feat: trees

AGENTS.md

@@ -56,7 +56,9 @@ rules live in `.agents/rules/*.md`.
     `Mesh` (indexed tris), `Sprite` (Y-axis billboard), `Terrain` (procedural
     heightfield around the room: flat clearing in the center, rolling hills, tall
     edge peaks. `Terrain.ground` builds the outdoor mesh with a hole for the room;
-    `Terrain.height` is the shared ground-height sampler for the player).
+    `Terrain.height` is the shared ground-height sampler for the player), `Tree`
+    (procedural low-poly oak/spruce geometry, sapling..full via a `growth` knob;
+    `Tree.build` appends into shared trunk + foliage meshes).
 - `app/` — browser glue.
   - `main.ts` — game loop, input, preset switching, canvas blit, FPS meter.
   - `assets.ts` — load `/assets/*.png` → `Texture` (zero-copy; ImageData bytes
@@ -64,8 +66,10 @@ rules live in `.agents/rules/*.md`.
   - `level.ts` — builds the playground: a flat stone-floored room (three thick
     walls via `slab`, north side open) in the center of a big grassy `Terrain`
     world (~20x across).
-    Per-texture meshes incl. the outdoor grass `ground`, `Aabb` colliders, NPC
-    position, `Terrain` config + `GROUND_DIVISIONS`/`GROUND_UV`, sky/cloud config.
+    Per-texture meshes incl. the outdoor grass `ground` and a scattered forest
+    (`scatterTrees` → `trunks`/`oakFoliage`/`spruceFoliage`, `TREE_COUNT`/`_SEED`/
+    `_REACH`), `Aabb` colliders (incl. grown-tree trunks), NPC position, `Terrain`
+    config + `GROUND_DIVISIONS`/`GROUND_UV`, sky/cloud config.
     The stone floor is lifted by `FLOOR_LIFT` (a z-bias) so it stays clean over the
     terrain skirt that laps under the room edges. Room surfaces are single flat
     quads -- no subdivision needed since texturing is perspective-correct; ground
@@ -79,8 +83,9 @@ rules live in `.agents/rules/*.md`.
   `#fps` meter div (styled inline).
 - `scripts/gen-assets.ts` — procedurally draws the placeholder textures and
   writes PNGs (hand-rolled encoder via `node:zlib`). Run via `bun run assets`.
-- `assets/` — generated `floor/grass/wall/crate/npc` PNGs (`floor` = room stone,
-  `grass` = outdoor ground). Swap for real art anytime;
+- `assets/` — generated `floor/grass/bark/leaf/needle/wall/crate/npc` PNGs
+  (`floor` = room stone, `grass` = outdoor ground, `bark`/`leaf`/`needle` = tree
+  trunk/oak/spruce). Swap for real art anytime;
   filenames are the contract.
 - `server/` — Bun server stub. `shared/` — isomorphic slot.
 
@@ -88,7 +93,8 @@ rules live in `.agents/rules/*.md`.
 
 `Player.update` → build `Camera` → `Camera.viewProjection` →
 `Sky.render` (fills color + resets depth, replaces a clear) →
-`Rasterizer.draw` ground, floor, walls, crate (one call per texture) →
+`Rasterizer.draw` ground, floor, walls, crate, tree trunks, oak foliage, spruce
+foliage (one call per texture) →
 `Sprite.billboard(npc)` drawn via `Rasterizer.draw` →
 `Framebuffer.quantize` → `present` (integer-scale, letterboxed blit;
 `imageSmoothingEnabled` follows `upscaleFilter`).
@@ -131,6 +137,21 @@ Both are exported presets in `app/level.ts`; the active one is set in
 branching in the cloud shader. Cost scales with sky resolution — fine at
 `standard`, heavy at `clean` (mitigate: fewer fbm octaves or half-res sky).
 
+## Trees (`engine/scene/Tree.ts`)
+
+Procedural low-poly geometry, faceted flat-shaded like everything else. Two
+`kind`s carry the species read purely by silhouette:
+- **`oak`** — short tapered trunk, a couple of branches, a broad cluster of
+  lumpy canopy `blob`s (wider than tall, bushy).
+- **`spruce`** — tall thin trunk under stacked narrowing `cone` tiers pointing
+  to a tip (taller than wide, conical).
+
+`growth` (0..1) runs **sapling → full grown**: it scales height/girth and adds
+canopy blobs (oak) / tiers (spruce); `seed` gives each tree its own wobble.
+`Tree.build` appends into caller meshes so a forest batches into 3 draw calls
+(one bark trunk mesh, oak-leaf and spruce-needle foliage meshes). `app/level.ts`
+`scatterTrees` seeds the forest; add a species by extending the union + a builder.
+
 ## Controls
 
 WASD move · **Shift** run (speed ×`RUN_MULTIPLIER` in `app/player.ts`) · mouse