three-mesh-bvh

What is three-mesh-bvh?

The three-mesh-bvh package is a utility for creating and using Bounding Volume Hierarchies (BVH) to accelerate raycasting, intersection testing, and spatial queries on three.js meshes. It is particularly useful for improving performance in complex scenes with many objects or detailed geometries.

What are three-mesh-bvh's main functionalities?

Raycasting

This feature allows you to perform efficient raycasting on a mesh by using a BVH. The code sample demonstrates how to create a BVH for a mesh and override the raycast method to use the accelerated raycasting provided by three-mesh-bvh.

const { MeshBVH, acceleratedRaycast } = require('three-mesh-bvh');
const { Mesh, Raycaster, BoxGeometry, MeshBasicMaterial } = require('three');

// Create a mesh
const geometry = new BoxGeometry(1, 1, 1);
const material = new MeshBasicMaterial({ color: 0x00ff00 });
const mesh = new Mesh(geometry, material);

// Create BVH
mesh.geometry.boundsTree = new MeshBVH(mesh.geometry);

// Override raycast method
mesh.raycast = acceleratedRaycast;

// Perform raycasting
const raycaster = new Raycaster();
raycaster.setFromCamera({ x: 0, y: 0 }, camera);
const intersects = raycaster.intersectObject(mesh);
console.log(intersects);

Intersection Testing

This feature allows you to test for intersections between two geometries using BVH. The code sample demonstrates how to create a BVH for one mesh and check if it intersects with another mesh.

const { MeshBVH, acceleratedRaycast } = require('three-mesh-bvh');
const { Mesh, BoxGeometry, MeshBasicMaterial, Vector3 } = require('three');

// Create two meshes
const geometry1 = new BoxGeometry(1, 1, 1);
const material1 = new MeshBasicMaterial({ color: 0x00ff00 });
const mesh1 = new Mesh(geometry1, material1);

const geometry2 = new BoxGeometry(1, 1, 1);
const material2 = new MeshBasicMaterial({ color: 0xff0000 });
const mesh2 = new Mesh(geometry2, material2);
mesh2.position.set(0.5, 0.5, 0.5);

// Create BVH for the first mesh
mesh1.geometry.boundsTree = new MeshBVH(mesh1.geometry);

// Check for intersection
const intersects = mesh1.geometry.boundsTree.intersectsGeometry(mesh2.geometry, mesh2.matrixWorld);
console.log(intersects);

Spatial Queries

This feature allows you to perform spatial queries, such as checking if a sphere intersects with a mesh, using BVH. The code sample demonstrates how to create a BVH for a mesh and perform a spatial query with a sphere.

const { MeshBVH } = require('three-mesh-bvh');
const { Mesh, BoxGeometry, MeshBasicMaterial, Sphere } = require('three');

// Create a mesh
const geometry = new BoxGeometry(1, 1, 1);
const material = new MeshBasicMaterial({ color: 0x00ff00 });
const mesh = new Mesh(geometry, material);

// Create BVH
mesh.geometry.boundsTree = new MeshBVH(mesh.geometry);

// Define a sphere for spatial query
const sphere = new Sphere(new Vector3(0, 0, 0), 1.5);

// Perform spatial query
const intersects = mesh.geometry.boundsTree.intersectsSphere(sphere);
console.log(intersects);

Other packages similar to three-mesh-bvh

three

The three package is the core library for three.js, which provides a wide range of functionalities for 3D graphics rendering. While it includes basic raycasting and intersection testing, it does not provide the optimized BVH structures that three-mesh-bvh offers for performance improvements.

ammo.js

ammo.js is a physics engine that can be used with three.js for collision detection and physics simulations. It provides broad-phase and narrow-phase collision detection but is more complex and heavier compared to the lightweight and specialized BVH implementation in three-mesh-bvh.

cannon-es

cannon-es is a lightweight 3D physics engine for JavaScript. It provides collision detection and physics simulations, similar to ammo.js, but does not specifically focus on BVH for raycasting and spatial queries like three-mesh-bvh.

README

three-mesh-bvh

A BVH implementation to speed up raycasting and enable spatial queries against three.js meshes.

Casting 500 rays against an 80,000 polygon model at 60fps!

Examples

Raycasting

Skinned geometry

Point cloud interesection

Shape intersection

Geometry edge intersection

SDF generation

WebWorker generation

BVH options inspector

Tools

Sculpting

Distance comparison

Triangle painting

Lasso selection

Clipped edges

Geometry voxelization

Geometry edge projection

Games

Sphere physics collision

Player movement

Path Tracing

Simple GPU Path Tracing

Lambert GPU Path Tracing

CPU Path Tracing

Gem Refraction Path Tracing

External Projects

three-gpu-pathtracer

three-bvh-csg

Use

Using pre-made functions

// Import via ES6 modules
import * as THREE from 'three';
import { computeBoundsTree, disposeBoundsTree, acceleratedRaycast } from 'three-mesh-bvh';

// Or UMD
const { computeBoundsTree, disposeBoundsTree, acceleratedRaycast } = window.MeshBVHLib;


// Add the extension functions
THREE.BufferGeometry.prototype.computeBoundsTree = computeBoundsTree;
THREE.BufferGeometry.prototype.disposeBoundsTree = disposeBoundsTree;
THREE.Mesh.prototype.raycast = acceleratedRaycast;

// Generate geometry and associated BVH
const geom = new THREE.TorusKnotBufferGeometry( 10, 3, 400, 100 );
const mesh = new THREE.Mesh( geom, material );
geom.computeBoundsTree();

Or manually building the BVH

// Import via ES6 modules
import * as THREE from 'three';
import { MeshBVH, acceleratedRaycast } from 'three-mesh-bvh';

// Or UMD
const { MeshBVH, acceleratedRaycast } = window.MeshBVHLib;


// Add the raycast function. Assumes the BVH is available on
// the `boundsTree` variable
THREE.Mesh.prototype.raycast = acceleratedRaycast;

// ...

// Generate the BVH and use the newly generated index
geom.boundsTree = new MeshBVH( geom );

And then raycasting

// Setting "firstHitOnly" to true means the Mesh.raycast function will use the
// bvh "raycastFirst" function to return a result more quickly.
const raycaster = new THREE.Raycaster();
raycaster.firstHitOnly = true;
raycaster.intersectObjects( [ mesh ] );

Querying the BVH Directly

import * as THREE from 'three';
import { MeshBVH, acceleratedRaycast } from 'three-mesh-bvh';

let mesh, geometry;
const invMat = new THREE.Matrix4();

// instantiate the geometry

// ...

const bvh = new MeshBVH( geometry );
invMat.copy( mesh.matrixWorld ).invert();

// raycasting
// ensure the ray is in the local space of the geometry being cast against
raycaster.ray.applyMatrix4( invMat );
const hit = bvh.raycastFirst( raycaster.ray );

// results are returned in local spac, as well, so they must be transformed into
// world space if needed.
hit.point.applyMatrixWorld( mesh.matrixWorld );

// spherecasting
// ensure the sphere is in the local space of the geometry being cast against
sphere.applyMatrix4( invMat );
const intersects = bvh.intersectsSphere( sphere );

With Skinned and Morph Target Meshes

import { StaticGeometryGenerator } from 'three-mesh-bvh';

const generator = new StaticGeometryGenerator( [ ...skinnedMeshes ] );
const geometry = generator.generate();
geometry.computeBoundsTree();

// ...

// update the geometry in place
generator.generate( geometry );
geometry.boundsTree.refit();

Serialization and Deserialization

const geometry = new KnotBufferGeometry( 1, 0.5, 40, 10 );
const bvh = new MeshBVH( geometry );
const serialized = MeshBVH.serialize( bvh );

// ...

const deserializedBVH = MeshBVH.deserialize( serialized, geometry );
geometry.boundsTree = deserializedBVH;

Asynchronous Generation

NOTE WebWorker syntax is inconsistently supported across bundlers and sometimes not supported at all so the GenerateMeshBVHWorker class is not exported from the package root. If needed the code from src/worker can be copied and modified to accomodate a particular build process.

import { GenerateMeshBVHWorker } from 'three-mesh-bvh/src/workers/GenerateMeshBVHWorker.js';

// ...

const geometry = new KnotBufferGeometry( 1, 0.5, 40, 10 );
const worker = new GenerateMeshBVHWorker();
worker.generate( geometry ).then( bvh => {

    geometry.boundsTree = bvh;

} );

BVH Queries in a Shader

See the shader implementation in the simple GPU Path Tracing example for an example on how to perform BVH ray queries in a shader. Or the GPU SDF Generation example for how to perform distance and closest point to point queries in a shader.

Exports

Split Strategy Constants

CENTER

Option for splitting each BVH node down the center of the longest axis of the bounds.

This is the fastest construction option and will yield a good, performant bounds.

AVERAGE

Option for splitting each BVH node at the average point along the longest axis for all triangle centroids in the bounds.

This strategy may be better than CENTER with some geometry.

SAH

Option to use a Surface Area Heuristic to split the bounds more optimally. This SAH implementation tests 32 discrete splits in each node along each axis to determine which split is the lowest cost.

This is the slowest construction option but will yield the best bounds of the three options and use the least memory.

Shapecast Intersection Constants

NOT_INTERSECTED

Indicates the shape did not intersect the given bounding box.

INTERSECTED

Indicates the shape did intersect the given bounding box.

CONTAINED

Indicate the shape entirely contains the given bounding box.

MeshBVH

The MeshBVH generation process modifies the geometry's index bufferAttribute in place to save memory. The BVH construction will use the geometry's boundingBox if it exists or set it if it does not. The BVH will no longer work correctly if the index buffer is modified.

Note that all query functions expect arguments in local space of the BVH and return results in local space, as well. If world space results are needed they must be transformed into world space using object.matrixWorld.

static .serialize

static serialize( bvh : MeshBVH, options : Object = null ) : SerializedBVH

Generates a representation of the complete bounds tree and the geometry index buffer which can be used to recreate a bounds tree using the deserialize function. The serialize and deserialize functions can be used to generate a MeshBVH asynchronously in a background web worker to prevent the main thread from stuttering. The BVH roots buffer stored in the serialized representation are the same as the ones used by the original BVH so they should not be modified. If SharedArrayBuffers are used then the same BVH memory can be used for multiple BVH in multiple WebWorkers.

bvh is the MeshBVH to be serialized. The options object can have the following fields:

{

	// if true then a clone of the `geometry.index.array` and MeshBVH buffers are made which slightly slower but
	// ensures modifications do not affect the serialized content. Can be set to "false" if it is guaranteed that
	// no modifications will be made, to save memory, or transfer and share them across WebWorkers if SharedArrayBuffers
	// are being used.
	cloneBuffers: true

}

static .deserialize

static deserialize( data : SerializedBVH, geometry : BufferGeometry, options : Object = null ) : MeshBVH

Returns a new MeshBVH instance from the serialized data. geometry is the geometry used to generate the original BVH data was derived from. The root buffers stored in data are set directly on the new BVH so the memory is shared.

The options object can have the following fields:

{
	// If true then the buffer for the `geometry.index` attribute is set from the serialized
	// data attribute or created if an index does not exist.
	setIndex: true,

}

NOTE: In order for the bounds tree to be used for casts the geometry index attribute must be replaced by the data in the SeralizedMeshBVH object.

.constructor

constructor( geometry : BufferGeometry, options : Object )

Constructs the bounds tree for the given geometry and produces a new index attribute buffer. A reference to the passed geometry is retained. The available options are

{
    // Which split strategy to use when constructing the BVH.
    strategy: CENTER,

    // The maximum depth to allow the tree to build to.
    // Setting this to a smaller trades raycast speed for better construction
    // time and less memory allocation.
    maxDepth: 40,

    // The number of triangles to aim for in a leaf node. Setting this to a lower
    // number can improve raycast performance but increase construction time and
    // memory footprint.
    maxLeafTris: 10,

    // If true then the bounding box for the geometry is set once the BVH
    // has been constructed.
    setBoundingBox: true,

    // If true then the MeshBVH will use SharedArrayBuffer rather than ArrayBuffer when
    // initializing the BVH buffers. Geometry index data will be created as a
    // SharedArrayBuffer only if it needs to be created. Otherwise it is used as-is.
    useSharedArrayBuffer: false,

    // An optional function that takes a "progress" argument in the range [0, 1]
    // indicating the progress along BVH generation. Useful primarily when generating
    // the BVH asynchronously with the GenerateMeshBVHWorker class.
    onProgress: null,

    // Print out warnings encountered during tree construction.
    verbose: true,

}

NOTE: The geometry's index attribute array is modified in order to build the bounds tree. If the geometry has no index then one is added.

.raycast

raycast( ray : Ray, side : FrontSide | BackSide | DoubleSide = FrontSide ) : Array<RaycastHit>

raycast( ray : Ray, material : Array<Material> | Material ) : Array<RaycastHit>

Returns all raycast triangle hits in unsorted order. It is expected that ray is in the frame of the BVH already. Likewise the returned results are also provided in the local frame of the BVH. The side identifier is used to determine the side to check when raycasting or a material with the given side field can be passed. If an array of materials is provided then it is expected that the geometry has groups and the appropriate material side is used per group.

Note that unlike three.js' Raycaster results the points and distances in the intersections returned from this function are relative to the local frame of the MeshBVH. When using the acceleratedRaycast function as an override for Mesh.raycast they are transformed into world space to be consistent with three's results.

.raycastFirst

raycastFirst( ray : Ray, side : FrontSide | BackSide | DoubleSide = FrontSide ) : RaycastHit

raycastFirst( ray : Ray, material : Array<Material> | Material ) : RaycastHit

Returns the first raycast hit in the model. This is typically much faster than returning all hits. See raycast for information on the side and material options as well as the frame of the returned intersections.

.intersectsSphere

intersectsSphere( sphere : Sphere ) : Boolean

Returns whether or not the mesh instersects the given sphere.

.intersectsBox

intersectsBox( box : Box3, boxToBvh : Matrix4 ) : Boolean

Returns whether or not the mesh intersects the given box.

The boxToBvh parameter is the transform of the box in the meshs frame.

.intersectsGeometry

intersectsGeometry( geometry : BufferGeometry, geometryToBvh : Matrix4 ) : Boolean

Returns whether or not the mesh intersects the given geometry.

The geometryToBvh parameter is the transform of the geometry in the BVH's local frame.

Performance improves considerably if the provided geometry also has a boundsTree.

.closestPointToPoint

closestPointToPoint(
	point : Vector3,
	target : Object = {},
	minThreshold : Number = 0,
	maxThreshold : Number = Infinity
) : target

Computes the closest distance from the point to the mesh and gives additional information in target. The target can be left undefined to default to a new object which is ultimately returned by the function.

If a point is found that is closer than minThreshold then the function will return that result early. Any triangles or points outside of maxThreshold are ignored. If no point is found within the min / max thresholds then null is returned and the target object is not modified.

target : {
	point : Vector3,
	distance : Number,
	faceIndex : Number
}

The returned faceIndex can be used with the standalone function getTriangleHitPointInfo to obtain more information like UV coordinates, triangle normal and materialIndex.

.closestPointToGeometry

closestPointToGeometry(
	geometry : BufferGeometry,
	geometryToBvh : Matrix4,
	target1 : Object = {},
	target2 : Object = {},
	minThreshold : Number = 0,
	maxThreshold : Number = Infinity
) : target1

Computes the closest distance from the geometry to the mesh and puts the closest point on the mesh in target1 (in the frame of the BVH) and the closest point on the other geometry in target2 (in the geometry frame). If target1 is not provided a new Object is created and returned from the function.

The geometryToBvh parameter is the transform of the geometry in the BVH's local frame.

If a point is found that is closer than minThreshold then the function will return that result early. Any triangles or points outside of maxThreshold are ignored. If no point is found within the min / max thresholds then null is returned and the target objects are not modified.

target1 and target2 are optional objects that similar to the target parameter in closestPointPoint and set with the same fields as that function.

The returned in target1 and target2 can be used with the standalone function getTriangleHitPointInfo to obtain more information like UV coordinates, triangle normal and materialIndex.

Note that this function can be very slow if geometry does not have a geometry.boundsTree computed.

.shapecast

shapecast(
	callbacks : {

		traverseBoundsOrder : (
			box: Box3
		) => Number = null,

		intersectsBounds : (
			box : Box3,
			isLeaf : Boolean,
			score : Number | undefined,
			depth : Number,
			nodeIndex : Number
		) => NOT_INTERSECTED | INTERSECTED | CONTAINED,

		intersectsRange : (
			triangleOffset : Number,
			triangleCount : Number
			contained : Boolean,
			depth : Number,
			nodeIndex : Number,
			box: Box3
		) => Boolean = null,

		intersectsTriangle : (
			triangle : ExtendedTriangle,
			triangleIndex : Number,
			contained : Boolean,
			depth : Number
		) => Boolean = null,

	}

) : Boolean

A generalized cast function that can be used to implement intersection logic for custom shapes. This is used internally for intersectsBox, intersectsSphere, and more. The function returns as soon as a triangle has been reported as intersected and returns true if a triangle has been intersected. The bounds are traversed in depth first order calling traverseBoundsOrder, intersectsBoundsFunc, intersectsRange, and intersectsTriangle for each node and using the results to determine when to end traversal. The depth value passed to callbacks indicates the depth of the bounds the provided box or triangle range belongs to unless the triangles are indicated to be CONTAINED, in which case depth is the depth of the parent bounds that were contained. The depth field can be used to precompute, cache to an array, and then read information about a parent bound to improve performance while traversing because nodes are traversed in a dpeth first order. The triangleIndex parameter specifies the index of the triangle in the index buffer. The three vertex indices can be computed as triangleIndex * 3 + 0, triangleIndex * 3 + 1, triangleIndex * 3 + 2.

traverseBoundsOrder takes as an argument the axis aligned bounding box representing an internal node local to the BVH and returns a score (often distance) used to determine whether the left or right node should be traversed first. The shape with the lowest score is traversed first.

intersectsBounds takes the axis aligned bounding box representing an internal node local to the bvh, whether or not the node is a leaf, the score calculated by traverseBoundsOrder, the node depth, and the node index (for use with the refit function) and returns a constant indicating whether or not the bounds is intersected or contained meaning traversal should continue. If CONTAINED is returned (meaning the bounds is entirely encapsulated by the shape) then an optimization is triggered allowing the range and / or triangle intersection callbacks to be run immediately rather than traversing the rest of the child bounds.

intersectsRange takes a triangle offset and count representing the number of triangles to be iterated over. 1 triangle from this range represents 3 values in the geometry's index buffer. If this function returns true then traversal is stopped and intersectsTriangle is not called if provided.

intersectsTriangle takes a triangle and the triangle index and returns whether or not the triangle has been intersected. If the triangle is reported to be intersected the traversal ends and the shapecast function completes. If multiple triangles need to be collected or intersected return false here and push results onto an array. contained is set to true if one of the parent bounds was marked as entirely contained (returned CONTAINED) in the intersectsBoundsFunc function.

.refit

refit( nodeIndices : Array<Number> | Set<Number> = null ) : void

Refit the node bounds to the current triangle positions. This is quicker than regenerating a new BVH but will not be optimal after significant changes to the vertices. nodeIndices is a set of node indices (provided by the shapecast function, see example snippet below) that need to be refit including all internal nodes. If one of a nodes children is also included in the set of node indices then only the included child bounds are traversed. If neither child index is included in the nodeIndices set, though, then it is assumed that every child below that node needs to be updated.

Here's how to get the set of indices that need to be refit:

const nodeIndices = new Set();
bvh.shapecast(

	{

		intersectsBounds: ( box, isLeaf, score, depth, nodeIndex ) => {

			if ( /* intersects shape */ ) {

				nodeIndices.add( nodeIndex );
				return INTERSECTED;

			}

			return NOT_INTERSECTED;

		},

		intersectsRange: ( offset, count, contained, depth, nodeIndex ) => {

			/* collect triangles / vertices to move */

			// the nodeIndex here will have always already been added to the set in the
			// `intersectsBounds` callback.
			nodeIndices.add( nodeIndex );

		}

	}

);

/* update the positions of the triangle vertices */

// update the BVH bounds of just the bounds that need to be updated
bvh.refit( nodeIndices );

.getBoundingBox

getBoundingBox( target : Box3 ) : Box3

Get the bounding box of the geometry computed from the root node bounds of the BVH. Significantly faster than BufferGeometry.computeBoundingBox.

SerializedBVH

.roots

roots : Array<ArrayBuffer>

.index

index : TypedArray

MeshBVHVisualizer

extends THREE.Group

Displays a view of the bounds tree up to the given depth of the tree. Update() must be called after any fields that affect visualization geometry are changed.

Note: The visualizer is expected to be a sibling of the mesh being visualized.

.depth

depth : Number

The depth to traverse and visualize the tree to.

.color

color = 0x00FF88 : THREE.Color

The color to render the bounding volume with.

.opacity

opacity = 0.3 : Number

The opacity to render the bounding volume with.

.displayParents

displayParents = false : Boolean

Whether or not to display the parent bounds.

.displayEdges

displayEdges = true : Boolean

If true displays the bounds as edges other displays the bounds as solid meshes.

.edgeMaterial

edgeMaterial : LineBasicMaterial

The material to use when rendering edges.

.meshMaterial

meshMaterial : MeshBasicMaterial

The material to use when rendering as a sold meshes.

.constructor

constructor( mesh: THREE.Mesh, depth = 10 : Number )

Instantiates the helper with a depth and mesh to visualize.

.update

update() : void

Updates the display of the bounds tree in the case that the bounds tree has changed or the depth parameter has changed.

.dispose

dispose() : void

Disposes of the material used.

ExtendedTriangle

extends THREE.Triangle

An extended version of three.js' Triangle class. A variety of derivative values are cached on the object to accelerate the intersection functions. .needsUpdate must be set to true when modifying the triangle parameters.

.needsUpdate

needsUpdate : Boolean

Indicates that the triangle fields have changed so cached variables to accelerate other function execution can be updated. Must be set to true after modifying the triangle a, b, c fields.

.intersectsTriangle

intersectsTriangle( other : Triangle, target? : Line3  ) : Boolean;

Returns whether the triangles intersect. target is set to the line segment representing the intersection.

.intersectsSphere

intersectsSphere( sphere : Sphere ) : Boolean

Returns whether the triangle intersects the given sphere.

.closestPointToSegment

closestPointToSegment( segment : Line3, target1? : Vector3, target2? : Vector3 ) : Number

Returns the distance to the provided line segment. target1 and target2 are set to the closest points on the triangle and segment respectively.

.distanceToPoint

distanceToPoint( point : Vector3 ) : Number

Returns the distance to the provided point.

.distanceToTriangle

distanceToTriangle( tri : Triangle ) : Number

Returns the distance to the provided triangle.

OrientedBox

extends THREE.Box3

An oriented version of three.js' Box3 class. A variety of derivative values are cached on the object to accelerate the intersection functions. .needsUpdate must be set to true when modifying the box parameters.

.matrix

matrix : Matrix4

Matrix transformation applied to the box.

.needsUpdate

updateUpdate : Boolean

Indicates that the bounding box fields have changed so cached variables to accelerate other function execution can be updated. Must be set to true after modifying the oriented box min, max, matrix fields.

.set

set( min : Vector3, max : Vector3, matrix : Matrix4 ) : this

Sets the oriented box parameters.

.intersectsBox

intersectsBox( box : Box3 ) : Boolean

Returns true if intersecting with the provided box.

.intersectsTriangle

intersectsTriangle( tri : Triangle ) : Boolean

Returns true if intersecting with the provided triangle.

.closestPointToPoint

closestPointToPoint( point : Vector3, target = null : Vector3 ) : Number

Returns the distance to the provided point. Sets target to the closest point on the surface of the box if provided.

.distanceToPoint

distanceToPoint( point : Vector3 ) : Number

Returns the distance to the provided point.

.distanceToBox

distanceToBox( box : Box3, threshold = 0 : Number, target1 = null : Vector3, target2 = null : Vector3 ) : Number

Returns the distance to the provided box. threshold is an optional distance to return early if the distance is found to be within it. target1 and target2 are set to the points on the surface of this box and the box argument respectively.

Extensions

Raycaster.firstHitOnly

firstHitOnly = false : Boolean

If the Raycaster member firstHitOnly is set to true then the .acceleratedRaycast function will call the .raycastFirst function to retrieve hits which is generally faster.

.computeBoundsTree

computeBoundsTree( options : Object ) : void

A pre-made BufferGeometry extension function that builds a new BVH, assigns it to boundsTree, and applies the new index buffer to the geometry. Comparable to computeBoundingBox and computeBoundingSphere.

THREE.BufferGeometry.prototype.computeBoundsTree = computeBoundsTree;

.disposeBoundsTree

disposeBoundsTree() : void

A BufferGeometry extension function that disposes of the BVH.

THREE.BufferGeometry.prototype.disposeBoundsTree = disposeBoundsTree;

.acceleratedRaycast

acceleratedRaycast( ... )

An accelerated raycast function with the same signature as THREE.Mesh.raycast. Uses the BVH for raycasting if it's available otherwise it falls back to the built-in approach. The results of the function are designed to be identical to the results of the conventional THREE.Mesh.raycast results.

If the raycaster object being used has a property firstHitOnly set to true, then the raycasting will terminate as soon as it finds the closest intersection to the ray's origin and return only that intersection. This is typically several times faster than searching for all intersections.

THREE.Mesh.prototype.raycast = acceleratedRaycast;

StaticGeometryGenerator

A utility class for taking a set of SkinnedMeshes or morph target geometry and baking it into a single, static geometry that a BVH can be generated for.

.useGroups

useGroups = true : Boolean

If true then groups are used to support an array of materials on the mesh.

.attributes

attributes = [ 'position', 'normal', 'tangent', 'uv', 'uv2' ] : Array<String>

The set of attributes to copy onto the static geometry.

.applyWorldTransforms

applyWorldTransforms = true : Boolean

Whether to transform the vertices of the geometry by the world transforms of each mesh when generating.

constructor

constructor( object : Array<Object3D> )

Takes an array of object hierarchies to bake into a single static geometry.

.getMaterials

getMaterials() : Array<Material>

Returns an array of materials for the meshes to be merged. These can be used alongside the generated geometry when creating a mesh: new Mesh( geometry, generator.getMaterials() ).

.generate

generate( target = new BufferGeometry() : BufferGeometry ) : BufferGeometry

Generates a single, static geometry for the passes meshes. When generating for the first time an empty target geometry is expected. The same generated geometry can be passed into the function on subsequent calls to update the geometry in place to save memory. An error will be thrown if the attributes or geometry on the meshes to bake has been changed and are incompatible lengths, types, etc.

On subsequent calls the "index" buffer will not be modified so any BVH generated for the geometry is unaffected. Once the geometry is updated the MeshBVH.refit function can be called to update the BVH.

GenerateMeshBVHWorker

Helper class for generating a MeshBVH for a given geometry in asynchronously in a worker. The geometry position and index buffer attribute ArrayBuffers are transferred to the Worker while the BVH is being generated meaning the geometry will be unavailable to use while the BVH is being processed unless SharedArrayBuffers are used. They will be automatically replaced when the MeshBVH is finished generating.

NOTE It's best to reuse a single instance of this class to avoid the overhead of instantiating a new Worker.

See note in Asyncronous Generation use snippet.

.running

running : Boolean;

Flag indicating whether or not a BVH is already being generated in the worker.

.generate

generate( geometry : BufferGeometry, options : Object ) : Promise< MeshBVH >;

Generates a MeshBVH instance for the given geometry with the given options in a WebWorker. Returns a promise that resolves with the generated MeshBVH. This function will throw an error if it is already running.

.dispose

dispose() : void;

Terminates the worker.

Debug Functions

estimateMemoryInBytes

estimateMemoryInBytes( bvh : MeshBVH ) : Number

Roughly estimates the amount of memory in bytes a BVH is using.

getBVHExtremes

getBVHExtremes( bvh : MeshBVH ) : Array< Object >

Measures the min and max extremes of the tree including node depth, leaf triangle count, and number of splits on different axes to show how well a tree is structured. Returns an array of extremes for each group root for the bvh. The objects are structured like so:

{
	// The total number of nodes in the tree including leaf nodes.
	nodeCount: Number,

	// The total number of leaf nodes in the tree.
	leafNodeCount: Number,

	// A total tree score based on the surface area heuristic score
	// useful for comparing the quality and performance capability
	// of the bounds tree. Lower score is better and based on the surface
	// area of bounds and how many triangles are stored within.
	surfaceAreaScore: Number,

	// The min and max of leaf nodes in the tree.
	depth: { min: Number, max: Number },

	// The min and max number of triangles contained within the
	// bounds the leaf nodes.
	tris: { min: Number, max: Number },

	// The number of splits on any given axis.
	splits: [ Number, Number, Number ]
}

NOTE The when using the refit function the surfaceAreaScore can be used to check how significantly the structure of the BVH has degraded and rebuild it if it has changed beyond some threshold ratio.

Individual Functions

Functions exported individually not part of a class.

getTriangleHitPointInfo

getTriangleHitPointInfo(
	point: Vector3,
	geometry : BufferGeometry,
	triangleIndex: Number
	target: Object
) : Object

This function returns information of a point related to a geometry. It returns the target object or a new one if passed undefined:

target : {
	face: {
		a: Number,
		b: Number,
		c: Number,
		materialIndex: Number,
		normal: Vector3
	},
	uv: Vector2
}

• a, b, c: Triangle indices
• materialIndex: Face material index or 0 if not available.
• normal: Face normal
• uv: UV coordinates.

This function can be used after a call to closestPointPoint or closestPointToGeometry to retrieve more detailed result information.

Shader and Texture Packing API

In addition to queries in Javascript the BVH can be packed into a series of textures so raycast queries can be performed in a shader using provided WebGL shader functions. See the shader implementation in the simple GPU Path Tracing example for an example on how to use the functionality.

*VertexAttributeTexture

FloatVertexAttributeTexture

UIntVertexAttributeTexture

IntVertexAttributeTexture

extends THREE.DataTexture

Float, Uint, and Int VertexAttributeTexture implementations are designed to simplify the efficient packing of a three.js BufferAttribute into a texture. An instance can be treated as a texture and when passing as a uniform to a shader they should be used as a sampler2d, usampler2d, and isampler2d when using the Float, Uint, and Int texture types respectively.

.overrideItemSize

overrideItemSize : Number = null

Treats BufferAttribute.itemSize as though it were set to this value when packing the buffer attribute texture. Throws an error if the value does not divide evenly into the length of the BufferAttribute buffer (count * itemSize % overrideItemSize).

Specifically used to pack geometry indices into an RGB texture rather than an Red texture.

.updateFrom

updateFrom( attribute : THREE.BufferAttribute ) : void

Updates the texture to have the data contained in the passed BufferAttribute using the BufferAttribute itemSize field, normalized field, and TypedArray layout to determine the appropriate texture layout, format, and type. The texture dimensions will always be square. Because these are intended to be sampled as 1D arrays the width of the texture msut be taken into account to derive a sampling uv. See texelFetch1D in shaderFunctions.

MeshBVHUniformStruct

A shader uniform object corresponding to the BVH shader struct defined in shaderStructs. The object contains four textures containing information about the BVH and geometry so it can be queried in a shader using the bvh intersection functions defined in shaderFunctions. This object is intended to be used as a shader uniform and read in the shader as a BVH struct.

.updateFrom

updateFrom( bvh : MeshBVH ) : void

Updates the object and associated textures with data from the provided BVH.

.dispose

dispose() : void

Dispose of the associated textures.

Shader Function and Struct Exports

shaderStructs

shaderStructs : string

Set of shaders structs and defined constants used for interacting with the packed BVH in a shader. See src/gpu/shaderFunctions.js for full implementations and declarations.

shaderFunctions

shaderFunctions : string

Set of shader functions used for interacting with the packed BVH in a shader and sampling VertexAttributeTextures. See src/gpu/shaderFunctions.js for full implementations and declarations.

Gotchas

• When querying the MeshBVH directly all shapes and geometry are expected to be specified in the local frame of the BVH. When using three.js' built in raycasting system all results are implicitly transformed into world coordinates.
• A bounds tree can be generated for either an indexed or non-indexed BufferGeometry, but an index will be produced and retained as a side effect of the construction.
• The bounds hierarchy is not dynamic, so geometry that uses morph targets or skinning cannot be used. Though if vertex positions are modified directly the refit function can be used to adjust the bounds tree.
• If the geometry is changed then a new bounds tree will need to be generated or refit.
• InterleavedBufferAttributes are not supported with the geometry index buffer attribute.
• A separate bounds tree is generated for each geometry group, which could result in less than optimal raycast performance on geometry with lots of groups.
• Due to errors related to floating point precision it is recommended that geometry be centered using BufferGeometry.center() before creating the BVH if the geometry is sufficiently large or off center so bounds tightly contain the geometry as much as possible.

Running Examples Locally

To run the examples locally:

• Run npm start
• Then visit localhost:9080/example/dev-bundle/<demo-name>.html

Where <demo-name> is the name of the HTML file from example folder.

Used and Supported by

...and more!

Changelog

[0.5.19] - 2022-11-28

Fixed

• StaticGeometryGenerator: now correctly only traverses and includes visible meshes.