feat(mapgen): P28 512 沿河民居加密至 16 并宽度 2/3/4 分层

- ExtraRiversideHouses 10 -> 16（沿河 +6 座），宽度加权 2/3/4 形成聚落层次
- 仅 large 分支执行、默认图不消耗 RNG：64x48=6042052、256x192=1284656962 锁定不变
- 新增 LargeMapHouseDensityHierarchyOnlyGrowsLargeMaps 回归

1 files changed, 14 insertions, 9 deletions

diff --git a/src/LivingVillage.Desktop/MapGen.fs b/src/LivingVillage.Desktop/MapGen.fs
index ce9fb3a..3705635 100644
--- a/src/LivingVillage.Desktop/MapGen.fs
+++ b/src/LivingVillage.Desktop/MapGen.fs
@@ -97,6 +97,7 @@ module MapGen =
     /// P23 尺寸自适应参数：河道数量随高度增长（约每 96 行一条），其余沿用默认。
     /// 64x48 / 256x192 仍得到 2 条河道，与既有输出逐字节一致；512x384 得到 4 条。
     /// P24：仅对大于 256x192 的图追加沿河民居（泊松散布），保证既有 checksum 不变。
+    /// P28：大图沿河民居由 10 增至 16（+6 座，宽度 2/3/4 变化），默认图仍为 0、不消耗 RNG。
     let paramsForSize (width: int) (height: int) (seed: uint64) : Params =
         let base_ = defaultParams seed
         let large = width > 256 || height > 192
@@ -104,7 +105,7 @@ module MapGen =
             Width = width
             Height = height
             RiverCount = max base_.RiverCount (max 1 (height / 96))
-            ExtraRiversideHouses = (if large then 10 else 0)
+            ExtraRiversideHouses = (if large then 16 else 0)
             DecorativeStones = not large
             RiverDecorations = large }
 
@@ -307,18 +308,20 @@ module MapGen =
         // 5b) P24：大图沿河民居加密。从既有路网瓦片出发，向四邻定向落位 3x2 白墙黛瓦民居，
         //     门开向相邻路格并接入路网（BFS 可达）；仅在 ExtraRiversideHouses>0 时执行，
         //     且只在核心区外的草地落位，故 64x48/256x192 输出逐字节不变。
+        //     P28：宽度按 2/3/4 加权变化（2=附属小筑、4=大宅），形成聚落层次而非等距重复；
+        //     数量 10 -> 16（沿河再增 6 座）。仍只在大图分支执行，默认图 RNG 不消耗，checksum 不变。
         if p.ExtraRiversideHouses > 0 then
-            let footprintFree (left: int) (top: int) =
-                left >= 1 && left + 2 <= w - 2 && top >= 1 && top + 1 <= h - 2
-                && [ for dx in 0 .. 2 do
+            let footprintFree (left: int) (top: int) (width: int) =
+                left >= 1 && left + width - 1 <= w - 2 && top >= 1 && top + 1 <= h - 2
+                && [ for dx in 0 .. width - 1 do
                        for dy in 0 .. 1 -> (left + dx, top + dy) ]
                    |> List.forall (fun (x, y) ->
                        tiles.[idx x y] = int GroundTile.Grass
                        && not (inCore x y))
-            let overlaps (left: int) (top: int) =
+            let overlaps (left: int) (top: int) (width: int) =
                 buildings
                 |> List.exists (fun b ->
-                    left < b.Left + b.Width && b.Left < left + 3
+                    left < b.Left + b.Width && b.Left < left + width
                     && top < b.Top + b.Height && b.Top < top + 2)
             let directions = [ (0, -1); (0, 1); (-1, 0); (1, 0) ]
             let mutable extraPlaced = 0
@@ -331,15 +334,17 @@ module MapGen =
                 if paths.Length > 0 then
                     let pathX, pathY = List.item (int (raw % uint64 paths.Length)) paths
                     let dirX, dirY = directions.[int ((raw >>> 32) % 4UL)]
+                    let widthRoll = int ((raw >>> 40) % 10UL)
+                    let buildingWidth = if widthRoll < 5 then 3 elif widthRoll < 8 then 2 else 4
                     let doorX = pathX + dirX
                     let doorY = pathY + dirY
-                    let left = doorX - 1
+                    let left = doorX - buildingWidth / 2
                     let top = doorY - 1
-                    if footprintFree left top && not (overlaps left top) then
+                    if footprintFree left top buildingWidth && not (overlaps left top buildingWidth) then
                         let building =
                             { Left = left
                               Top = top
-                              Width = 3
+                              Width = buildingWidth
                               Height = 2
                               DoorX = doorX
                               DoorY = doorY }