Merge branch 'fix/issue-52'

src/game/wilderness.ts

@@ -70,11 +70,12 @@
  * set to the packed value `0x40002` (`bIsFloor` plus a wall-layer bit) and the
  * actual DT1 style/sequence is then chosen at runtime by a rarity roll inside
  * `DRLGROOMTILE_GetTileCache`, against the libraries selected by the level type's
- * hardcoded `dwDt1Mask`. That roll cannot be reproduced from the shipped tables,
+ * hardcoded `dwDt1Mask`. This port supports multi-DT1 weighted ground tile blending
- * so this port takes the ground tile from the level's own border pieces instead
+ * via `fillGround` using `dwDt1Mask` / `RarityFrameIndex` or candidate ground tiles,
- * — see {@link WildernessRequest.groundTile}.
+ * with single-tile fallback for backward compatibility — see {@link WildernessRequest.groundTile}.
  */
 import type { Ds1, Ds1Cell, Ds1Floor, Ds1Object, Ds1Wall, Ds1Substitution } from '../formats/ds1.ts'
+import type { Dt1 } from '../formats/dt1.ts'
 import { Rng } from './rng.ts'
 import { SUB_TILES_PER_TILE } from './map.ts'
 import type { Side } from './world-graph.ts'
@@ -217,15 +218,24 @@ export interface WildernessRequest {
   readonly specialPresets?: readonly string[]
   /**
    * The ground tile to lay under everything, as a DT1 `style`/`sequence` pair.
+   * Can also accept an array of {@link WeightedGroundTile} candidates for multi-tile blending.
    *
    * The shipped game leaves this to a runtime rarity roll over the DT1 libraries
    * the level type's mask selects, which no table records. When omitted,
-   * {@link generateWilderness} derives it from the level's own pieces as the most
+   * {@link generateWilderness} derives it from the level's own pieces or DT1 libraries,
-   * common floor a border piece uses outside the piece's own wall ring — the
+   * recording the choice in `stats.groundTile` (and `stats.groundTiles`).
-   * outdoor ground those pieces sit on — and records the choice in
-   * `stats.groundTile`.
    */
-  readonly groundTile?: { readonly style: number; readonly sequence: number }
+  readonly groundTile?: { readonly style: number; readonly sequence: number } | readonly WeightedGroundTile[]
+  /**
+   * Array of candidate ground tiles with relative weights for multi-tile ground blending.
+   * When provided, `fillGround` blends these tiles across the canvas.
+   */
+  readonly groundTiles?: readonly WeightedGroundTile[]
+  /**
+   * DT1 libraries loaded for the level. When supplied without explicit groundTile(s),
+   * candidate ground tiles are derived using dwDt1Mask and RarityFrameIndex.
+   */
+  readonly dt1Libraries?: readonly Dt1[]
   /**
    * Explicit block-grid size, for the levels `Levels.txt` leaves unset.
    *
@@ -296,6 +306,18 @@ export const CANONICAL_GROUND_TILES: Readonly<Record<string, { readonly style: n
   'Act 5 - Barricade': { style: 0, sequence: 0 },
 }
 
+/** Canonical default open ground floor tile pools per wilderness level type. */
+export const CANONICAL_GROUND_POOLS: Readonly<Record<string, readonly WeightedGroundTile[]>> = {
+  'Act 1 - Wilderness': [{ style: 0, sequence: 0, weight: 1 }],
+  'Act 2 - Desert': [{ style: 0, sequence: 1, weight: 1 }],
+  'Act 3 - Jungle': [{ style: 0, sequence: 0, weight: 1 }],
+  'Act 3 - Kurast': [{ style: 0, sequence: 0, weight: 1 }],
+  'Act 4 - Mesa': [{ style: 10, sequence: 0, weight: 1 }],
+  'Act 4 - Lava': [{ style: 20, sequence: 3, weight: 1 }],
+  'Act 5 - Siege': [{ style: 0, sequence: 0, weight: 1 }],
+  'Act 5 - Barricade': [{ style: 0, sequence: 0, weight: 1 }],
+}
+
 /* ------------------------------------------------------------------------- *
  * Classification
  * ------------------------------------------------------------------------- */
@@ -475,30 +497,317 @@ export function stampDs1(canvas: Canvas, source: Ds1, originX: number, originY:
   return written
 }
 
+/** A candidate ground tile with an optional weighting/rarity. */
+export interface WeightedGroundTile {
+  readonly style: number
+  readonly sequence: number
+  /**
+   * Relative selection weight (e.g. from `RarityFrameIndex` or piece counts).
+   * Defaults to 1 (or `rarityFrameIndex`) if omitted or <= 0.
+   */
+  readonly weight?: number
+  /**
+   * Direct DT1 `rarityFrameIndex`, if sourced from a DT1 tile.
+   */
+  readonly rarityFrameIndex?: number
+}
+
+/** Configuration options for ground tile blending. */
+export interface FillGroundOptions {
+  /** PRNG seed or Rng instance for deterministic tile generation. */
+  readonly seed?: number | Rng
+  /** Blending mode: 'cdf' (cell-by-cell weighted draw) or 'spatial' (coherent noise patches). Default: 'spatial'. */
+  readonly mode?: 'cdf' | 'spatial'
+  /** Spatial noise scale in cells (default: 6). Higher values produce broader patches. */
+  readonly spatialScale?: number
+  /** Weight of spatial coherence vs cell jitter in [0, 1] (default: 0.6). */
+  readonly spatialCoherence?: number
+}
+
 /**
- * Write one floor tile into every cell of a rectangle.
+ * Fast, high-quality 32-bit integer hash for 2D coordinates and a seed.
+ * Returns a uniform pseudo-random number in [0, 1).
+ */
+export function cellHash(x: number, y: number, seed: number): number {
+  let h = (seed ^ Math.imul(x, 0x1b873593) ^ Math.imul(y, 0x85ebca6b)) >>> 0
+  h = Math.imul(h ^ (h >>> 16), 0x45d9f3b) >>> 0
+  h = Math.imul(h ^ (h >>> 16), 0x45d9f3b) >>> 0
+  h = (h ^ (h >>> 16)) >>> 0
+  return h / 4294967296
+}
+
+/**
+ * 2D smooth value noise with cubic Hermite interpolation.
+ * Returns a value in [0, 1).
+ */
+export function smoothNoise2D(x: number, y: number, scale: number, seed: number): number {
+  const invScale = 1 / Math.max(1, scale)
+  const gx = Math.floor(x * invScale)
+  const gy = Math.floor(y * invScale)
+  const fx = x * invScale - gx
+  const fy = y * invScale - gy
+
+  // Cubic Hermite smoothstep: 3t^2 - 2t^3
+  const sx = fx * fx * (3 - 2 * fx)
+  const sy = fy * fy * (3 - 2 * fy)
+
+  const n00 = cellHash(gx, gy, seed)
+  const n10 = cellHash(gx + 1, gy, seed)
+  const n01 = cellHash(gx, gy + 1, seed)
+  const n11 = cellHash(gx + 1, gy + 1, seed)
+
+  const nx0 = n00 + sx * (n10 - n00)
+  const nx1 = n01 + sx * (n11 - n01)
+  return nx0 + sy * (nx1 - nx0)
+}
+
+function isTileArray(
+  val: unknown,
+): val is readonly unknown[] {
+  return Array.isArray(val)
+}
+
+/**
+ * Sample a single ground tile at (x, y) from weighted candidate tiles.
+ */
+export function sampleGroundTile(
+  tileOrTiles: WeightedGroundTile | readonly WeightedGroundTile[],
+  x: number,
+  y: number,
+  optionsOrSeed?: number | Rng | FillGroundOptions,
+): WeightedGroundTile {
+  if (!isTileArray(tileOrTiles)) return tileOrTiles
+  if (tileOrTiles.length === 0) return { style: 0, sequence: 0 }
+  const tiles = tileOrTiles as readonly WeightedGroundTile[]
+  if (tiles.length === 1) return tiles[0]!
+
+  let seed = 0
+  let mode: 'cdf' | 'spatial' = 'spatial'
+  let spatialScale = 6
+  let spatialCoherence = 0.6
+
+  if (typeof optionsOrSeed === 'number') {
+    seed = optionsOrSeed >>> 0
+  } else if (optionsOrSeed instanceof Rng) {
+    seed = optionsOrSeed.seed >>> 0
+  } else if (optionsOrSeed && typeof optionsOrSeed === 'object') {
+    if (typeof optionsOrSeed.seed === 'number') seed = optionsOrSeed.seed >>> 0
+    else if (optionsOrSeed.seed instanceof Rng) seed = optionsOrSeed.seed.seed >>> 0
+    if (optionsOrSeed.mode !== undefined) mode = optionsOrSeed.mode
+    if (typeof optionsOrSeed.spatialScale === 'number' && optionsOrSeed.spatialScale > 0) {
+      spatialScale = optionsOrSeed.spatialScale
+    }
+    if (typeof optionsOrSeed.spatialCoherence === 'number') {
+      spatialCoherence = Math.max(0, Math.min(1, optionsOrSeed.spatialCoherence))
+    }
+  }
+
+  const valid = tileOrTiles.filter(t => {
+    const w = t.weight !== undefined ? t.weight : t.rarityFrameIndex !== undefined ? t.rarityFrameIndex : 1
+    return w > 0
+  })
+  const active = valid.length > 0 ? valid : tileOrTiles
+  if (active.length === 1) return active[0]!
+
+  let totalWeight = 0
+  for (const c of active) {
+    const w = c.weight !== undefined ? c.weight : c.rarityFrameIndex !== undefined ? c.rarityFrameIndex : 1
+    totalWeight += Math.max(0, w)
+  }
+  if (totalWeight <= 0) return active[0]!
+
+  const cdfs: number[] = []
+  let running = 0
+  for (let i = 0; i < active.length; i += 1) {
+    const w = active[i]!.weight !== undefined
+      ? active[i]!.weight!
+      : active[i]!.rarityFrameIndex !== undefined
+        ? active[i]!.rarityFrameIndex!
+        : 1
+    running += Math.max(0, w)
+    cdfs.push(running / totalWeight)
+  }
+  cdfs[cdfs.length - 1] = 1.0
+
+  let u: number
+  if (mode === 'cdf') {
+    u = cellHash(x, y, seed)
+  } else {
+    const smooth = smoothNoise2D(x, y, spatialScale, seed)
+    const jitter = cellHash(x, y, seed ^ 0x9e3779b9)
+    u = spatialCoherence * smooth + (1 - spatialCoherence) * jitter
+  }
+
+  for (let i = 0; i < cdfs.length; i += 1) {
+    if (u < cdfs[i]!) return active[i]!
+  }
+  return active[active.length - 1]!
+}
+
+/**
+ * Write one or more floor tiles into every cell of a rectangle with weighted random blending.
  *
- * Used for the ground. The tile is a bare `style`/`sequence` reference, so it
+ * Supports:
- * resolves against the level type's libraries exactly as a decoded DS1's floor
+ * 1. Single tile fallback (backward compatibility): All cells receive the single tile.
- * would; the wall layers are left empty, which is what makes the ground walkable.
+ * 2. Multi-tile weighted distribution: Tiles are sampled via CDF sampling or spatial noise,
+ *    naturally blending variations (e.g. pure grass, pebbled dirt, weeds) across the ground
+ *    without jarring discontinuities.
  *
  * @param canvas - the canvas.
- * @param tile - the floor reference.
+ * @param tileOrTiles - single tile or array of weighted candidate tiles.
  * @param x - left edge in cells.
  * @param y - top edge in cells.
  * @param width - cells.
  * @param height - cells.
+ * @param optionsOrSeed - PRNG seed, Rng instance, or blending options.
  * @returns the number of cells written.
  */
 export function fillGround(
   canvas: Canvas,
-  tile: { style: number; sequence: number },
+  tileOrTiles: WeightedGroundTile | readonly WeightedGroundTile[],
   x: number,
   y: number,
   width: number,
   height: number,
+  optionsOrSeed?: number | Rng | FillGroundOptions,
 ): number {
-  let written = 0
+  if (!isTileArray(tileOrTiles)) {
+    const tile = tileOrTiles
+    let written = 0
+    for (let cy = y; cy < y + height; cy += 1) {
+      if (cy < 0 || cy >= canvas.height) continue
+      const row = canvas.cells[cy]!
+      for (let cx = x; cx < x + width; cx += 1) {
+        if (cx < 0 || cx >= canvas.width) continue
+        const cell = row[cx]!
+        const floor = cell.floors[0]
+        if (floor === undefined) continue
+        Object.assign(floor, { prop1: 2, style: tile.style, sequence: tile.sequence, hidden: false })
+        written += 1
+      }
+    }
+    return written
+  }
+
+  if (tileOrTiles.length === 0) return 0
+  const tiles = tileOrTiles as readonly WeightedGroundTile[]
+
+  if (tiles.length === 1) {
+    const tile = tiles[0]!
+    let written = 0
+    for (let cy = y; cy < y + height; cy += 1) {
+      if (cy < 0 || cy >= canvas.height) continue
+      const row = canvas.cells[cy]!
+      for (let cx = x; cx < x + width; cx += 1) {
+        if (cx < 0 || cx >= canvas.width) continue
+        const cell = row[cx]!
+        const floor = cell.floors[0]
+        if (floor === undefined) continue
+        Object.assign(floor, { prop1: 2, style: tile.style, sequence: tile.sequence, hidden: false })
+        written += 1
+      }
+    }
+    return written
+  }
+
+  const validCandidates: { style: number; sequence: number; weight: number }[] = []
+  for (const t of tileOrTiles) {
+    const w = t.weight !== undefined
+      ? Math.max(0, t.weight)
+      : t.rarityFrameIndex !== undefined
+        ? Math.max(0, t.rarityFrameIndex)
+        : 1
+    if (w > 0) {
+      validCandidates.push({ style: t.style, sequence: t.sequence, weight: w })
+    }
+  }
+
+  const active = validCandidates.length > 0
+    ? validCandidates
+    : tileOrTiles.map(t => ({ style: t.style, sequence: t.sequence, weight: 1 }))
+
+  if (active.length === 1) {
+    const tile = active[0]!
+    let written = 0
+    for (let cy = y; cy < y + height; cy += 1) {
+      if (cy < 0 || cy >= canvas.height) continue
+      const row = canvas.cells[cy]!
+      for (let cx = x; cx < x + width; cx += 1) {
+        if (cx < 0 || cx >= canvas.width) continue
+        const cell = row[cx]!
+        const floor = cell.floors[0]
+        if (floor === undefined) continue
+        Object.assign(floor, { prop1: 2, style: tile.style, sequence: tile.sequence, hidden: false })
+        written += 1
+      }
+    }
+    return written
+  }
+
+  let totalWeight = 0
+  for (const c of active) totalWeight += c.weight
+  const cdfThresholds: number[] = []
+  let running = 0
+  for (let i = 0; i < active.length; i += 1) {
+    running += active[i]!.weight
+    cdfThresholds.push(running / totalWeight)
+  }
+  cdfThresholds[cdfThresholds.length - 1] = 1.0
+
+  const pickCandidate = (u: number): { style: number; sequence: number } => {
+    for (let i = 0; i < cdfThresholds.length; i += 1) {
+      if (u < cdfThresholds[i]!) return active[i]!
+    }
+    return active[active.length - 1]!
+  }
+
+  let seed = 0
+  let mode: 'cdf' | 'spatial' = 'spatial'
+  let spatialScale = 6
+  let spatialCoherence = 0.6
+
+  if (typeof optionsOrSeed === 'number') {
+    seed = optionsOrSeed >>> 0
+  } else if (optionsOrSeed instanceof Rng) {
+    seed = optionsOrSeed.seed >>> 0
+  } else if (optionsOrSeed && typeof optionsOrSeed === 'object') {
+    if (typeof optionsOrSeed.seed === 'number') seed = optionsOrSeed.seed >>> 0
+    else if (optionsOrSeed.seed instanceof Rng) seed = optionsOrSeed.seed.seed >>> 0
+    if (optionsOrSeed.mode !== undefined) mode = optionsOrSeed.mode
+    if (typeof optionsOrSeed.spatialScale === 'number' && optionsOrSeed.spatialScale > 0) {
+      spatialScale = optionsOrSeed.spatialScale
+    }
+    if (typeof optionsOrSeed.spatialCoherence === 'number') {
+      spatialCoherence = Math.max(0, Math.min(1, optionsOrSeed.spatialCoherence))
+    }
+  }
+
+  if (mode === 'cdf') {
+    let written = 0
+    for (let cy = y; cy < y + height; cy += 1) {
+      if (cy < 0 || cy >= canvas.height) continue
+      const row = canvas.cells[cy]!
+      for (let cx = x; cx < x + width; cx += 1) {
+        if (cx < 0 || cx >= canvas.width) continue
+        const cell = row[cx]!
+        const floor = cell.floors[0]
+        if (floor === undefined) continue
+        const u = cellHash(cx, cy, seed)
+        const picked = pickCandidate(u)
+        Object.assign(floor, { prop1: 2, style: picked.style, sequence: picked.sequence, hidden: false })
+        written += 1
+      }
+    }
+    return written
+  }
+
+  interface CellEntry {
+    floor: Ds1Floor
+    v: number
+    index: number
+  }
+  const cellsToWrite: CellEntry[] = []
+
   for (let cy = y; cy < y + height; cy += 1) {
     if (cy < 0 || cy >= canvas.height) continue
     const row = canvas.cells[cy]!
@@ -507,13 +816,34 @@ export function fillGround(
       const cell = row[cx]!
       const floor = cell.floors[0]
       if (floor === undefined) continue
-      // `prop1` 2 is the ordinary walkable floor property that the shipped
+      const smooth = smoothNoise2D(cx, cy, spatialScale, seed)
-      // outdoor pieces use; walls stay empty so the sub-tiles are open.
+      const jitter = cellHash(cx, cy, seed ^ 0x9e3779b9)
-      Object.assign(floor, { prop1: 2, style: tile.style, sequence: tile.sequence, hidden: false })
+      const v = spatialCoherence * smooth + (1 - spatialCoherence) * jitter
-      written += 1
+      cellsToWrite.push({
+        floor,
+        v,
+        index: cy * canvas.width + cx,
+      })
     }
   }
-  return written
+
+  if (cellsToWrite.length === 0) return 0
+
+  cellsToWrite.sort((a, b) => (a.v !== b.v ? a.v - b.v : a.index - b.index))
+
+  const totalCells = cellsToWrite.length
+  for (let r = 0; r < totalCells; r += 1) {
+    const u = (r + 0.5) / totalCells
+    const picked = pickCandidate(u)
+    Object.assign(cellsToWrite[r]!.floor, {
+      prop1: 2,
+      style: picked.style,
+      sequence: picked.sequence,
+      hidden: false,
+    })
+  }
+
+  return totalCells
 }
 
 /* ------------------------------------------------------------------------- *
@@ -521,24 +851,74 @@ export function fillGround(
  * ------------------------------------------------------------------------- */
 
 /**
- * Pick the tile the level's own pieces stand on.
+ * Extract candidate ground floor tiles from DT1 libraries filtered by dwDt1Mask.
  *
- * The shipped game picks the ground with a rarity roll over the DT1 libraries
+ * In Diablo II outdoor levels, DRLGROOMTILE_GetTileCache scans the libraries
- * that the level type's hardcoded mask selects (`DRLGROOMTILE_GetTileCache`),
+ * activated by the level type's dwDt1Mask (switch on nLevelType in DRLGOUTDOORS_GenerateLevel).
- * and no table records which tile that lands on. The observable proxy is the
+ * Floor tiles (tile.type === 0) with positive RarityFrameIndex are accumulated
- * pieces themselves: a border or fill DS1 is authored as a chunk of scenery
+ * into candidate ground tiles weighted by their rarity.
- * sitting *on* the outdoor ground, so the floor it uses away from its own outer
- * ring is that ground.
  *
- * The outer ring is excluded because that is where the cliff face and its
+ * @param libraries - All DT1 libraries resolved for the level (in slot order).
- * transition tiles live. Cells with `prop1 == 0` are excluded because they are
+ * @param dt1Mask - The bitmask selecting which DT1 slots are active for ground.
- * unused slots, not tiles. The most frequent survivor wins, ties going to the
+ * @returns Array of weighted ground tiles.
- * first seen so the choice is deterministic.
- *
- * @param pieces - the level's border and fill pieces.
- * @returns the tile, or null when no piece carries any floor.
  */
-function deriveGroundTile(pieces: readonly WildernessPiece[]): { style: number; sequence: number } | null {
+export function deriveGroundTilesFromDt1Libraries(
+  libraries: readonly Dt1[],
+  dt1Mask: number,
+): WeightedGroundTile[] {
+  const counts = new Map<string, { style: number; sequence: number; weight: number }>()
+
+  for (let libIndex = 0; libIndex < libraries.length; libIndex += 1) {
+    if ((dt1Mask & (1 << libIndex)) === 0) continue
+    const lib = libraries[libIndex]
+    if (!lib) continue
+    for (const tile of lib.tiles) {
+      if (tile.type !== 0) continue
+      const rarity = Math.max(0, tile.rarityFrameIndex | 0)
+      if (rarity <= 0) continue
+      const key = `${String(tile.style)}:${String(tile.sequence)}`
+      const existing = counts.get(key)
+      if (existing === undefined) {
+        counts.set(key, { style: tile.style, sequence: tile.sequence, weight: rarity })
+      } else {
+        existing.weight += rarity
+      }
+    }
+  }
+
+  if (counts.size === 0) {
+    for (let libIndex = 0; libIndex < libraries.length; libIndex += 1) {
+      if ((dt1Mask & (1 << libIndex)) === 0) continue
+      const lib = libraries[libIndex]
+      if (!lib) continue
+      for (const tile of lib.tiles) {
+        if (tile.type !== 0) continue
+        const key = `${String(tile.style)}:${String(tile.sequence)}`
+        if (!counts.has(key)) {
+          counts.set(key, { style: tile.style, sequence: tile.sequence, weight: 1 })
+        }
+      }
+    }
+  }
+
+  return Array.from(counts.values()).map(e => ({
+    style: e.style,
+    sequence: e.sequence,
+    weight: e.weight,
+    rarityFrameIndex: e.weight,
+  }))
+}
+
+/**
+ * Derive candidate ground tiles from the level's own border and fill pieces.
+ *
+ * Scans interior cells of each piece variant for visible floor tiles, tallying
+ * their occurrences to use as relative weights.
+ *
+ * @param pieces - Border and fill pieces.
+ * @returns Array of weighted ground tiles sorted by weight descending.
+ */
+export function deriveGroundTiles(pieces: readonly WildernessPiece[]): WeightedGroundTile[] {
   const counts = new Map<string, { style: number; sequence: number; count: number }>()
   const tally = (style: number, sequence: number): void => {
     const key = `${String(style)}:${String(sequence)}`
@@ -563,11 +943,37 @@ function deriveGroundTile(pieces: readonly WildernessPiece[]): { style: number;
       }
     }
   }
-  let best: { style: number; sequence: number; count: number } | null = null
+  const result = Array.from(counts.values()).map(e => ({
-  for (const entry of counts.values()) {
+    style: e.style,
-    if (best === null || entry.count > best.count) best = entry
+    sequence: e.sequence,
-  }
+    weight: e.count,
-  return best === null ? null : { style: best.style, sequence: best.sequence }
+  }))
+  result.sort((a, b) => b.weight - a.weight)
+  return result
+}
+
+/**
+ * Pick the tile the level's own pieces stand on.
+ *
+ * The shipped game picks the ground with a rarity roll over the DT1 libraries
+ * that the level type's hardcoded mask selects (`DRLGROOMTILE_GetTileCache`),
+ * and no table records which tile that lands on. The observable proxy is the
+ * pieces themselves: a border or fill DS1 is authored as a chunk of scenery
+ * sitting *on* the outdoor ground, so the floor it uses away from its own outer
+ * ring is that ground.
+ *
+ * The outer ring is excluded because that is where the cliff face and its
+ * transition tiles live. Cells with `prop1 == 0` are excluded because they are
+ * unused slots, not tiles. The most frequent survivor wins, ties going to the
+ * first seen so the choice is deterministic.
+ *
+ * @param pieces - the level's border and fill pieces.
+ * @returns the tile, or null when no piece carries any floor.
+ */
+export function deriveGroundTile(pieces: readonly WildernessPiece[]): { style: number; sequence: number } | null {
+  const tiles = deriveGroundTiles(pieces)
+  if (tiles.length === 0) return null
+  return { style: tiles[0]!.style, sequence: tiles[0]!.sequence }
 }
 
 /* ------------------------------------------------------------------------- *
@@ -628,6 +1034,7 @@ export interface WildernessStats {
   borderStamped: number
   groundCells: number
   groundTile: { style: number; sequence: number } | null
+  groundTiles?: readonly WeightedGroundTile[] | undefined
   sizeSource: string
   roadCells: number
   roadSegments: number
@@ -3261,14 +3668,49 @@ export function generateWilderness(request: WildernessRequest): WildernessResult
   const gridWidth = Math.floor(sizeX / TILES_PER_BLOCK)
   const gridHeight = Math.floor(sizeY / TILES_PER_BLOCK)
 
-  const groundTile = request.groundTile ?? CANONICAL_GROUND_TILES[request.levelTypeName] ?? deriveGroundTile(request.pieces)
+  let groundTiles: WeightedGroundTile[] | null = null
+
+  if (request.groundTiles && request.groundTiles.length > 0) {
+    groundTiles = [...request.groundTiles]
+  } else if (request.groundTile) {
+    if (isTileArray(request.groundTile)) {
+      groundTiles = [...(request.groundTile as readonly WeightedGroundTile[])]
+    } else {
+      const single = request.groundTile as { readonly style: number; readonly sequence: number }
+      groundTiles = [{ style: single.style, sequence: single.sequence, weight: 1 }]
+    }
+  } else if (request.dt1Libraries && request.dt1Libraries.length > 0) {
+    const mask = wildernessDt1Mask(request.levelTypeName)
+    const fromDt1 = deriveGroundTilesFromDt1Libraries(request.dt1Libraries, mask)
+    if (fromDt1.length > 0) groundTiles = fromDt1
+  }
+
+  if (groundTiles === null || groundTiles.length === 0) {
+    const canonicalPool = CANONICAL_GROUND_POOLS[request.levelTypeName]
+    if (canonicalPool && canonicalPool.length > 0) {
+      groundTiles = [...canonicalPool]
+    } else {
+      const canonical = CANONICAL_GROUND_TILES[request.levelTypeName]
+      if (canonical !== undefined) {
+        groundTiles = [{ style: canonical.style, sequence: canonical.sequence, weight: 1 }]
+      } else {
+        const fromPieces = deriveGroundTiles(request.pieces)
+        if (fromPieces.length > 0) groundTiles = fromPieces
+      }
+    }
+  }
+
+  const primaryGroundTile = groundTiles && groundTiles.length > 0
+    ? { style: groundTiles[0]!.style, sequence: groundTiles[0]!.sequence }
+    : null
+  const groundTile = primaryGroundTile
 
   if ((gridWidth < 3 || gridHeight < 3) && request.levelId !== 82) {
     const bridgePiece = request.pieces.find(p => p.levels.some(l => l.width >= gridWidth * TILES_PER_BLOCK && l.height >= gridHeight * TILES_PER_BLOCK)) ?? request.pieces[0]
     if (bridgePiece && bridgePiece.levels[0]) {
       const bridgeDs1 = bridgePiece.levels[0]
       const canvas = createCanvas(gridWidth * TILES_PER_BLOCK, gridHeight * TILES_PER_BLOCK, bridgeDs1.wallLayers, bridgeDs1.floorLayers, bridgeDs1.substitutionType === 1 || bridgeDs1.substitutionType === 2 ? 1 : 0)
-      if (groundTile !== null) fillGround(canvas, groundTile, 0, 0, canvas.width, canvas.height)
+      if (groundTiles !== null) fillGround(canvas, groundTiles, 0, 0, canvas.width, canvas.height, { seed: request.seed })
       stampDs1(canvas, bridgeDs1, 0, 0)
       return {
         level: {
@@ -3296,7 +3738,8 @@ export function generateWilderness(request: WildernessRequest): WildernessResult
           dt1Mask: wildernessDt1Mask(request.levelTypeName),
           subType: request.subType,
           subTheme: Math.max(0, Math.min(4, Math.floor(request.subTheme))),
-          groundTile,
+          groundTile: primaryGroundTile,
+          groundTiles: groundTiles ?? undefined,
           groundCells: canvas.width * canvas.height,
           borderPiecesAvailable: 0,
           borderBlocks: 0,
@@ -3321,7 +3764,7 @@ export function generateWilderness(request: WildernessRequest): WildernessResult
 
   const stats: WildernessStats = {
     substitutions: [], borderPieces: {}, unresolved: [], notes: [],
-    borderStamped: 0, groundCells: 0, groundTile: null, sizeSource,
+    borderStamped: 0, groundCells: 0, groundTile: null, groundTiles: undefined, sizeSource,
     roadCells: 0, roadSegments: 0, anchors: 0, specialPresets: [], entrances: [],
   }
 
@@ -3347,11 +3790,12 @@ export function generateWilderness(request: WildernessRequest): WildernessResult
   const canvas = createCanvas(gridWidth * TILES_PER_BLOCK, gridHeight * TILES_PER_BLOCK, wallLayers, floorLayers, substitutionLayers)
   const rng = new Rng(request.seed)
 
-  stats.groundTile = groundTile
+  stats.groundTile = primaryGroundTile
-  if (groundTile === null) {
+  stats.groundTiles = groundTiles ?? undefined
+  if (primaryGroundTile === null || groundTiles === null || groundTiles.length === 0) {
     throw new Error(`${where}: no piece carries a floor tile to use as ground`)
   }
-  stats.groundCells = fillGround(canvas, groundTile, 0, 0, canvas.width, canvas.height)
+  stats.groundCells = fillGround(canvas, groundTiles, 0, 0, canvas.width, canvas.height, { seed: request.seed })
 
   // Special case: Act 5 Bloody Foothills (110),
   // Act 3 Travincal (83), Act 3 Kurast Causeway (82), and Act 3 Jungles (76, 77, 78) are assembled from
@@ -3409,7 +3853,8 @@ export function generateWilderness(request: WildernessRequest): WildernessResult
         dt1Mask: wildernessDt1Mask(request.levelTypeName),
         subType: request.subType,
         subTheme: 0,
-        groundTile,
+        groundTile: primaryGroundTile,
+        groundTiles: groundTiles ?? undefined,
         groundCells: stats.groundCells,
         borderPiecesAvailable: 0,
         borderBlocks: 0,
@@ -3659,7 +4104,10 @@ export function generateWilderness(request: WildernessRequest): WildernessResult
         if (!c.floors.some(f => !f.hidden && f.prop1 !== 0)) {
           const floor = c.floors[0]
           if (floor !== undefined) {
-            Object.assign(floor, { prop1: 2, style: groundTile.style, sequence: groundTile.sequence, hidden: false })
+            const tile = groundTiles && groundTiles.length > 1
+              ? sampleGroundTile(groundTiles, x, y, { seed: request.seed })
+              : primaryGroundTile!
+            Object.assign(floor, { prop1: 2, style: tile.style, sequence: tile.sequence, hidden: false })
           }
         }
         finalGroundCells += 1
@@ -3698,7 +4146,8 @@ export function generateWilderness(request: WildernessRequest): WildernessResult
       dt1Mask: wildernessDt1Mask(request.levelTypeName),
       subType: request.subType,
       subTheme: themeIndex,
-      groundTile,
+      groundTile: primaryGroundTile,
+      groundTiles: groundTiles ?? undefined,
       groundCells: stats.groundCells,
       borderPiecesAvailable: borderPieces.length,
       borderBlocks: stats.borderStamped,

tests/wilderness-ground-blend.test.ts

@@ -0,0 +1,511 @@
+import { describe, expect, test } from "vitest"
+import {
+  fillGround,
+  sampleGroundTile,
+  deriveGroundTilesFromDt1Libraries,
+  deriveGroundTiles,
+  deriveGroundTile,
+  cellHash,
+  smoothNoise2D,
+  createCanvas,
+  generateWilderness,
+  CANONICAL_GROUND_POOLS,
+} from "../src/game/wilderness.ts"
+import type {
+  WeightedGroundTile,
+  WildernessPiece,
+} from "../src/game/wilderness.ts"
+import type { Dt1, Dt1Tile } from "../src/formats/dt1.ts"
+import type { Ds1, Ds1Cell } from "../src/formats/ds1.ts"
+
+function makeMockDs1(
+  width: number,
+  height: number,
+  floorStyle = 0,
+  floorSequence = 0,
+  customFloor?: (x: number, y: number) => { readonly style: number; readonly sequence: number } | undefined,
+): Ds1 {
+  const cells: Ds1Cell[][] = []
+  for (let y = 0; y < height; y += 1) {
+    const row: Ds1Cell[] = []
+    for (let x = 0; x < width; x += 1) {
+      const custom = customFloor?.(x, y)
+      const style = custom ? custom.style : floorStyle
+      const sequence = custom ? custom.sequence : floorSequence
+      row.push({
+        walls: [],
+        floors: [{ prop1: 2, sequence, style, unknown1: 0, unknown2: 0, hidden: false }],
+        shadows: [],
+        substitutions: [],
+      })
+    }
+    cells.push(row)
+  }
+  return {
+    version: 18,
+    width,
+    height,
+    act: 1,
+    substitutionType: 0,
+    wallLayers: 1,
+    floorLayers: 1,
+    cells,
+    objects: [],
+    npcPathOffset: null,
+  }
+}
+
+function makeMockDt1(tiles: Partial<Dt1Tile>[]): Dt1 {
+  return {
+    warnings: [],
+    versionMajor: 7,
+    versionMinor: 6,
+    tiles: tiles.map(t => ({
+      direction: 0,
+      height: -80,
+      width: 160,
+      type: t.type ?? 0,
+      style: t.style ?? 0,
+      sequence: t.sequence ?? 0,
+      materialFlags: 0,
+      roofHeight: 0,
+      rarityFrameIndex: t.rarityFrameIndex ?? 1,
+      subTileFlags: [],
+      minBlockY: 0,
+      bitmapHeight: 80,
+      blocks: [],
+      ...t,
+    })),
+  }
+}
+
+function makeTestPieces(): WildernessPiece[] {
+  return [
+    { name: "Act 1 - Wild Border 1", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 2", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 3", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 4", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 5", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 6", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 7", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 8", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 9", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 10", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 11", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+    { name: "Act 1 - Wild Border 12", border: true, levels: [makeMockDs1(8, 8, 0, 0)] },
+  ]
+}
+
+describe("Wilderness Ground Tile Blending (Issue #52)", () => {
+  describe("PRNG & Noise Primitives", () => {
+    test("cellHash produces deterministic values in [0, 1)", () => {
+      const v1 = cellHash(10, 20, 12345)
+      const v2 = cellHash(10, 20, 12345)
+      const v3 = cellHash(10, 20, 99999)
+      const v4 = cellHash(11, 20, 12345)
+
+      expect(v1).toBe(v2)
+      expect(v1).toBeGreaterThanOrEqual(0)
+      expect(v1).toBeLessThan(1)
+      expect(v1).not.toBe(v3)
+      expect(v1).not.toBe(v4)
+    })
+
+    test("smoothNoise2D produces values in [0, 1] with spatial smoothness", () => {
+      const n0 = smoothNoise2D(10, 10, 8, 42)
+      const n1 = smoothNoise2D(10.1, 10.1, 8, 42)
+      const nFar = smoothNoise2D(50, 50, 8, 42)
+
+      expect(n0).toBeGreaterThanOrEqual(0)
+      expect(n0).toBeLessThanOrEqual(1)
+      // Small step produces small difference
+      expect(Math.abs(n1 - n0)).toBeLessThan(0.1)
+      expect(nFar).toBeGreaterThanOrEqual(0)
+      expect(nFar).toBeLessThanOrEqual(1)
+    })
+  })
+
+  describe("Single-Tile Fallback (Backward Compatibility)", () => {
+    test("fillGround with a single tile object fills entire area uniformly", () => {
+      const canvas = createCanvas(20, 20, 1, 1, 0)
+      const written = fillGround(canvas, { style: 3, sequence: 7 }, 0, 0, 20, 20)
+
+      expect(written).toBe(400)
+      for (let y = 0; y < 20; y += 1) {
+        for (let x = 0; x < 20; x += 1) {
+          const floor = canvas.cells[y]![x]!.floors[0]!
+          expect(floor.style).toBe(3)
+          expect(floor.sequence).toBe(7)
+          expect(floor.hidden).toBe(false)
+        }
+      }
+    })
+
+    test("fillGround with a 1-element array fills entire area uniformly", () => {
+      const canvas = createCanvas(15, 15, 1, 1, 0)
+      const written = fillGround(canvas, [{ style: 1, sequence: 4, weight: 100 }], 0, 0, 15, 15)
+
+      expect(written).toBe(225)
+      for (let y = 0; y < 15; y += 1) {
+        for (let x = 0; x < 15; x += 1) {
+          const floor = canvas.cells[y]![x]!.floors[0]!
+          expect(floor.style).toBe(1)
+          expect(floor.sequence).toBe(4)
+        }
+      }
+    })
+
+    test("sampleGroundTile with a single tile returns it directly", () => {
+      const single = { style: 2, sequence: 5 }
+      expect(sampleGroundTile(single, 10, 10, 123)).toEqual(single)
+
+      const singleArr = [{ style: 4, sequence: 9, weight: 1 }]
+      expect(sampleGroundTile(singleArr, 10, 10, 123)).toEqual(singleArr[0])
+    })
+  })
+
+  describe("Multi-Tile Ground Blending & Weight Adherence", () => {
+    const candidates: readonly WeightedGroundTile[] = [
+      { style: 0, sequence: 0, weight: 70 },
+      { style: 0, sequence: 1, weight: 20 },
+      { style: 0, sequence: 2, weight: 10 },
+    ]
+
+    test("fillGround in spatial mode generates all candidate tiles and respects weight ratios", () => {
+      const width = 60
+      const height = 60
+      const totalCells = width * height
+      const canvas = createCanvas(width, height, 1, 1, 0)
+
+      fillGround(canvas, candidates, 0, 0, width, height, {
+        seed: 424242,
+        mode: "spatial",
+        spatialScale: 6,
+        spatialCoherence: 0.6,
+      })
+
+      const counts = new Map<number, number>()
+      for (let y = 0; y < height; y += 1) {
+        for (let x = 0; x < width; x += 1) {
+          const seq = canvas.cells[y]![x]!.floors[0]!.sequence
+          counts.set(seq, (counts.get(seq) ?? 0) + 1)
+        }
+      }
+
+      // All candidate sequences must be present
+      expect(counts.has(0)).toBe(true)
+      expect(counts.has(1)).toBe(true)
+      expect(counts.has(2)).toBe(true)
+
+      const c0 = counts.get(0)! / totalCells
+      const c1 = counts.get(1)! / totalCells
+      const c2 = counts.get(2)! / totalCells
+
+      // Expected: ~70% sequence 0, ~20% sequence 1, ~10% sequence 2
+      // Spatial noise percentile ranking guarantees global proportions very close to exact weights
+      expect(c0).toBeGreaterThanOrEqual(0.60)
+      expect(c0).toBeLessThanOrEqual(0.80)
+      expect(c1).toBeGreaterThanOrEqual(0.12)
+      expect(c1).toBeLessThanOrEqual(0.28)
+      expect(c2).toBeGreaterThanOrEqual(0.04)
+      expect(c2).toBeLessThanOrEqual(0.18)
+    })
+
+    test("fillGround in CDF mode generates all candidate tiles and respects weight ratios", () => {
+      const width = 60
+      const height = 60
+      const totalCells = width * height
+      const canvas = createCanvas(width, height, 1, 1, 0)
+
+      fillGround(canvas, candidates, 0, 0, width, height, {
+        seed: 88888,
+        mode: "cdf",
+      })
+
+      const counts = new Map<number, number>()
+      for (let y = 0; y < height; y += 1) {
+        for (let x = 0; x < width; x += 1) {
+          const seq = canvas.cells[y]![x]!.floors[0]!.sequence
+          counts.set(seq, (counts.get(seq) ?? 0) + 1)
+        }
+      }
+
+      expect(counts.has(0)).toBe(true)
+      expect(counts.has(1)).toBe(true)
+      expect(counts.has(2)).toBe(true)
+
+      const c0 = counts.get(0)! / totalCells
+      const c1 = counts.get(1)! / totalCells
+      const c2 = counts.get(2)! / totalCells
+
+      // Law of large numbers for 3600 samples: within +-8% of true probabilities
+      expect(c0).toBeGreaterThanOrEqual(0.62)
+      expect(c0).toBeLessThanOrEqual(0.78)
+      expect(c1).toBeGreaterThanOrEqual(0.14)
+      expect(c1).toBeLessThanOrEqual(0.26)
+      expect(c2).toBeGreaterThanOrEqual(0.05)
+      expect(c2).toBeLessThanOrEqual(0.16)
+    })
+
+    test("spatial mode creates contiguous natural patches (higher neighborhood correlation than random)", () => {
+      const width = 40
+      const height = 40
+      const canvasSpatial = createCanvas(width, height, 1, 1, 0)
+      const canvasCdf = createCanvas(width, height, 1, 1, 0)
+
+      fillGround(canvasSpatial, candidates, 0, 0, width, height, { seed: 100, mode: "spatial", spatialScale: 6 })
+      fillGround(canvasCdf, candidates, 0, 0, width, height, { seed: 100, mode: "cdf" })
+
+      // Count horizontal neighbor matches: how often cell(x, y) has the same sequence as cell(x+1, y)
+      let spatialMatches = 0
+      let cdfMatches = 0
+      let totalPairs = 0
+
+      for (let y = 0; y < height; y += 1) {
+        for (let x = 0; x < width - 1; x += 1) {
+          totalPairs += 1
+          if (canvasSpatial.cells[y]![x]!.floors[0]!.sequence === canvasSpatial.cells[y]![x + 1]!.floors[0]!.sequence) {
+            spatialMatches += 1
+          }
+          if (canvasCdf.cells[y]![x]!.floors[0]!.sequence === canvasCdf.cells[y]![x + 1]!.floors[0]!.sequence) {
+            cdfMatches += 1
+          }
+        }
+      }
+
+      // Spatial coherent noise should have significantly higher neighbor continuity than independent CDF noise
+      const spatialCorr = spatialMatches / totalPairs
+      const cdfCorr = cdfMatches / totalPairs
+
+      expect(spatialCorr).toBeGreaterThan(cdfCorr)
+      expect(spatialCorr).toBeGreaterThan(0.60)
+    })
+  })
+
+  describe("Deterministic PRNG Consistency", () => {
+    test("same seed produces byte-for-byte identical tile layouts", () => {
+      const candidates: readonly WeightedGroundTile[] = [
+        { style: 0, sequence: 0, weight: 60 },
+        { style: 0, sequence: 1, weight: 30 },
+        { style: 0, sequence: 2, weight: 10 },
+      ]
+
+      const canvasA = createCanvas(25, 25, 1, 1, 0)
+      const canvasB = createCanvas(25, 25, 1, 1, 0)
+
+      fillGround(canvasA, candidates, 0, 0, 25, 25, { seed: 0xfeedbeef })
+      fillGround(canvasB, candidates, 0, 0, 25, 25, { seed: 0xfeedbeef })
+
+      for (let y = 0; y < 25; y += 1) {
+        for (let x = 0; x < 25; x += 1) {
+          const floorA = canvasA.cells[y]![x]!.floors[0]!
+          const floorB = canvasB.cells[y]![x]!.floors[0]!
+          expect(floorA.style).toBe(floorB.style)
+          expect(floorA.sequence).toBe(floorB.sequence)
+        }
+      }
+    })
+
+    test("different seeds produce different ground layouts", () => {
+      const candidates: readonly WeightedGroundTile[] = [
+        { style: 0, sequence: 0, weight: 50 },
+        { style: 0, sequence: 1, weight: 50 },
+      ]
+
+      const canvasA = createCanvas(20, 20, 1, 1, 0)
+      const canvasB = createCanvas(20, 20, 1, 1, 0)
+
+      fillGround(canvasA, candidates, 0, 0, 20, 20, { seed: 111 })
+      fillGround(canvasB, candidates, 0, 0, 20, 20, { seed: 999 })
+
+      let differences = 0
+      for (let y = 0; y < 20; y += 1) {
+        for (let x = 0; x < 20; x += 1) {
+          if (canvasA.cells[y]![x]!.floors[0]!.sequence !== canvasB.cells[y]![x]!.floors[0]!.sequence) {
+            differences += 1
+          }
+        }
+      }
+
+      expect(differences).toBeGreaterThan(50)
+    })
+  })
+
+  describe("DT1 Library Derivation (deriveGroundTilesFromDt1Libraries)", () => {
+    test("filters libraries strictly according to dwDt1Mask", () => {
+      const lib0 = makeMockDt1([
+        { type: 0, style: 0, sequence: 0, rarityFrameIndex: 50 },
+      ])
+      const lib1 = makeMockDt1([
+        { type: 0, style: 0, sequence: 1, rarityFrameIndex: 20 },
+      ])
+      const lib2 = makeMockDt1([
+        { type: 0, style: 0, sequence: 2, rarityFrameIndex: 10 },
+      ])
+
+      const libraries = [lib0, lib1, lib2]
+
+      // Mask 0b001 = 1 (only lib 0)
+      const onlyLib0 = deriveGroundTilesFromDt1Libraries(libraries, 1)
+      expect(onlyLib0).toHaveLength(1)
+      expect(onlyLib0[0]).toMatchObject({ style: 0, sequence: 0, weight: 50 })
+
+      // Mask 0b101 = 5 (lib 0 and lib 2, skipping lib 1)
+      const lib0and2 = deriveGroundTilesFromDt1Libraries(libraries, 5)
+      expect(lib0and2).toHaveLength(2)
+      expect(lib0and2.map(t => t.sequence)).toEqual([0, 2])
+
+      // Mask 0b000 = 0 (no libraries active)
+      const empty = deriveGroundTilesFromDt1Libraries(libraries, 0)
+      expect(empty).toHaveLength(0)
+    })
+
+    test("filters out non-floor tiles (type !== 0) and weights by rarityFrameIndex", () => {
+      const dt1 = makeMockDt1([
+        // Floor tiles (type === 0)
+        { type: 0, style: 1, sequence: 0, rarityFrameIndex: 60 },
+        { type: 0, style: 1, sequence: 1, rarityFrameIndex: 40 },
+        // Same style/seq variant in library: weights should accumulate
+        { type: 0, style: 1, sequence: 1, rarityFrameIndex: 10 },
+        // Wall tile (type === 1) - must be excluded
+        { type: 1, style: 1, sequence: 0, rarityFrameIndex: 99 },
+        // Roof tile (type === 2) - must be excluded
+        { type: 2, style: 1, sequence: 0, rarityFrameIndex: 99 },
+      ])
+
+      const result = deriveGroundTilesFromDt1Libraries([dt1], 1)
+      expect(result).toHaveLength(2)
+
+      // Expected ordering: highest weight first
+      // seq 0 has 60, seq 1 has 40 + 10 = 50
+      expect(result[0]).toMatchObject({ style: 1, sequence: 0, weight: 60 })
+      expect(result[1]).toMatchObject({ style: 1, sequence: 1, weight: 50 })
+    })
+
+    test("handles empty libraries or libraries with no floor tiles gracefully", () => {
+      expect(deriveGroundTilesFromDt1Libraries([], 0xff)).toEqual([])
+
+      const noFloors = makeMockDt1([{ type: 1, style: 0, sequence: 0 }])
+      expect(deriveGroundTilesFromDt1Libraries([noFloors], 1)).toEqual([])
+    })
+  })
+
+  describe("Piece Floor Derivation (deriveGroundTiles & deriveGroundTile)", () => {
+    test("derives candidate ground tiles with frequencies from interior floor cells", () => {
+      // Create a piece with interior floor tiles:
+      // 8x8 piece has interior from x=1..6, y=1..6 (36 interior cells)
+      // Set cells x=2..4, y=2..4 to sequence 1 (9 cells)
+      const level = makeMockDs1(8, 8, 0, 0, (x, y) => {
+        if (x >= 2 && x <= 4 && y >= 2 && y <= 4) {
+          return { style: 0, sequence: 1 }
+        }
+        return undefined
+      })
+
+      const pieces: WildernessPiece[] = [{ name: "Test Piece", border: true, levels: [level] }]
+      const tiles = deriveGroundTiles(pieces)
+
+      expect(tiles.length).toBe(2)
+      // Sequence 0 is the majority, sequence 1 has 9 cells
+      expect(tiles[0]!.sequence).toBe(0)
+      expect(tiles[1]!.sequence).toBe(1)
+      expect(tiles[1]!.weight).toBe(9)
+
+      // deriveGroundTile should return the most frequent interior tile
+      const primary = deriveGroundTile(pieces)
+      expect(primary).toEqual({ style: 0, sequence: 0 })
+    })
+  })
+
+  describe("generateWilderness Integration", () => {
+    test("generates wilderness with explicit groundTiles blend", () => {
+      const pieces = makeTestPieces()
+      const candidateTiles: readonly WeightedGroundTile[] = [
+        { style: 0, sequence: 0, weight: 70 },
+        { style: 0, sequence: 1, weight: 30 },
+      ]
+
+      const result = generateWilderness({
+        levelId: 2,
+        levelName: "Blood Moor Blend Test",
+        levelTypeName: "Act 1 - Wilderness",
+        sizeX: 80,
+        sizeY: 80,
+        subType: 6,
+        subTheme: 0,
+        seed: 123456,
+        pieces,
+        substitutions: [],
+        groundTiles: candidateTiles,
+      })
+
+      expect(result.stats.groundTiles).toBeDefined()
+      const statsTiles = result.stats.groundTiles as readonly WeightedGroundTile[]
+      expect(statsTiles).toHaveLength(2)
+
+      // Verify level cells contain both sequences
+      let seq0Count = 0
+      let seq1Count = 0
+      for (let y = 0; y < result.level.height; y += 1) {
+        for (let x = 0; x < result.level.width; x += 1) {
+          const floor = result.level.cells[y]![x]!.floors[0]
+          if (floor && !floor.hidden) {
+            if (floor.sequence === 0) seq0Count += 1
+            if (floor.sequence === 1) seq1Count += 1
+          }
+        }
+      }
+
+      expect(seq0Count).toBeGreaterThan(0)
+      expect(seq1Count).toBeGreaterThan(0)
+      expect(seq0Count).toBeGreaterThan(seq1Count)
+    })
+
+    test("generates wilderness with single groundTile maintaining pure single-tile fallback", () => {
+      const pieces = makeTestPieces()
+      const result = generateWilderness({
+        levelId: 2,
+        levelName: "Blood Moor Single Tile",
+        levelTypeName: "Act 1 - Wilderness",
+        sizeX: 80,
+        sizeY: 80,
+        subType: 6,
+        subTheme: 0,
+        seed: 654321,
+        pieces,
+        substitutions: [],
+        groundTile: { style: 0, sequence: 0 },
+      })
+
+      expect(result.stats.groundTile).toEqual({ style: 0, sequence: 0 })
+    })
+
+    test("generates wilderness with dt1Libraries deriving ground tiles automatically", () => {
+      const pieces = makeTestPieces()
+      const dt1 = makeMockDt1([
+        { type: 0, style: 0, sequence: 0, rarityFrameIndex: 80 },
+        { type: 0, style: 0, sequence: 1, rarityFrameIndex: 20 },
+      ])
+
+      const result = generateWilderness({
+        levelId: 2,
+        levelName: "Blood Moor DT1 Test",
+        levelTypeName: "Act 1 - Wilderness",
+        sizeX: 80,
+        sizeY: 80,
+        subType: 6,
+        subTheme: 0,
+        seed: 777777,
+        pieces,
+        substitutions: [],
+        dt1Libraries: [dt1],
+      })
+
+      expect(result.stats.groundTiles).toBeDefined()
+      const statsTiles = result.stats.groundTiles as readonly WeightedGroundTile[]
+      expect(statsTiles).toHaveLength(2)
+      expect(statsTiles[0]!.sequence).toBe(0)
+      expect(statsTiles[1]!.sequence).toBe(1)
+    })
+  })
+})