1. Player metrics drive every dimension

```gdscript
# Measure the character ONCE, then size geometry in these units. If the jump
# changes, gaps must be re-derived — never eyeball reachability.
const RUN_SPEED      := 240.0   # px/s (or m/s in 3D)
const MAX_JUMP_H     := 96.0    # peak height of a full jump
const MAX_JUMP_DIST  := 200.0   # horizontal distance of a running jump
const SAFE_GAP       := MAX_JUMP_DIST * 0.7   # comfortable, not pixel-perfect
const HARD_GAP       := MAX_JUMP_DIST * 0.95  # a deliberate skill check
# Build platforms so required jumps use SAFE_GAP; reserve HARD_GAP for optional reward.
```

A reachable level falls out of honest metrics. A platform placed `MAX_JUMP_DIST +
1` away is impossible; one at `SAFE_GAP` is fair. Keep these constants beside the
level data so designers and code agree.

### 2. Encounter / pacing as data (a tension timeline)

```gdscript
# Author the level as a sequence of beats with an intended intensity (0..1).
# This makes the pacing curve explicit and reviewable before you build rooms.
const BEATS := [
    { "room": "entry",      "type": "teach",   "intensity": 0.1 },
    { "room": "hall_1",     "type": "combat",  "intensity": 0.5 },
    { "room": "vista",      "type": "rest",    "intensity": 0.1 },  # breather + reward
    { "room": "gauntlet",   "type": "combat",  "intensity": 0.8 },
    { "room": "save_room",  "type": "rest",    "intensity": 0.2 },  # before the boss
    { "room": "boss",       "type": "climax",  "intensity": 1.0 },
]
# Read the intensity column top-to-bottom: it should rise overall but dip for rests
# (a sawtooth), never flatline high. Drive spawns/music intensity from this.
```

### 3. Gating and the critical path (a small graph)

```gdscript
# Model the level as rooms + gated connections. Validate that the goal is
# reachable with the keys/abilities the player can actually obtain in order.
const ROOMS := {
    "entry":   { "exits": [ { "to": "hall_1" } ] },
    "hall_1":  { "exits": [ { "to": "vista", "needs": "double_jump" },
                            { "to": "side_room" } ] },           # optional branch
    "side_room": { "exits": [ { "to": "hall_1" } ], "grants": "double_jump" },
    "vista":   { "exits": [ { "to": "boss", "needs": "red_key" } ] },
}
# Validation (do this!): from "entry", can the player reach "boss" given that
# "double_jump" is granted in "side_room" before "vista" requires it? A flood
# fill that only traverses an exit when its `needs` is already satisfiable
# proves the critical path isn't soft-locked.
```

## Pitfalls

- **Dressing before it plays.** Detailing a blockout you haven't validated wastes
  the most expensive work on a layout you'll change. Greybox and test first.
- **Geometry that ignores metrics**: gaps the jump can't clear, ledges below
  reach, corridors narrower than the camera needs. Size everything in player units.
- **Flat pacing.** Wall-to-wall combat (or wall-to-wall calm) numbs the player.
  Alternate tension and rest; place a breather and a save before the climax.
- **Testing a mechanic before teaching it.** Players meet a hazard for the first
  time in a lethal spot. Introduce safely, let them practice, then test.
- **Soft-locks and dead ends.** A gate needs an ability/key obtainable only past
  the gate. Validate the critical path's key/ability order, not just connectivity.
- **No readability / guidance.** Players get lost when nothing draws the eye. Use
  light, leading lines, color, and landmarks to point toward the path.
- **One-way drops with no signposting** strand or surprise players. Telegraph
  irreversible moves.
- **Confusing procedural with authored.** Generation gives variety, not
  authored pacing. Use `procedural-gen` for variety; hand-author for intent.

## References

- `references/pacing-and-flow.md` — the difficulty/tension curve in depth,
  teaching-loop design (introduce→develop→twist→test), readability and guidance
  techniques, 2D vs 3D layout considerations, and a blockout review checklist.

## Related skills

- `godot-tilemap`, `unity-tilemap-2d` — paint 2D level grids; gridmaps for 3D.
- `procedural-gen` — generate variety to complement authored structure.
- `game-ai` — encounter enemies that navigate the space you build.
- `platformer`, `puzzle`, `roguelike` — genres that compose this skill.