feat(desktop): LV_ASSET_PACK=cc0 素材渲染路径

VillageArt 支持 CC0 素材包切换（环境变量 LV_ASSET_PACK=cc0）：Kenney 地块替代草地（棋盘双绿）/石径纹理，Puny 角色图集（与江南人物同 cell 几何）替换五变体角色；水面/屋檐/桥/灯笼/竹丛等江南图块保留并存于同一场景，江南图集仍作为水与建筑纹理源；未设环境变量时行为与既有路径一致（全部既有测试不变）。

1 files changed, 41 insertions, 9 deletions

diff --git a/src/LivingVillage.Desktop/VillageArt.fs b/src/LivingVillage.Desktop/VillageArt.fs
index 6f5af07..efed4ee 100644
--- a/src/LivingVillage.Desktop/VillageArt.fs
+++ b/src/LivingVillage.Desktop/VillageArt.fs
@@ -1,5 +1,6 @@
 namespace LivingVillage.Desktop
 
+open System
 open Microsoft.Xna.Framework.Graphics
 open LivingVillage.Kernel
 open LivingVillage.Kernel.Sim
@@ -95,7 +96,8 @@ module VillageArt =
     type ArtTextures =
         { TileAtlas: Texture2D
           CharacterAtlas: Texture2D
-          InteriorAtlas: Texture2D }
+          InteriorAtlas: Texture2D
+          Cc0TileAtlas: Texture2D option }
 
     type private TileSprite =
         | GrassSprite
@@ -122,6 +124,16 @@ module VillageArt =
 
     type private XnaColor = Microsoft.Xna.Framework.Color
     type private XnaRectangle = Microsoft.Xna.Framework.Rectangle
+
+    /// CC0 pack ground tiles: 0 grass bright / 1 grass deep (checker) / 2 path / 3 dirt.
+    let private cc0GroundRect (position: TilePosition) : XnaRectangle =
+        let index = if (position.X + position.Y) % 2 = 1 then 1 else 0
+        XnaRectangle(index * Sim.tilePixels, 0, Sim.tilePixels, Sim.tilePixels)
+
+    let private cc0PathRect : XnaRectangle = XnaRectangle(2 * Sim.tilePixels, 0, Sim.tilePixels, Sim.tilePixels)
+
+    let private drawCc0Tile (spriteBatch: SpriteBatch) (cc0: Texture2D) (tint: XnaColor) (source: XnaRectangle) (screenX: int) (screenY: int) =
+        spriteBatch.Draw(cc0, XnaRectangle(screenX, screenY, Sim.tilePixels, Sim.tilePixels), Nullable(source), tint)
     type private XnaVector2 = Microsoft.Xna.Framework.Vector2
 
     let private position x y : TilePosition =
@@ -347,10 +359,24 @@ module VillageArt =
         else
             texture
 
+    let useCc0Pack () : bool =
+        System.Environment.GetEnvironmentVariable("LV_ASSET_PACK") = "cc0"
+
+    let cc0TileAtlasRelativePath = "Assets/cc0-tiles.png"
+    let cc0TileAtlasWidth = Sim.tilePixels * 4
+    let cc0CharacterAtlasRelativePath = "Assets/cc0-characters.png"
+
     let loadTextures (device: GraphicsDevice) : ArtTextures =
+        let cc0 =
+            if useCc0Pack () then
+                Some(loadTexture device cc0TileAtlasRelativePath cc0TileAtlasWidth Sim.tilePixels)
+            else
+                None
+        let characterPath = if useCc0Pack () then cc0CharacterAtlasRelativePath else characterAtlasRelativePath
         { TileAtlas = loadTexture device worldAtlasRelativePath worldAtlasWidth worldAtlasHeight
-          CharacterAtlas = loadTexture device characterAtlasRelativePath characterAtlasWidth characterAtlasHeight
-          InteriorAtlas = loadTexture device interiorAtlasRelativePath interiorAtlasWidth interiorAtlasHeight }
+          CharacterAtlas = loadTexture device characterPath characterAtlasWidth characterAtlasHeight
+          InteriorAtlas = loadTexture device interiorAtlasRelativePath interiorAtlasWidth interiorAtlasHeight
+          Cc0TileAtlas = cc0 }
 
     let atlasTileRectangle (index: int) : Microsoft.Xna.Framework.Rectangle =
         XnaRectangle(index * Sim.tilePixels, 0, Sim.tilePixels, Sim.tilePixels)
@@ -422,21 +448,27 @@ module VillageArt =
             drawWorldTile spriteBatch textures camera viewportWidth viewportHeight position sprite tint
         let rippleFrame = waterFrameTick tick
 
+        let drawBaseTile (position: TilePosition) =
+            match textures.Cc0TileAtlas with
+            | Some cc0 -> drawCc0Tile spriteBatch cc0 tint (cc0GroundRect position) (position.X * Sim.tilePixels - int camera.X) (position.Y * Sim.tilePixels - int camera.Y)
+            | None -> draw position GrassSprite
+
         let tx0 = max 0 (int camera.X / Sim.tilePixels)
         let ty0 = max 0 (int camera.Y / Sim.tilePixels)
         let tx1 = min (Sim.mapWidthTiles - 1) ((int camera.X + viewportWidth) / Sim.tilePixels + 1)
         let ty1 = min (Sim.mapHeightTiles - 1) ((int camera.Y + viewportHeight) / Sim.tilePixels + 1)
         for y in ty0 .. ty1 do
             for x in tx0 .. tx1 do
-                draw (tilePosition x y) GrassSprite
+                drawBaseTile (tilePosition x y)
 
         for localPosition, kind in plan.Grounds do
             let position = worldTile plan localPosition
-            let sprite =
-                match kind with
-                | Water -> if rippleFrame = 0 then WaterSprite else WaterSpriteB
-                | StonePath -> StonePathSprite
-            draw position sprite
+            match kind with
+            | Water -> draw position (if rippleFrame = 0 then WaterSprite else WaterSpriteB)
+            | StonePath ->
+                match textures.Cc0TileAtlas with
+                | Some cc0 -> drawCc0Tile spriteBatch cc0 tint cc0PathRect (position.X * Sim.tilePixels - int camera.X) (position.Y * Sim.tilePixels - int camera.Y)
+                | None -> draw position StonePathSprite
 
         let drawHouse doorTile =
             let position = worldTile plan doorTile