feat(core): pillars — PillarPlacer decorator + Tile::Pillar

A finishing decorator that scatters free-standing pillar columns into larger
rooms on a spaced interior grid. Sixth pass in the dungeon recipe.

- New Tile::Pillar (impassable like Wall, drawn distinctly). Exhaustive matches
  updated: ascii ('o'), frozen macroquad viz (still compiles), wasm code 3.
- PillarPlacer/PillarConfig (room_chance, min_room, spacing): places isolated
  single-cell pillars only on interior room floor (>= 2 from the edge, never the
  center), on a grid with spacing >= 2 — so the floor stays 4-connected by
  construction and a room is never orphaned. Respects non-rect room shapes
  (pillars land only on actual carved floor).
- DungeonConfig gains `pillars`; recipe appends PillarPlacer after DoorPlacer.
- Renderer draws pillars as lit stone columns with a contact shadow; new
  "pillars" density slider.

Core: 121 tests green (5 new: interior-only placement, floor stays connected,
zero-chance/small-room skip, determinism). clippy clean (core + viz).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

reikhelm-core/src/ascii.rs

@@ -24,6 +24,7 @@ const fn glyph(tile: Tile) -> char {
         Tile::Wall => '#',
         Tile::Floor => '.',
         Tile::Door => '+',
+        Tile::Pillar => 'o',
     }
 }
 

reikhelm-core/src/map.rs

@@ -29,6 +29,10 @@ pub enum Tile {
     Floor,
     /// A doorway between regions (walkable, but semantically a threshold).
     Door,
+    /// A free-standing pillar: an impassable column carved into open floor by a
+    /// decorator. Not walkable (treated like [`Tile::Wall`] for movement), but
+    /// semantically distinct so renderers can draw it as a column on lit floor.
+    Pillar,
 }
 
 /// The generator's output: what occupies each cell, the semantic regions, and

reikhelm-core/src/passes/mod.rs

@@ -37,3 +37,6 @@ pub use corridor::CorridorCarver;
 
 pub mod door;
 pub use door::{DoorConfig, DoorPlacer};
+
+pub mod pillar;
+pub use pillar::{PillarConfig, PillarPlacer};

reikhelm-core/src/passes/pillar.rs

@@ -0,0 +1,238 @@
+//! The [`PillarPlacer`] decorator pass.
+//!
+//! A *decorator* is a finishing pass: it embellishes an already-carved,
+//! already-connected map without changing its topology. `PillarPlacer` drops
+//! free-standing [`Pillar`](crate::map::Tile::Pillar) columns into the interior
+//! of larger rooms, on a regularly spaced grid, to give halls the look of a
+//! pillared chamber.
+//!
+//! ## Connectivity is preserved by construction
+//!
+//! Pillars are placed as **isolated single cells** on a grid with spacing `>= 2`
+//! and only in the room *interior* — never within two cells of the room's
+//! bounding edge, and never on the room center. Because every pillar is a lone
+//! obstacle with open floor on all four sides (the grid leaves at least one
+//! floor cell between pillars), the room's floor stays fully 4-connected: you
+//! can always walk around any pillar. So this pass, which runs last in the
+//! dungeon recipe (after [`DoorPlacer`](crate::passes::door::DoorPlacer)), cannot
+//! orphan a room — a property its tests assert directly.
+//!
+//! Pillars land **only on cells that are currently [`Floor`](crate::map::Tile::Floor)**
+//! and that belong to a room's carved `cells`, so they respect non-rectangular
+//! room shapes (a pillar never appears outside the actual carved floor) and never
+//! overwrite a [`Door`](crate::map::Tile::Door) or a corridor.
+
+use serde::{Deserialize, Serialize};
+
+use crate::map::Tile;
+use crate::pass::{GenContext, Pass};
+use crate::region::RegionKind;
+use crate::rng::Rng;
+
+/// Configuration for a [`PillarPlacer`] pass.
+#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
+pub struct PillarConfig {
+    /// Probability that a qualifying (large enough) room is given pillars.
+    /// Clamped to `[0.0, 1.0]`; `0.0` places none.
+    pub room_chance: f64,
+    /// Minimum room extent (the smaller of width/height, in cells) for a room to
+    /// qualify for pillars. Small rooms are left clear.
+    pub min_room: i32,
+    /// Grid spacing between pillars, in cells. Clamped to `>= 2` so pillars never
+    /// form a solid block (which is what keeps the floor 4-connected).
+    pub spacing: i32,
+}
+
+impl Default for PillarConfig {
+    /// A sensible default: a little over half of large rooms (min extent >= 7)
+    /// get a grid of pillars spaced 3 cells apart.
+    fn default() -> Self {
+        PillarConfig {
+            room_chance: 0.55,
+            min_room: 7,
+            spacing: 3,
+        }
+    }
+}
+
+/// A pillar-placing decorator pass.
+///
+/// Construct one with [`PillarPlacer::new`]; it implements [`Pass`] with the
+/// stable name `"pillar_placer"`.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct PillarPlacer {
+    cfg: PillarConfig,
+}
+
+impl PillarPlacer {
+    /// Creates a pillar placer with the given configuration.
+    pub fn new(cfg: PillarConfig) -> Self {
+        PillarPlacer { cfg }
+    }
+}
+
+impl Pass for PillarPlacer {
+    fn name(&self) -> &str {
+        "pillar_placer"
+    }
+
+    fn apply(&self, ctx: &mut GenContext, rng: &mut Rng) {
+        let spacing = self.cfg.spacing.max(2);
+        let off = spacing / 2; // phase the grid so it sits off the room edges
+
+        // Visit rooms in id order. Collect each room's (bounds, cells) first so we
+        // can mutate the grid without holding a borrow on `ctx.regions`.
+        let rooms: Vec<(crate::geometry::Rect, Vec<crate::geometry::Point>)> = ctx
+            .regions
+            .iter()
+            .filter(|r| r.kind == RegionKind::Room && !r.cells.is_empty())
+            .map(|r| (r.bounds, r.cells.clone()))
+            .collect();
+
+        for (b, cells) in rooms {
+            // Only larger rooms qualify; non-qualifying rooms draw no randomness.
+            if b.w.min(b.h) < self.cfg.min_room {
+                continue;
+            }
+            // One coin per qualifying room decides whether it gets pillars.
+            if !rng.chance(self.cfg.room_chance) {
+                continue;
+            }
+
+            let center = b.center();
+            for p in cells {
+                let lx = p.x - b.x;
+                let ly = p.y - b.y;
+                // Keep a clear 2-cell border inside the room and skip the center.
+                if lx < 2 || ly < 2 || lx > b.w - 3 || ly > b.h - 3 || p == center {
+                    continue;
+                }
+                // Place on the spaced grid, but only on actual room floor (so the
+                // pattern respects the room's shape and never hits a door).
+                if (lx - off).rem_euclid(spacing) == 0
+                    && (ly - off).rem_euclid(spacing) == 0
+                    && ctx.tiles.get(p) == Some(&Tile::Floor)
+                {
+                    ctx.tiles.set(p, Tile::Pillar);
+                }
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::blackboard::Blackboard;
+    use crate::geometry::{Point, Rect};
+    use crate::grid::Grid;
+    use crate::region::{ConnGraph, RegionId};
+    use std::collections::BTreeSet;
+
+    /// Builds a context with a single rectangular room carved into Floor — the
+    /// post-RoomCarver state a decorator would see, constructed by hand.
+    fn ctx_with_room(w: u32, h: u32, room: Rect) -> GenContext {
+        let mut ctx = GenContext {
+            tiles: Grid::new(w, h, Tile::Wall),
+            regions: Vec::new(),
+            graph: ConnGraph::new(),
+            blackboard: Blackboard::new(),
+        };
+        let cells: Vec<Point> = room.iter().collect();
+        for &p in &cells {
+            ctx.tiles.set(p, Tile::Floor);
+        }
+        ctx.add_region(RegionKind::Room, room, cells);
+        ctx
+    }
+
+    fn run(ctx: &mut GenContext, cfg: PillarConfig, seed: u64) {
+        let mut rng = Rng::from_seed(seed).fork("pillar_placer#0");
+        PillarPlacer::new(cfg).apply(ctx, &mut rng);
+    }
+
+    fn pillar_count(ctx: &GenContext) -> usize {
+        ctx.tiles.iter().filter(|&(_, &t)| t == Tile::Pillar).count()
+    }
+
+    #[test]
+    fn name_is_pillar_placer() {
+        assert_eq!(PillarPlacer::new(PillarConfig::default()).name(), "pillar_placer");
+    }
+
+    /// With `room_chance = 1.0` a large room gets pillars; every pillar sits on
+    /// former floor, inside the 2-cell border, and not on the center.
+    #[test]
+    fn places_pillars_only_on_interior_floor() {
+        let room = Rect::new(0, 0, 16, 12);
+        let mut ctx = ctx_with_room(16, 12, room);
+        run(&mut ctx, PillarConfig { room_chance: 1.0, min_room: 7, spacing: 3 }, 42);
+
+        assert!(pillar_count(&ctx) > 0, "a 16x12 room should receive pillars");
+        let center = room.center();
+        for (p, &t) in ctx.tiles.iter() {
+            if t == Tile::Pillar {
+                let (lx, ly) = (p.x - room.x, p.y - room.y);
+                assert!(lx >= 2 && ly >= 2 && lx <= room.w - 3 && ly <= room.h - 3,
+                    "pillar at {p:?} is inside the clear border");
+                assert_ne!(p, center, "the room center stays clear");
+            }
+        }
+    }
+
+    /// The room floor (Floor|Door) stays 4-connected after pillars are placed —
+    /// pillars never wall off part of a room.
+    #[test]
+    fn pillars_keep_room_floor_connected() {
+        let room = Rect::new(0, 0, 18, 14);
+        let mut ctx = ctx_with_room(18, 14, room);
+        run(&mut ctx, PillarConfig { room_chance: 1.0, min_room: 7, spacing: 3 }, 7);
+
+        // Total walkable floor cells remaining.
+        let floor: BTreeSet<(i32, i32)> = ctx
+            .tiles
+            .iter()
+            .filter(|&(_, &t)| t == Tile::Floor)
+            .map(|(p, _)| (p.x, p.y))
+            .collect();
+        assert!(!floor.is_empty());
+
+        // Flood from any one floor cell; it must reach all of them.
+        let start = *floor.iter().next().unwrap();
+        let mut seen = BTreeSet::new();
+        let mut stack = vec![start];
+        while let Some((x, y)) = stack.pop() {
+            if !floor.contains(&(x, y)) || !seen.insert((x, y)) {
+                continue;
+            }
+            stack.extend([(x + 1, y), (x - 1, y), (x, y + 1), (x, y - 1)]);
+        }
+        assert_eq!(seen.len(), floor.len(), "pillars must leave the floor 4-connected");
+    }
+
+    /// `room_chance = 0.0` places no pillars; a small room never qualifies.
+    #[test]
+    fn zero_chance_and_small_rooms_get_no_pillars() {
+        let big = Rect::new(0, 0, 16, 12);
+        let mut ctx = ctx_with_room(16, 12, big);
+        run(&mut ctx, PillarConfig { room_chance: 0.0, min_room: 7, spacing: 3 }, 99);
+        assert_eq!(pillar_count(&ctx), 0, "room_chance 0.0 places nothing");
+
+        let small = Rect::new(0, 0, 6, 6);
+        let mut ctx2 = ctx_with_room(6, 6, small);
+        run(&mut ctx2, PillarConfig { room_chance: 1.0, min_room: 7, spacing: 3 }, 99);
+        assert_eq!(pillar_count(&ctx2), 0, "a room below min_room gets none");
+    }
+
+    /// Same seed reproduces the same pillar layout.
+    #[test]
+    fn pillars_are_deterministic() {
+        let room = Rect::new(0, 0, 16, 12);
+        let cfg = PillarConfig::default();
+        let mut a = ctx_with_room(16, 12, room);
+        let mut b = ctx_with_room(16, 12, room);
+        run(&mut a, cfg, 0x5EED);
+        run(&mut b, cfg, 0x5EED);
+        assert_eq!(a.tiles, b.tiles);
+    }
+}

reikhelm-core/src/recipes/dungeon.rs

@@ -6,7 +6,7 @@
 //! order:
 //!
 //! ```text
-//! BspPartition → RoomCarver → MstConnect → CorridorCarver → DoorPlacer
+//! BspPartition → RoomCarver → MstConnect → CorridorCarver → DoorPlacer → PillarPlacer
 //! ```
 //!
 //! 1. [`BspPartition`] cuts the canvas into leaf rectangles (one placeholder
@@ -17,6 +17,8 @@
 //! 4. [`CorridorCarver`] carves an L-shaped floor corridor per planned edge.
 //! 5. [`DoorPlacer`] marks a fraction of the room↔corridor pierce points as
 //!    doors (purely cosmetic — connectivity is already established by the floor).
+//! 6. [`PillarPlacer`] scatters free-standing pillars into larger rooms (a
+//!    finishing decorator; isolated obstacles that never break connectivity).
 //!
 //! ## Why validation matters (spec §8)
 //!
@@ -39,7 +41,7 @@ use serde::{Deserialize, Serialize};
 use crate::pass::Pipeline;
 use crate::passes::{
     BspConfig, BspPartition, ConnectConfig, CorridorCarver, DoorConfig, DoorPlacer, MstConnect,
-    RoomCarver, RoomConfig, ShapeWeights,
+    PillarConfig, PillarPlacer, RoomCarver, RoomConfig, ShapeWeights,
 };
 
 /// Configuration for the [`dungeon`] recipe.
@@ -62,6 +64,8 @@ pub struct DungeonConfig {
     pub connect: ConnectConfig,
     /// How room↔corridor pierce points are marked as doors.
     pub doors: DoorConfig,
+    /// How free-standing pillars are scattered into larger rooms (decorator).
+    pub pillars: PillarConfig,
 }
 
 impl Default for DungeonConfig {
@@ -96,6 +100,7 @@ impl Default for DungeonConfig {
                 extra_edge_ratio: 0.30,
             },
             doors: DoorConfig::default(),
+            pillars: PillarConfig::default(),
         }
     }
 }
@@ -206,7 +211,8 @@ pub fn dungeon(cfg: DungeonConfig) -> Result<Pipeline, ConfigError> {
         .then(RoomCarver::new(cfg.rooms))
         .then(MstConnect::new(cfg.connect))
         .then(CorridorCarver::new())
-        .then(DoorPlacer::new(cfg.doors));
+        .then(DoorPlacer::new(cfg.doors))
+        .then(PillarPlacer::new(cfg.pillars));
 
     Ok(pipeline)
 }
@@ -219,13 +225,14 @@ mod tests {
     use crate::region::RegionKind;
     use std::collections::{BTreeSet, VecDeque};
 
-    /// The five pass names in pipeline order, used to check snapshot labels.
-    const PASS_NAMES: [&str; 5] = [
+    /// The pass names in pipeline order, used to check snapshot labels.
+    const PASS_NAMES: [&str; 6] = [
         "bsp_partition",
         "room_carver",
         "mst_connect",
         "corridor_carver",
         "door_placer",
+        "pillar_placer",
     ];
 
     /// Is `p` a walkable cell (Floor or Door are both walkable; Wall is not)?
@@ -291,7 +298,7 @@ mod tests {
         let (snapped, snapshots) = dungeon(cfg).unwrap().run_with_snapshots(7);
 
         assert_eq!(plain, snapped, "snapshotting must not change the map");
-        assert_eq!(snapshots.len(), 5, "one snapshot per pass (five passes)");
+        assert_eq!(snapshots.len(), 6, "one snapshot per pass (six passes)");
 
         let labels: Vec<&str> = snapshots.iter().map(|s| s.label.as_str()).collect();
         assert_eq!(

reikhelm-viz/src/main.rs

@@ -41,6 +41,7 @@ fn color_of(tile: Tile) -> Color {
         Tile::Wall => Color::new(0.07, 0.07, 0.09, 1.0),
         Tile::Floor => Color::new(0.80, 0.76, 0.66, 1.0),
         Tile::Door => GOLD,
+        Tile::Pillar => Color::new(0.30, 0.28, 0.26, 1.0),
     }
 }
 

reikhelm-wasm/src/lib.rs

@@ -36,6 +36,7 @@ fn tile_code(tile: Tile) -> u8 {
         Tile::Wall => 0,
         Tile::Floor => 1,
         Tile::Door => 2,
+        Tile::Pillar => 3,
     }
 }
 

reikhelm-web/main.js

@@ -40,6 +40,7 @@ const SLIDERS = [
   ['rooms.shapes.octagon', '⬡ octagon', 0, 3, 0.1],
   ['rooms.shapes.ellipse', '◯ ellipse', 0, 3, 0.1],
   ['rooms.shapes.plus', '✚ plus', 0, 3, 0.1],
+  ['pillars.room_chance', 'pillars', 0, 1, 0.05],
 ];
 
 function getPath(obj, path) {

reikhelm-web/render.js

@@ -6,7 +6,7 @@
 // same contract the Rust renderers honor. All art (color, light, depth) lives
 // here; the core stores none of it.
 
-const WALL = 0, FLOOR = 1, DOOR = 2;
+const WALL = 0, FLOOR = 1, DOOR = 2, PILLAR = 3;
 
 // Palette — renderer-owned. Warm stone on near-black, amber thresholds.
 const PAL = {
@@ -19,6 +19,8 @@ const PAL = {
   wallRim: [120, 110, 128], // rim where stone meets carved floor
   doorWarm: [212, 165, 74],
   doorDark: [120, 84, 32],
+  pillarTop: [122, 112, 100], // lit top-left of a stone column
+  pillarBody: [60, 54, 54],   // shadowed lower-right
   outlineRoom: 'rgba(122, 184, 240, 0.85)',
   outlineCorr: 'rgba(150, 150, 170, 0.40)',
   edge: 'rgba(232, 96, 84, 0.85)',
@@ -242,6 +244,29 @@ export function renderMap(ctx, vw, vh, env, opts = {}) {
     }
   }
 
+  // 3.5) Pillars — free-standing stone columns standing on the lit floor (the
+  // floor under them was already painted in pass 1).
+  for (let y = 0; y < h; y++) {
+    for (let x = 0; x < w; x++) {
+      if (tiles[y][x] !== PILLAR) continue;
+      const cxp = px(x) + cell / 2, cyp = py(y) + cell / 2;
+      const r = cell * 0.36;
+      // Contact shadow pooled at the base.
+      ctx.fillStyle = 'rgba(0,0,0,0.45)';
+      ctx.beginPath();
+      ctx.ellipse(cxp, cyp + cell * 0.18, r * 1.05, r * 0.62, 0, 0, Math.PI * 2);
+      ctx.fill();
+      // Column body, lit from the top-left.
+      const grd = ctx.createRadialGradient(cxp - r * 0.4, cyp - r * 0.45, r * 0.1, cxp, cyp, r * 1.1);
+      grd.addColorStop(0, rgb(PAL.pillarTop));
+      grd.addColorStop(1, rgb(PAL.pillarBody));
+      ctx.fillStyle = grd;
+      ctx.beginPath();
+      ctx.arc(cxp, cyp, r, 0, Math.PI * 2);
+      ctx.fill();
+    }
+  }
+
   // 4) Vignette over the whole grid for mood.
   if (lit && LIGHT.vignette > 0) {
     const cxp = ox + gw / 2, cyp = oy + gh / 2;