feat: birch

AGENTS.md

@@ -72,7 +72,7 @@ rules live in `.agents/rules/*.md`.
     edge peaks. `Terrain.patch` builds one ground patch over a rectangle -- called
     per chunk, aligned so patches weld crack-free, with a hole for the room;
     `Terrain.height` is the shared ground-height sampler for the player), `Tree`
-    (procedural low-poly oak/spruce geometry, sapling..full via a `growth` knob;
+    (procedural low-poly oak/spruce/birch geometry, sapling..full via a `growth` knob;
     `Tree.build` appends into shared trunk + foliage meshes), `Boulder`
     (procedural low-poly rock: a squashed, jittered, part-buried sphere;
     `Boulder.build` appends into a shared mesh), `Bush` (cluster of small leaf
@@ -116,7 +116,7 @@ rules live in `.agents/rules/*.md`.
     scattered (`placeMobs`; `FROG_/BEE_COUNT`, `MOB_SEED`, `MOB_REACH` — mobs move,
     so they carry no baked colliders), then `buildChunks` bakes
     terrain + props into a `CHUNK_GRID` x `CHUNK_GRID` grid of `Chunk`s (each =
-    per-texture meshes grass/bark/leaf/needle/rock/flowers + a tight AABB) that
+    per-texture meshes grass/bark/birchBark/leaf/needle/rock/flowers + a tight AABB) that
     `main` frustum-culls; bushes fold into the leaf mesh, flowers get their own
     (drawn double-sided). Trees + boulders are baked **twice** — full geometry and
     a low-poly impostor (`barkFar/leafFar/needleFar/rockFar`, via the builders'
@@ -134,9 +134,9 @@ 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/bark/leaf/needle/rock/flower/wall/crate/npc/frog/bee`
-  PNGs (`floor` = room stone, `grass` = outdoor ground, `bark`/`leaf`/`needle` =
-  tree trunk/oak/spruce, `rock` = boulders, `flower` = 2x2 bloom-color atlas,
+- `assets/` — generated `floor/grass/bark/birch/leaf/needle/rock/flower/wall/crate/npc/frog/bee`
+  PNGs (`floor` = room stone, `grass` = outdoor ground, `bark`/`birch`/`leaf`/`needle` =
+  brown trunk / white birch trunk / oak leaf / spruce needle, `rock` = boulders, `flower` = 2x2 bloom-color atlas,
   `frog`/`bee` = mob skin atlases: frog green + eye tone; bee stripe bands +
   head-dark + wing-pale regions).
   Swap for real art anytime;
@@ -271,18 +271,24 @@ branching in the cloud shader. Cost scales with sky resolution — fine at
 
 ## Trees (`engine/scene/Tree.ts`)
 
-Procedural low-poly geometry, faceted flat-shaded like everything else. Two
+Procedural low-poly geometry, faceted flat-shaded like everything else. Three
 `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).
+- **`birch`** — silver birch: tall, slender, near-straight trunk with an airy,
+  high, slightly drooping canopy (lean silhouette). Uses a separate **white**
+  `birch` bark texture (brown bark can't stand in), and shares the oak `leaf`
+  foliage.
 
 `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.
+canopy blobs (oak/birch) / tiers (spruce); `seed` gives each tree its own wobble.
+`Tree.build` appends into caller-chosen trunk + foliage meshes, so a forest still
+batches into a few draw calls (brown-bark trunks, white-birch trunks, oak/birch
+leaf foliage, spruce needles). `app/level.ts` `placeTrees` seeds the forest and
+rolls the species; add one by extending the union + a builder (a new bark/leaf
+look also needs its own texture + per-chunk mesh channel — see `birchBark`).
 
 **Boulders** (`engine/scene/Boulder.ts`) work the same way: `Boulder.build`
 appends a squashed, per-vertex-jittered low-poly sphere (seam/pole-safe so it

CLAUDE.md

@@ -5,3 +5,6 @@
 @.agents/rules/forge-sync.md
 @.agents/rules/openspec.md
 @.agents/rules/quality.md
+
+Don't nudge the user towards branching or commiting. User is perfectly capable of handling this.
+

README.md

@@ -5,3 +5,7 @@
   - all the knobs
 
 
+Start to make cohesive game:
+
+- Split apart the "engine" and "game"
+

app/assets.ts

@@ -1,6 +1,7 @@
 import type { Texture } from "../engine/render/Texture"
 import barkUrl from "../assets/bark.png"
 import beeUrl from "../assets/bee.png"
+import birchUrl from "../assets/birch.png"
 import crateUrl from "../assets/crate.png"
 import floorUrl from "../assets/floor.png"
 import flowerUrl from "../assets/flower.png"
@@ -16,6 +17,7 @@ export type Textures = {
   floor: Texture
   grass: Texture
   bark: Texture
+  birch: Texture
   leaf: Texture
   needle: Texture
   rock: Texture
@@ -29,10 +31,11 @@ export type Textures = {
 
 /** Load every game texture up front. Call once before starting the loop. */
 export async function loadTextures(): Promise<Textures> {
-  const [floor, grass, bark, leaf, needle, rock, flower, wall, crate, npc, frog, bee] = await Promise.all([
+  const [floor, grass, bark, birch, leaf, needle, rock, flower, wall, crate, npc, frog, bee] = await Promise.all([
     loadTexture(floorUrl),
     loadTexture(grassUrl),
     loadTexture(barkUrl),
+    loadTexture(birchUrl),
     loadTexture(leafUrl),
     loadTexture(needleUrl),
     loadTexture(rockUrl),
@@ -43,7 +46,7 @@ export async function loadTextures(): Promise<Textures> {
     loadTexture(frogUrl),
     loadTexture(beeUrl),
   ])
-  return { floor, grass, bark, leaf, needle, rock, flower, wall, crate, npc, frog, bee }
+  return { floor, grass, bark, birch, leaf, needle, rock, flower, wall, crate, npc, frog, bee }
 }
 
 function loadTexture(url: string): Promise<Texture> {

app/level.ts

@@ -35,6 +35,9 @@ export type Chunk = {
   maxZ: number
   grass: Mesh
   bark: Mesh
+  /** Birch trunks (white bark texture) -- separate mesh since a draw is one mesh +
+   *  one texture, and silver birch bark can't share the brown oak/spruce bark. */
+  birchBark: Mesh
   leaf: Mesh
   needle: Mesh
   rock: Mesh
@@ -42,8 +45,9 @@ export type Chunk = {
   flowers: Mesh
   /** Cheap low-poly impostors of the same trees/boulders, drawn instead of the
    *  full meshes once the chunk is past `config.lodDistance` (renderScene). Same
-   *  textures as bark/leaf/needle/rock. Bushes/flowers have no far version. */
+   *  textures as bark/birch/leaf/needle/rock. Bushes/flowers have no far version. */
   barkFar: Mesh
+  birchBarkFar: Mesh
   leafFar: Mesh
   needleFar: Mesh
   rockFar: Mesh
@@ -231,21 +235,27 @@ function buildChunks(trees: Tree[], boulders: Boulder[], bushes: Bush[], flowers
       const z1 = z0 + cell
       const grass = mesh()
       const bark = mesh()
+      const birchBark = mesh()
       const leaf = mesh()
       const needle = mesh()
       const rock = mesh()
       const flowerMesh = mesh()
       const barkFar = mesh()
+      const birchBarkFar = mesh()
       const leafFar = mesh()
       const needleFar = mesh()
       const rockFar = mesh()
       Terrain.patch(TERRAIN, grass, x0, z0, x1, z1, TERRAIN_SUBDIV, TERRAIN_SUBDIV, GROUND_UV)
       for (const tree of trees) {
         if (inCell(tree.position, x0, z0, x1, z1)) {
-          const foliage = tree.kind === "oak" ? leaf : needle
-          const foliageFar = tree.kind === "oak" ? leafFar : needleFar
-          Tree.build(tree, bark, foliage)
-          Tree.build(tree, barkFar, foliageFar, "impostor")
+          // Birch trunks go to their own white-bark mesh; oak + birch share the oak
+          // leaf foliage, spruce keeps its needles.
+          const trunk = tree.kind === "birch" ? birchBark : bark
+          const trunkFar = tree.kind === "birch" ? birchBarkFar : barkFar
+          const foliage = tree.kind === "spruce" ? needle : leaf
+          const foliageFar = tree.kind === "spruce" ? needleFar : leafFar
+          Tree.build(tree, trunk, foliage)
+          Tree.build(tree, trunkFar, foliageFar, "impostor")
         }
       }
       for (const boulder of boulders) {
@@ -265,11 +275,11 @@ function buildChunks(trees: Tree[], boulders: Boulder[], bushes: Bush[], flowers
           Flower.build(flower, flowerMesh)
         }
       }
-      const b = bounds([grass, bark, leaf, needle, rock, flowerMesh])
+      const b = bounds([grass, bark, birchBark, leaf, needle, rock, flowerMesh])
       if (b === null) {
         continue
       }
-      chunks.push({ ...b, grass, bark, leaf, needle, rock, flowers: flowerMesh, barkFar, leafFar, needleFar, rockFar })
+      chunks.push({ ...b, grass, bark, birchBark, leaf, needle, rock, flowers: flowerMesh, barkFar, birchBarkFar, leafFar, needleFar, rockFar })
     }
   }
   return chunks
@@ -320,7 +330,8 @@ function placeTrees(colliders: Aabb[]): Tree[] {
     if (Math.max(Math.abs(x), Math.abs(z)) < TERRAIN.inner + 3) {
       continue
     }
-    const kind = rand() < 0.5 ? "oak" : "spruce"
+    const roll = rand()
+    const kind = roll < 0.4 ? "oak" : roll < 0.72 ? "spruce" : "birch"
     const growth = 0.08 + rand() * 0.92
     const position = { x, y: Terrain.height(TERRAIN, x, z), z }
     trees.push({ kind, position, growth, seed: (rand() * 0xFFFFFFFF) | 0 })

app/main.ts

@@ -161,8 +161,8 @@ async function main(): Promise<void> {
       t += c.grass.indices.length + c.flowers.indices.length
       const far = chunkFar(c, cam.position, config.lodDistance)
       t += far
-        ? c.barkFar.indices.length + c.leafFar.indices.length + c.needleFar.indices.length + c.rockFar.indices.length
-        : c.bark.indices.length + c.leaf.indices.length + c.needle.indices.length + c.rock.indices.length
+        ? c.barkFar.indices.length + c.birchBarkFar.indices.length + c.leafFar.indices.length + c.needleFar.indices.length + c.rockFar.indices.length
+        : c.bark.indices.length + c.birchBark.indices.length + c.leaf.indices.length + c.needle.indices.length + c.rock.indices.length
     }
     return (t / 3) | 0
   }

app/renderScene.ts

@@ -104,11 +104,13 @@ export function renderBand(
     if (chunkFar(c, camera.position, config.lodDistance)) {
       Rasterizer.draw(fb, c.rockFar, tx.rock, viewProj, config, true, y0, y1)
       Rasterizer.draw(fb, c.barkFar, tx.bark, viewProj, config, true, y0, y1)
+      Rasterizer.draw(fb, c.birchBarkFar, tx.birch, viewProj, config, true, y0, y1)
       Rasterizer.draw(fb, c.leafFar, tx.leaf, viewProj, config, true, y0, y1)
       Rasterizer.draw(fb, c.needleFar, tx.needle, viewProj, config, true, y0, y1)
     } else {
       Rasterizer.draw(fb, c.rock, tx.rock, viewProj, config, true, y0, y1)
       Rasterizer.draw(fb, c.bark, tx.bark, viewProj, config, true, y0, y1)
+      Rasterizer.draw(fb, c.birchBark, tx.birch, viewProj, config, true, y0, y1)
       Rasterizer.draw(fb, c.leaf, tx.leaf, viewProj, config, true, y0, y1)
       Rasterizer.draw(fb, c.needle, tx.needle, viewProj, config, true, y0, y1)
       Rasterizer.draw(fb, c.flowers, tx.flower, viewProj, config, false, y0, y1)

engine/scene/Tree.ts

@@ -7,7 +7,7 @@ const TAU = Math.PI * 2
  *  scales height and girth and adds canopy blobs (oak) / tiers (spruce). `seed`
  *  drives the per-tree random wobble so a forest doesn't look cloned. */
 export type Tree = {
-  kind: "oak" | "spruce"
+  kind: "oak" | "spruce" | "birch"
   /** Trunk base, sitting on the ground. */
   position: Vec3
   growth: number
@@ -34,8 +34,10 @@ export namespace Tree {
     const rand = rng(tree.seed)
     if (tree.kind === "oak") {
       oak(tree.position, tree.growth, rand, trunk, foliage, lod)
-    } else {
+    } else if (tree.kind === "spruce") {
       spruce(tree.position, tree.growth, rand, trunk, foliage, lod)
+    } else {
+      birch(tree.position, tree.growth, rand, trunk, foliage, lod)
     }
   }
 
@@ -101,6 +103,48 @@ export namespace Tree {
     }
   }
 
+  function birch(base: Vec3, g: number, rand: () => number, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"): void {
+    // Silver birch: tall, slender, near-straight white trunk under an airy, high,
+    // slightly drooping canopy of small leaf tufts -- a lean silhouette between the
+    // broad oak and the conical spruce (the white bark texture does the rest).
+    const h = lerp(1, 8.5, g)
+    const rTrunk = lerp(0.03, 0.16, g)
+    const canopyY = base.y + h * 0.75
+    const blobR = h * 0.22
+    if (lod === "impostor") {
+      limb(trunk, base, { x: base.x, y: base.y + h * 0.9, z: base.z }, rTrunk, rTrunk * 0.5, 3)
+      blob(leaves, { x: base.x, y: canopyY, z: base.z }, blobR * 1.1, rand, 4, 2)
+      return
+    }
+    limb(trunk, base, { x: base.x, y: base.y + h * 0.88, z: base.z }, rTrunk, rTrunk * 0.35, 5)
+
+    const spread = h * 0.22
+    // Sparse small blobs clustered high, biased downward so the crown droops.
+    const blobs = 2 + Math.round(g * 2)
+    for (let i = 0; i < blobs; i++) {
+      const angle = rand() * TAU
+      const rad = i === 0 ? 0 : spread * (0.5 + rand() * 0.5)
+      const center = {
+        x: base.x + Math.cos(angle) * rad,
+        y: canopyY + (rand() - 0.6) * spread,
+        z: base.z + Math.sin(angle) * rad,
+      }
+      blob(leaves, center, blobR * (0.7 + rand() * 0.4), rand)
+    }
+    // Grown birches trail a few thin, near-horizontal drooping twigs.
+    if (g > 0.5) {
+      const branches = 2 + Math.round(rand())
+      for (let i = 0; i < branches; i++) {
+        const angle = rand() * TAU
+        const dir = Vec3.normalize({ x: Math.cos(angle), y: 0.6, z: Math.sin(angle) })
+        const start = { x: base.x, y: base.y + h * 0.7, z: base.z }
+        const end = Vec3.add(start, Vec3.scale(dir, h * 0.22))
+        limb(trunk, start, end, rTrunk * 0.4, rTrunk * 0.15, 4)
+        blob(leaves, end, blobR * 0.55, rand)
+      }
+    }
+  }
+
   /** A tapered tube between two points (trunk or branch), `sides`-gonal. */
   function limb(mesh: Mesh, a: Vec3, b: Vec3, ra: number, rb: number, sides: number): void {
     const axis = Vec3.normalize(Vec3.sub(b, a))

scripts/gen-assets.ts

@@ -126,6 +126,18 @@ const bark: Shade = (x, y) => {
   return [92 + n + grain + crack, 66 + n * 0.8 + grain * 0.6 + crack, 44 + n * 0.6 + crack, 255]
 }
 
+// Silver birch bark: papery near-white with faint grey mottle and the dark
+// horizontal lenticel dashes that make a birch read as a birch.
+const birch: Shade = (x, y) => {
+  const n = noise(x, y) * 8
+  // Dark dashes: short random runs on a few rows, wrapping the trunk horizontally.
+  if (y % 8 < 3 && noise(Math.floor(x / 6), Math.floor(y / 8)) > 0.3) {
+    return [38 + n, 38 + n, 40 + n, 255]
+  }
+  const smudge = noise(Math.floor(x / 10), Math.floor(y / 10)) < -0.4 ? -22 : 0
+  return [216 + n + smudge, 218 + n + smudge, 214 + n + smudge, 255]
+}
+
 // Oak leaves: mid green, blotchy clumps with brighter highlights.
 const leaf: Shade = (x, y) => {
   const n = noise(x, y) * 26
@@ -249,6 +261,7 @@ const assets: Array<[string, number, number, Shade]> = [
   ["floor", 64, 64, floor],
   ["grass", 64, 64, grass],
   ["bark", 64, 64, bark],
+  ["birch", 64, 64, birch],
   ["leaf", 64, 64, leaf],
   ["needle", 64, 64, needle],
   ["rock", 64, 64, rock],