three.js/examples/jsm/generators/TreeGenerator.js

import {
	BufferAttribute,
	BufferGeometry,
	Mesh,
	Vector3
} from 'three';

import { MeshStandardNodeMaterial } from 'three/webgpu';
import { color, float, mx_fractal_noise_float, positionLocal, vec3 } from 'three/tsl';

// the golden angle ( 137.5° ): rolling each sibling branch by this much around the
// parent axis spreads them like a real stem, so they never line up
const GOLDEN_ANGLE = Math.PI * ( 3 - Math.sqrt( 5 ) );
const DEG2RAD = Math.PI / 180;
const TAU = Math.PI * 2;

const UP = /*@__PURE__*/ new Vector3( 0, 1, 0 );
const _axis = /*@__PURE__*/ new Vector3();

// reusable scratch for one tube's ring vertices ( grows to the largest tube seen )
let _ring = new Float32Array( 0 );

/**
 * Grows a procedural tree skeleton — trunk, branches and twigs, each swept as a tapered
 * tube — and bakes it into one non-indexed {@link BufferGeometry} (position and normal
 * only), ready to instance into a forest. It produces *branches only*; add foliage as a
 * separate layer.
 *
 * The branching is deterministic for a given `seed`: a recursive sweep lays down gently
 * curved tubes with a parallel-transport frame (so they never twist), forking by the
 * pipe model (each child much thinner than its parent), spreading children along the
 * upper part of each branch with a golden-angle roll, and pulling them back up toward
 * the light. A flared root, non-linear taper and gravity droop fill in the character.
 *
 * Parameters are set with a fluent builder: a `set<Param>()` exists for every default
 * ( `setSeed`, `setLevels`, `setChildren`, … ), each returning `this` for chaining.
 *
 * Each `build()` returns a fresh, independent mesh that the caller owns, so one
 * generator can be re-parametrized and built repeatedly to grow a varied stand:
 *
 * ```js
 * const generator = new TreeGenerator( material );
 * const oak = generator.setSeed( 1 ).setLevels( 4 ).build();
 * const pine = generator.setSeed( 2 ).setLevels( 5 ).build();
 * ```
 */
class TreeGenerator {

	constructor( material = null ) {

		this.material = material;
		this.parameters = {}; // overrides; defaults fill the rest at build time

	}

	build() {

		const p = Object.assign( {}, TreeGenerator.defaults, this.parameters );
		const random = createRandom( p.seed );

		// grow the skeleton into a flat list of tubes, then size and fill the geometry in
		// one pass — no per-vertex objects, no array growth

		const tubes = [];
		growBranch( tubes, new Vector3(), UP, p.trunkLength, p.trunkRadius, 0, p, random );

		let vertexCount = 0;
		for ( const tube of tubes ) vertexCount += ( tube.rings.length - 1 ) * tube.radial * 6;

		const positions = new Float32Array( vertexCount * 3 );
		const normals = new Float32Array( vertexCount * 3 );

		let offset = 0;
		for ( const tube of tubes ) offset = emitTube( positions, normals, offset, tube.rings, tube.radial );

		const geometry = new BufferGeometry();
		geometry.setAttribute( 'position', new BufferAttribute( positions, 3 ) );
		geometry.setAttribute( 'normal', new BufferAttribute( normals, 3 ) );
		geometry.computeBoundingSphere();

		const mesh = new Mesh( geometry, this.material || createTreeMaterial() );
		mesh.name = 'Tree';

		return mesh;

	}

}

TreeGenerator.defaults = {
	seed: 1,
	levels: 4, // recursion depth: trunk, branch, twig, sub-twig
	children: [ 3, 12, 8 ], // sub-branches per level; density comes from many children spread along each parent, not depth
	branchAngle: [ 38, 50, 58 ], // degrees a child tilts off its parent axis, per level
	angleVariance: 14, // degrees of random jitter on the branch angle, breaks fractal regularity
	lengthRatio: 0.62, // child length / parent length
	trunkLength: 9, // trunk length in world units; sets the tree's height
	trunkRadius: 0.42, // base radius of the trunk
	taper: 0.55, // a branch thins to ( 1 - taper ) of its base radius along its own length
	taperCurve: 0.7, // < 1 keeps the bole full then tapers ( real trees ), 1 = straight cone
	rootFlare: 0.6, // how much the trunk swells at the very base
	flareFrac: 0.18, // fraction of the trunk over which the flare acts
	radiusExponent: 2.3, // pipe model ( da Vinci ): childBase = parentBase × ( 1 / children )^( 1 / radiusExponent )
	minRadius: 0.05, // hair-thin floor so twigs don't taper to a sliver
	minLength: 0.6, // branches shorter than this stop recursing
	droop: 0.05, // gravity sag per branch ( ≈ droop × length ); the trunk stays upright
	upPull: 0.3, // phototropism: 0 = a bare spread cone ( many branches aim down ), 1 = straight up
	gnarl: [ 0.05, 0.16, 0.26, 0.32 ], // per-level random wobble on each tube segment
	radialSegments: 6, // ring vertices around a tube ( drops by one per level for thin twigs )
	sectionLength: 1.3, // world units per tube segment, so a tall trunk stays smooth
	childStart: 0.12, // fraction up a sub-branch before children appear
	trunkClear: 0.25 // fraction of the trunk kept bare before the crown ( raise for a tall clean bole )
};

// a fluent setter for every default — setSeed(), setLevels(), setChildren(), … — each
// storing its value and returning `this`, so the API stays in sync with the parameters
for ( const key of Object.keys( TreeGenerator.defaults ) ) {

	TreeGenerator.prototype[ 'set' + key[ 0 ].toUpperCase() + key.slice( 1 ) ] = function ( value ) {

		this.parameters[ key ] = value;
		return this;

	};

}

// --- skeleton ------------------------------------------------------------

// Grows one branch as a gently curved, tapered tube and recurses, collecting the tube
// into `tubes`. The tube is swept with a parallel-transport frame ( rotated by the same
// rotation that bends the tangent each step ) so it never twists, unlike a naive Frenet
// frame. Children fork off the upper part of the branch by the pipe model.
function growBranch( tubes, base, dir, length, baseRadius, level, p, random ) {

	const sections = Math.max( 3, Math.min( 24, Math.round( length / p.sectionLength ) ) ); // ring count tracks length
	const radial = Math.max( 3, p.radialSegments - level );
	const step = length / sections;
	const gnarl = p.gnarl[ Math.min( level, p.gnarl.length - 1 ) ];
	const start = level === 0 ? p.trunkClear : p.childStart; // the trunk carries a clean bole below its crown

	let tangent = dir.clone().normalize();
	const normal = perpendicular( tangent );

	const rings = [];
	const pos = base.clone();

	for ( let s = 0; s <= sections; s ++ ) {

		const t = s / sections;

		// non-linear taper down to ( 1 - taper ) of the base, with a flared root on the trunk
		let radius = baseRadius * ( ( 1 - p.taper ) + p.taper * Math.pow( 1 - t, p.taperCurve ) );
		if ( level === 0 && p.rootFlare > 0 ) {

			const flare = Math.max( 0, ( p.flareFrac - t ) / p.flareFrac );
			radius *= 1 + p.rootFlare * flare * flare * flare; // sharp knee, confined to the base

		}

		rings.push( {
			pos: pos.clone(),
			tangent: tangent.clone(),
			normal: normal.clone(),
			binormal: new Vector3().crossVectors( tangent, normal ),
			radius
		} );

		if ( s < sections ) {

			const next = tangent.clone();
			next.x += ( random() * 2 - 1 ) * gnarl;
			next.y += ( random() * 2 - 1 ) * gnarl;
			next.z += ( random() * 2 - 1 ) * gnarl;
			if ( level > 0 ) next.y -= p.droop * step; // branches sag; the trunk stays vertical
			next.normalize();

			transport( tangent, next, normal ); // keep the frame torsion-free
			pos.addScaledVector( next, step );
			tangent = next;

		}

	}

	tubes.push( { rings, radial } );

	if ( level >= p.levels - 1 || length < p.minLength ) return;

	// fork: children spread along the upper branch, each tilted off the local tangent,
	// rolled by the golden angle, and much thinner than the parent ( pipe model )

	const n = p.children[ Math.min( level, p.children.length - 1 ) ];
	const angle = p.branchAngle[ Math.min( level, p.branchAngle.length - 1 ) ];
	const pipeDrop = Math.pow( 1 / n, 1 / p.radiusExponent );

	for ( let i = 0; i < n; i ++ ) {

		const t = start + ( i + 0.5 + ( random() - 0.5 ) * 0.6 ) / n * ( 1 - start );
		const ring = ringAt( rings, t );

		const tilt = ( angle + ( random() * 2 - 1 ) * p.angleVariance ) * DEG2RAD;
		const roll = i * GOLDEN_ANGLE + ( random() * 2 - 1 ) * 0.4;

		// tilt off a perpendicular axis FIRST, then roll about the parent axis, then pull
		// back toward the light ( else the roll sends half the children downward )
		const childDir = ring.tangent.clone()
			.applyAxisAngle( ring.normal, tilt )
			.applyAxisAngle( ring.tangent, roll );
		if ( p.upPull > 0 ) childDir.lerp( UP, p.upPull ).normalize();

		// the pipe-model drop, but never fatter than the wood it leaves nor below the floor
		const childBase = Math.max( p.minRadius, Math.min( baseRadius * pipeDrop, ring.radius ) );

		growBranch( tubes, ring.pos, childDir, length * p.lengthRatio, childBase, level + 1, p, random );

	}

}

// a unit vector perpendicular to v ( cross with the least-aligned axis )
function perpendicular( v ) {

	const a = Math.abs( v.x ) < 0.9 ? _axis.set( 1, 0, 0 ) : _axis.set( 0, 1, 0 );
	return new Vector3().crossVectors( v, a ).normalize();

}

// rotate frame vector n by the rotation that maps tangent t0 onto t1
function transport( t0, t1, n ) {

	_axis.crossVectors( t0, t1 );
	const sin = _axis.length();
	if ( sin < 1e-6 ) return; // already parallel
	_axis.divideScalar( sin );
	n.applyAxisAngle( _axis, Math.atan2( sin, t0.dot( t1 ) ) );

}

// sample the branch frame at fraction t ( 0..1 ) for spawning a child
function ringAt( rings, t ) {

	const f = Math.max( 0, Math.min( 0.999, t ) ) * ( rings.length - 1 );
	const i = Math.floor( f );
	const frac = f - i;
	const a = rings[ i ];
	const b = rings[ Math.min( i + 1, rings.length - 1 ) ];

	return {
		pos: a.pos.clone().lerp( b.pos, frac ),
		tangent: a.tangent.clone().lerp( b.tangent, frac ).normalize(),
		normal: a.normal.clone().lerp( b.normal, frac ).normalize(),
		radius: a.radius + ( b.radius - a.radius ) * frac
	};

}

// --- geometry ------------------------------------------------------------

// Sweeps a tube through the rings: each ring is a loop of `radial` vertices in its
// ( normal, binormal ) plane, the outward radial direction being the vertex normal.
// Ring vertices are computed once into a reused scratch, then stitched straight into the
// preallocated geometry arrays — no per-vertex objects.
function emitTube( positions, normals, offset, rings, radial ) {

	const stride = ( radial + 1 ) * 6; // one ring loop: ( position, normal ) per vertex
	const needed = rings.length * stride;
	if ( _ring.length < needed ) _ring = new Float32Array( needed );

	const ring = _ring;

	for ( let r = 0; r < rings.length; r ++ ) {

		const { pos, normal, binormal, radius } = rings[ r ];
		let o = r * stride;

		for ( let j = 0; j <= radial; j ++ ) {

			const a = j / radial * TAU;
			const c = Math.cos( a );
			const s = Math.sin( a );
			const nx = c * normal.x + s * binormal.x;
			const ny = c * normal.y + s * binormal.y;
			const nz = c * normal.z + s * binormal.z;

			ring[ o ++ ] = pos.x + nx * radius;
			ring[ o ++ ] = pos.y + ny * radius;
			ring[ o ++ ] = pos.z + nz * radius;
			ring[ o ++ ] = nx;
			ring[ o ++ ] = ny;
			ring[ o ++ ] = nz;

		}

	}

	// stitch consecutive rings into quads ( two triangles ), wound so normals face out

	for ( let r = 0; r < rings.length - 1; r ++ ) {

		const a = r * stride;
		const b = ( r + 1 ) * stride;

		for ( let j = 0; j < radial; j ++ ) {

			const aL = a + j * 6, aR = a + ( j + 1 ) * 6;
			const bL = b + j * 6, bR = b + ( j + 1 ) * 6;

			offset = copyVertex( positions, normals, offset, ring, aL );
			offset = copyVertex( positions, normals, offset, ring, bR );
			offset = copyVertex( positions, normals, offset, ring, bL );

			offset = copyVertex( positions, normals, offset, ring, aL );
			offset = copyVertex( positions, normals, offset, ring, aR );
			offset = copyVertex( positions, normals, offset, ring, bR );

		}

	}

	return offset;

}

// copies one ( position, normal ) vertex from the ring scratch into the geometry arrays
function copyVertex( positions, normals, offset, ring, i ) {

	const o = offset * 3;
	positions[ o ] = ring[ i ]; positions[ o + 1 ] = ring[ i + 1 ]; positions[ o + 2 ] = ring[ i + 2 ];
	normals[ o ] = ring[ i + 3 ]; normals[ o + 1 ] = ring[ i + 4 ]; normals[ o + 2 ] = ring[ i + 5 ];

	return offset + 1;

}

// --- deterministic PRNG ( mulberry32 ) -----------------------------------

function createRandom( seed ) {

	let s = ( seed >>> 0 ) || 1;

	return function () {

		s = ( s + 0x6D2B79F5 ) | 0;
		let t = Math.imul( s ^ ( s >>> 15 ), 1 | s );
		t = ( t + Math.imul( t ^ ( t >>> 7 ), 61 | t ) ) ^ t;
		return ( ( t ^ ( t >>> 14 ) ) >>> 0 ) / 4294967296;

	};

}

// --- material ------------------------------------------------------------

/**
 * A simple bark material for a {@link TreeGenerator} mesh: a low-saturation brown with a
 * faint, vertically-stretched grain, so trunks read near-black against bright fog.
 *
 * @param {Object} [parameters] - `barkColor` ( a hex, THREE.Color or TSL node ).
 * @return {MeshStandardNodeMaterial}
 */
function createTreeMaterial( parameters = {} ) {

	const c = parameters.barkColor;
	const barkColor = c === undefined ? color( 0x4b3a2b ) : ( c.isColor || typeof c === 'number' ? color( c ) : c );

	const material = new MeshStandardNodeMaterial();
	const grain = mx_fractal_noise_float( positionLocal.mul( vec3( 2.5, 0.4, 2.5 ) ), 3 ).mul( 0.18 );
	material.colorNode = barkColor.mul( grain.add( 0.9 ) );
	material.roughnessNode = float( 0.95 );
	material.metalnessNode = float( 0 );

	return material;

}

export { TreeGenerator, createTreeMaterial };