feat: foilage

engine/scene/Bush.ts

@@ -0,0 +1,76 @@
+import type { Vec3 } from "../math/Vec3"
+import { STRIDE, type Mesh } from "./Mesh"
+
+const TAU = Math.PI * 2
+
+/** A low shrub: a tight cluster of small leafy blobs sitting on the ground.
+ *  Textured with the same leaf sheet as oak canopies, so it batches into the
+ *  chunk's foliage mesh. `size` is the overall spread; `seed` the per-bush wobble. */
+export type Bush = {
+  position: Vec3
+  size: number
+  seed: number
+}
+
+/** Low-poly bush geometry, same faceted flat-shaded style as the trees. A few
+ *  overlapping jittered spheres read as a rounded shrub; blobs are closed and
+ *  wound outward, so backface culling is safe. `build` appends into a shared
+ *  (leaf-textured) mesh. */
+export namespace Bush {
+  export function build(bush: Bush, mesh: Mesh): void {
+    const rand = rng(bush.seed)
+    // A handful of smaller overlapping lumps reads as a soft shrub; one big
+    // sphere reads as a boulder.
+    const blobs = 3 + Math.floor(rand() * 3)
+    const r = bush.size * 0.42
+    for (let i = 0; i < blobs; i++) {
+      const angle = rand() * TAU
+      const dist = i === 0 ? 0 : bush.size * 0.5 * rand()
+      const cx = bush.position.x + Math.cos(angle) * dist
+      const cz = bush.position.z + Math.sin(angle) * dist
+      const cy = bush.position.y + r * (0.5 + rand() * 0.4)
+      blob(mesh, cx, cy, cz, r * (0.55 + rand() * 0.3), rand)
+    }
+  }
+
+  /** A small lumpy low-poly sphere, wound outward (matches the oak canopy blob). */
+  function blob(mesh: Mesh, cx: number, cy: number, cz: number, radius: number, rand: () => number): void {
+    const seg = 6
+    const rings = 4
+    const start = mesh.verts.length / STRIDE
+    for (let r = 0; r <= rings; r++) {
+      const phi = (r / rings) * Math.PI
+      const cyv = Math.cos(phi)
+      const crv = Math.sin(phi)
+      const scale = radius * (0.9 + rand() * 0.18)
+      for (let s = 0; s <= seg; s++) {
+        const theta = (s / seg) * TAU
+        mesh.verts.push(
+          cx + crv * Math.cos(theta) * scale,
+          cy + cyv * scale,
+          cz + crv * Math.sin(theta) * scale,
+          (s / seg) * 2,
+          (r / rings) * 2,
+        )
+      }
+    }
+    const row = seg + 1
+    for (let r = 0; r < rings; r++) {
+      for (let s = 0; s < seg; s++) {
+        const p = start + r * row + s
+        mesh.indices.push(p, p + 1, p + row + 1, p, p + row + 1, p + row)
+      }
+    }
+  }
+
+  /** Deterministic 0..1 generator (mulberry32) seeded per bush. */
+  function rng(seed: number): () => number {
+    let a = seed >>> 0
+    return () => {
+      a = (a + 0x6D2B79F5) | 0
+      let t = Math.imul(a ^ (a >>> 15), 1 | a)
+      t ^= t + Math.imul(t ^ (t >>> 7), 61 | t)
+      return ((t ^ (t >>> 14)) >>> 0) / 4294967296
+    }
+  }
+}