233 lines
9.6 KiB
TypeScript
233 lines
9.6 KiB
TypeScript
import { Vec3 } from "../math/Vec3"
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import { STRIDE, type Mesh } from "./Mesh"
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const TAU = Math.PI * 2
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/** One procedural tree instance. `growth` 0..1 runs sapling -> full grown: it
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* scales height and girth and adds canopy blobs (oak) / tiers (spruce). `seed`
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* drives the per-tree random wobble so a forest doesn't look cloned. */
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export type Tree = {
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kind: "oak" | "spruce" | "birch"
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/** Trunk base, sitting on the ground. */
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position: Vec3
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growth: number
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seed: number
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}
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/**
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* Low-poly tree geometry, in the same faceted flat-shaded style as the rest of
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* the world. Two silhouettes carry the species read:
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* oak -- short tapered trunk, a couple of branches, a broad cluster of
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* rounded canopy blobs (bushy, wider than tall).
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* spruce -- tall thin trunk under stacked cones that narrow to a point
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* (tiered, taller than wide).
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* `build` appends into caller-owned meshes so a whole forest batches into a few
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* draw calls: all trunks share one bark mesh, foliage splits oak vs spruce so
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* each can carry its own leaf/needle texture.
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*/
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export namespace Tree {
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/** Append one tree into the shared `trunk` (bark) mesh and the `foliage` mesh
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* for its kind (oak leaf vs spruce needle). */
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/** `lod` "impostor" bakes a much cheaper stand-in (few tris, same textures +
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* faceted look, same height/position) for far chunks; "full" is up close. */
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export function build(tree: Tree, trunk: Mesh, foliage: Mesh, lod: "full" | "impostor" = "full"): void {
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const rand = rng(tree.seed)
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if (tree.kind === "oak") {
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oak(tree.position, tree.growth, rand, trunk, foliage, lod)
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} else if (tree.kind === "spruce") {
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spruce(tree.position, tree.growth, rand, trunk, foliage, lod)
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} else {
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birch(tree.position, tree.growth, rand, trunk, foliage, lod)
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}
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}
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function oak(base: Vec3, g: number, rand: () => number, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"): void {
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const h = lerp(0.8, 7, g)
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const rTrunk = lerp(0.04, 0.32, g)
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const forkY = base.y + h * 0.5
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const canopyY = base.y + h * 0.72
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const blobR = h * 0.3
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if (lod === "impostor") {
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// One low-poly blob on a stubby trunk -- reads as an oak at distance.
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limb(trunk, base, { x: base.x, y: forkY, z: base.z }, rTrunk, rTrunk * 0.6, 3)
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blob(leaves, { x: base.x, y: canopyY, z: base.z }, blobR * 1.15, rand, 4, 2)
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return
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}
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limb(trunk, base, { x: base.x, y: forkY, z: base.z }, rTrunk, rTrunk * 0.6, 5)
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const spread = h * 0.32
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// Central blob plus, as it grows, a couple offset ones -> broad bushy crown.
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const blobs = 1 + Math.round(g * 2)
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for (let i = 0; i < blobs; i++) {
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const angle = rand() * TAU
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const rad = i === 0 ? 0 : spread * (0.5 + rand() * 0.5)
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const center = {
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x: base.x + Math.cos(angle) * rad,
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y: canopyY + (rand() - 0.4) * spread,
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z: base.z + Math.sin(angle) * rad,
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}
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blob(leaves, center, blobR * (0.7 + rand() * 0.4), rand)
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}
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// Grown oaks throw out a few branches, each tipped with a leaf tuft.
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if (g > 0.55) {
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const branches = 2 + Math.round(rand())
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for (let i = 0; i < branches; i++) {
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const angle = rand() * TAU
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const dir = Vec3.normalize({ x: Math.cos(angle), y: 1.2, z: Math.sin(angle) })
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const start = { x: base.x, y: base.y + h * 0.42, z: base.z }
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const end = Vec3.add(start, Vec3.scale(dir, h * 0.3))
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limb(trunk, start, end, rTrunk * 0.4, rTrunk * 0.2, 4)
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blob(leaves, end, blobR * 0.6, rand)
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}
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}
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}
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function spruce(base: Vec3, g: number, rand: () => number, trunk: Mesh, needles: Mesh, lod: "full" | "impostor"): void {
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const h = lerp(0.6, 9, g)
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const rTrunk = lerp(0.03, 0.2, g)
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const impostor = lod === "impostor"
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limb(trunk, base, { x: base.x, y: base.y + h, z: base.z }, rTrunk, rTrunk * 0.25, impostor ? 3 : 5)
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// Stacked cones: widest low, shrinking to a point up top -> conical tiers.
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// The impostor keeps the first two tiers at low sides (same seed => aligned).
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const tiers = impostor ? 2 : 2 + Math.round(g * 3)
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const sides = impostor ? 4 : 6
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const bottom = base.y + h * 0.1
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const span = h * 0.9
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for (let i = 0; i < tiers; i++) {
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const t = i / tiers
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const y = bottom + t * span * 0.82
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const radius = lerp(h * 0.3, h * 0.05, t) * (0.9 + rand() * 0.2)
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const coneH = (span / tiers) * 1.9
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cone(needles, { x: base.x, y, z: base.z }, coneH, radius, sides)
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}
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}
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function birch(base: Vec3, g: number, rand: () => number, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"): void {
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// Silver birch: tall, slender, near-straight white trunk under an airy, high,
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// slightly drooping canopy of small leaf tufts -- a lean silhouette between the
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// broad oak and the conical spruce (the white bark texture does the rest).
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const h = lerp(1, 8.5, g)
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const rTrunk = lerp(0.03, 0.16, g)
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const canopyY = base.y + h * 0.75
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const blobR = h * 0.22
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if (lod === "impostor") {
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limb(trunk, base, { x: base.x, y: base.y + h * 0.9, z: base.z }, rTrunk, rTrunk * 0.5, 3)
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blob(leaves, { x: base.x, y: canopyY, z: base.z }, blobR * 1.1, rand, 4, 2)
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return
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}
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limb(trunk, base, { x: base.x, y: base.y + h * 0.88, z: base.z }, rTrunk, rTrunk * 0.35, 5)
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const spread = h * 0.22
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// Sparse small blobs clustered high, biased downward so the crown droops.
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const blobs = 2 + Math.round(g * 2)
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for (let i = 0; i < blobs; i++) {
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const angle = rand() * TAU
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const rad = i === 0 ? 0 : spread * (0.5 + rand() * 0.5)
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const center = {
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x: base.x + Math.cos(angle) * rad,
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y: canopyY + (rand() - 0.6) * spread,
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z: base.z + Math.sin(angle) * rad,
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}
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blob(leaves, center, blobR * (0.7 + rand() * 0.4), rand)
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}
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// Grown birches trail a few thin, near-horizontal drooping twigs.
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if (g > 0.5) {
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const branches = 2 + Math.round(rand())
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for (let i = 0; i < branches; i++) {
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const angle = rand() * TAU
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const dir = Vec3.normalize({ x: Math.cos(angle), y: 0.6, z: Math.sin(angle) })
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const start = { x: base.x, y: base.y + h * 0.7, z: base.z }
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const end = Vec3.add(start, Vec3.scale(dir, h * 0.22))
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limb(trunk, start, end, rTrunk * 0.4, rTrunk * 0.15, 4)
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blob(leaves, end, blobR * 0.55, rand)
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}
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}
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}
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/** A tapered tube between two points (trunk or branch), `sides`-gonal. */
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function limb(mesh: Mesh, a: Vec3, b: Vec3, ra: number, rb: number, sides: number): void {
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const axis = Vec3.normalize(Vec3.sub(b, a))
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const [u, v] = basis(axis)
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const len = Vec3.length(Vec3.sub(b, a))
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const start = mesh.verts.length / STRIDE
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for (let i = 0; i <= sides; i++) {
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const angle = (i / sides) * TAU
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const dx = u.x * Math.cos(angle) + v.x * Math.sin(angle)
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const dy = u.y * Math.cos(angle) + v.y * Math.sin(angle)
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const dz = u.z * Math.cos(angle) + v.z * Math.sin(angle)
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const s = i / sides
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mesh.verts.push(a.x + dx * ra, a.y + dy * ra, a.z + dz * ra, s * 1.5, 0)
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mesh.verts.push(b.x + dx * rb, b.y + dy * rb, b.z + dz * rb, s * 1.5, len * 0.5)
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}
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for (let i = 0; i < sides; i++) {
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const p = start + i * 2
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mesh.indices.push(p, p + 2, p + 3, p, p + 3, p + 1)
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}
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}
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/** A cone standing on a base ring, apex `height` above it (one spruce tier). */
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function cone(mesh: Mesh, base: Vec3, height: number, radius: number, sides: number): void {
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const start = mesh.verts.length / STRIDE
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mesh.verts.push(base.x, base.y + height, base.z, 0.5, 0)
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for (let i = 0; i <= sides; i++) {
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const angle = (i / sides) * TAU
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mesh.verts.push(base.x + Math.cos(angle) * radius, base.y, base.z + Math.sin(angle) * radius, (i / sides) * 2, 1)
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}
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for (let i = 0; i < sides; i++) {
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// Wound so the outer surface faces out, matching the backface-cull sign.
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mesh.indices.push(start, start + 2 + i, start + 1 + i)
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}
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}
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/** A lumpy low-poly sphere (one oak canopy blob). Per-ring radius wobble keeps
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* it organic without cracking the longitude seam. */
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function blob(mesh: Mesh, center: Vec3, radius: number, rand: () => number, seg = 5, rings = 3): void {
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const start = mesh.verts.length / STRIDE
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for (let r = 0; r <= rings; r++) {
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const phi = (r / rings) * Math.PI
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const cy = Math.cos(phi)
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const cr = Math.sin(phi)
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const scale = radius * (0.85 + rand() * 0.3)
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for (let s = 0; s <= seg; s++) {
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const theta = (s / seg) * TAU
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mesh.verts.push(
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center.x + cr * Math.cos(theta) * scale,
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center.y + cy * scale,
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center.z + cr * Math.sin(theta) * scale,
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(s / seg) * 2,
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(r / rings) * 2,
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)
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}
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}
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const row = seg + 1
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for (let r = 0; r < rings; r++) {
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for (let s = 0; s < seg; s++) {
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const p = start + r * row + s
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mesh.indices.push(p, p + 1, p + row + 1, p, p + row + 1, p + row)
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}
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}
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}
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/** Two unit vectors spanning the plane perpendicular to `axis`. */
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function basis(axis: Vec3): [Vec3, Vec3] {
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const ref = Math.abs(axis.y) < 0.99 ? { x: 0, y: 1, z: 0 } : { x: 1, y: 0, z: 0 }
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const u = Vec3.normalize(Vec3.cross(ref, axis))
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return [u, Vec3.cross(axis, u)]
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}
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function lerp(a: number, b: number, t: number): number {
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return a + (b - a) * t
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}
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/** Deterministic 0..1 generator (mulberry32) seeded per tree. */
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function rng(seed: number): () => number {
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let a = seed >>> 0
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return () => {
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a = (a + 0x6D2B79F5) | 0
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let t = Math.imul(a ^ (a >>> 15), 1 | a)
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t ^= t + Math.imul(t ^ (t >>> 7), 61 | t)
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return ((t ^ (t >>> 14)) >>> 0) / 4294967296
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}
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}
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}
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