feat(desktop): P26 民居立面第二变体（挑檐/木格栅窗/院门）沿河沿路交替

3 files changed, 60 insertions, 16 deletions

diff --git a/src/LivingVillage.Desktop.Tests/PrototypeTests.fs b/src/LivingVillage.Desktop.Tests/PrototypeTests.fs
index e58139c..a38228f 100644
--- a/src/LivingVillage.Desktop.Tests/PrototypeTests.fs
+++ b/src/LivingVillage.Desktop.Tests/PrototypeTests.fs
@@ -1104,6 +1104,23 @@ type PrototypeTests () =
         // 953775FA 硬对齐由 --performance-baseline 于 finalWorld 支线证据。
 
     [<TestMethod>]
+    member _.HouseFacadeVariantsAlternateAlongTheVillage () =
+        // P26：512 大图上两种民居立面都要出现，且按位置确定性交替（纯函数）。
+        let map = MapGen.generateWithSize 512 384 (uint64 4242)
+        let variants = map.Buildings |> List.map VillageArt.houseFacadeVariant
+        Assert.IsTrue(Set.ofList variants |> Set.contains 0, "variant A must appear")
+        Assert.IsTrue(Set.ofList variants |> Set.contains 1, "variant B must appear")
+        let repeated = MapGen.generateWithSize 512 384 (uint64 4242)
+        Assert.AreEqual<(int list)>(variants, repeated.Buildings |> List.map VillageArt.houseFacadeVariant)
+        // Neighbouring buildings along the same river bank must flip variant, i.e. not one solid run.
+        let flipped =
+            variants
+            |> List.pairwise
+            |> List.filter (fun (a, b) -> a <> b)
+            |> List.length
+        Assert.IsTrue(flipped > 0, "facades must alternate, not stay one variant")
+
+    [<TestMethod>]
     member _.JiangnanArtAssetsArePackagedAsRealPngFiles () =
         let requiredAssets =
             [ "Assets/jiangnan-world.png"
@@ -1116,9 +1133,10 @@ type PrototypeTests () =
 
         Assert.AreEqual<string list>([], missing, sprintf "Missing Jiangnan PNG assets: %s" (String.concat ", " missing))
 
-        // The baked world atlas must match the 28-slot layout the renderer indexes into
-        // (P17 added 石灯笼/水缸/摊贩摊位 as slots 25..27).
-        Assert.AreEqual<int>(28, VillageArt.worldTileCount)
+        // The baked world atlas must match the 31-slot layout the renderer indexes into
+        // (P17 added 石灯笼/水缸/摊贩摊位 as slots 25..27; P26 added the variant-B house
+        // parts 屋檐挑出/木格栅窗/院门 as slots 28..30).
+        Assert.AreEqual<int>(31, VillageArt.worldTileCount)
         let worldPath = Path.Combine(AppContext.BaseDirectory, "Assets/jiangnan-world.png")
         let header = File.ReadAllBytes worldPath
         let be32 offset =
@@ -1128,7 +1146,7 @@ type PrototypeTests () =
             ||| int header.[offset + 3]
         let atlasWidth : int = be32 16
         let atlasHeight : int = be32 20
-        Assert.IsTrue((atlasWidth = VillageArt.worldAtlasWidth), "world atlas width must match 28 x 32px slots")
+        Assert.IsTrue((atlasWidth = VillageArt.worldAtlasWidth), "world atlas width must match 31 x 32px slots")
         Assert.IsTrue((atlasHeight = VillageArt.worldAtlasHeight), "world atlas height must stay 32px")
 
     [<TestMethod>]
diff --git a/src/LivingVillage.Desktop/Assets/jiangnan-world.png b/src/LivingVillage.Desktop/Assets/jiangnan-world.png
index 6e97728..ea2866d 100644
--- a/src/LivingVillage.Desktop/Assets/jiangnan-world.png
+++ b/src/LivingVillage.Desktop/Assets/jiangnan-world.png
diff --git a/src/LivingVillage.Desktop/VillageArt.fs b/src/LivingVillage.Desktop/VillageArt.fs
index 12c17ba..f303620 100644
--- a/src/LivingVillage.Desktop/VillageArt.fs
+++ b/src/LivingVillage.Desktop/VillageArt.fs
@@ -154,6 +154,9 @@ module VillageArt =
         | StoneLanternSprite
         | WaterVatSprite
         | StallSprite
+        | RoofEaveOverhangSprite
+        | WallLatticeSprite
+        | CourtyardDoorSprite
 
     type private XnaColor = Microsoft.Xna.Framework.Color
     type private XnaRectangle = Microsoft.Xna.Framework.Rectangle
@@ -496,7 +499,7 @@ module VillageArt =
     let characterAtlasRelativePath = "Assets/jiangnan-characters.png"
     let interiorAtlasRelativePath = "Assets/jiangnan-interior.png"
 
-    let worldTileCount = 28
+    let worldTileCount = 31
     let worldAtlasWidth = Sim.tilePixels * worldTileCount
     let worldAtlasHeight = Sim.tilePixels
     let characterAtlasWidth = 32 * 5 * 4 * 6
@@ -570,6 +573,9 @@ module VillageArt =
             | StoneLanternSprite -> 25
             | WaterVatSprite -> 26
             | StallSprite -> 27
+            | RoofEaveOverhangSprite -> 28
+            | WallLatticeSprite -> 29
+            | CourtyardDoorSprite -> 30
         XnaRectangle(index * Sim.tilePixels, 0, Sim.tilePixels, Sim.tilePixels)
 
     let private tilePosition x y : TilePosition =
@@ -603,6 +609,13 @@ module VillageArt =
     let private fillRect (spriteBatch: SpriteBatch) (pixel: Texture2D) (color: XnaColor) (x: int) (y: int) (w: int) (h: int) =
         spriteBatch.Draw(pixel, XnaRectangle(x, y, max 1 w, max 1 h), color)
 
+    /// P26 民居立面变体：按位置确定性交替两种立面（沿河沿路分布）。
+    /// 0 = 黛瓦脊 + 木墙/窗 + 门（P24 原样）；1 = 挑檐挑出 + 木格栅窗 + 院门。
+    /// 纯函数、不改变任何瓦片/可达性语义；64x48 与 256x192 的 tiles checksum 不受影响。
+    let houseFacadeVariant (building: MapGen.Building) : int =
+        let remainder = (building.Left + building.Top) % 2
+        if remainder < 0 then remainder + 2 else remainder
+
     /// 生成器世界里的桥面与沿河民居（白墙黑瓦色块 + 门）；坐标由调用方按相机换算。
     let private drawMapStructures
         (spriteBatch: SpriteBatch)
@@ -618,18 +631,31 @@ module VillageArt =
         for building in map.Buildings do
             let left = building.Left
             let right = building.Left + building.Width - 1
-            // P24：改用 256x192 同款民宅部件——黛瓦（脊/檐）+ 木墙/窗 + 门。
-            for row in building.Top .. building.DoorY - 1 do
-                let roofSprite = if row = building.Top then RoofRidgeSprite else RoofEaveSprite
-                let source = tileSourceRectangle roofSprite
+            let drawCell sprite x y =
+                spriteBatch.Draw(textures.TileAtlas, XnaRectangle(tileX x, tileY y, cell, cell), tileSourceRectangle sprite, XnaColor.White)
+            match houseFacadeVariant building with
+            | 0 ->
+                // 变体 A（P24）：黛瓦（脊/檐）+ 木墙/窗 + 门。
+                for row in building.Top .. building.DoorY - 1 do
+                    let roofSprite = if row = building.Top then RoofRidgeSprite else RoofEaveSprite
+                    for x in left .. right do
+                        drawCell roofSprite x row
+                for x in left .. right do
+                    let wallSprite =
+                        if x = building.DoorX then DoorSprite
+                        elif (x - left) % 2 = 0 then WallWindowSprite
+                        else WallWoodSprite
+                    drawCell wallSprite x building.DoorY
+            | _ ->
+                // 变体 B（P26）：挑檐向两侧各出一格 + 木格栅窗 + 院门。
+                for x in (left - 1) .. (right + 1) do
+                    drawCell RoofEaveOverhangSprite x building.Top
                 for x in left .. right do
-                    spriteBatch.Draw(textures.TileAtlas, XnaRectangle(tileX x, tileY row, cell, cell), source, XnaColor.White)
-            for x in left .. right do
-                let wallSprite =
-                    if x = building.DoorX then DoorSprite
-                    elif (x - left) % 2 = 0 then WallWindowSprite
-                    else WallWoodSprite
-                spriteBatch.Draw(textures.TileAtlas, XnaRectangle(tileX x, tileY building.DoorY, cell, cell), tileSourceRectangle wallSprite, XnaColor.White)
+                    let wallSprite =
+                        if x = building.DoorX then CourtyardDoorSprite
+                        elif (x - left) % 2 = 0 then WallLatticeSprite
+                        else WallWoodSprite
+                    drawCell wallSprite x building.DoorY
 
     /// 桥头灯笼瓦片：每座桥每列的最上/最下一格（桥两端），用于挂灯笼与夜间暖光。
     let bridgeLanternTiles (map: MapGen.Result) : (int * int) list =