gkjohnson / Three Mesh Bvh
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three-mesh-bvh
A BVH implementation to speed up raycasting against and enable intersection tests for three.js meshes.
Casting 500 rays against an 80,000 polygon model at 60fps!
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, { lazyGeneration: false } );
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( mesh, raycaster, raycaster.ray );
// spherecasting
// ensure the sphere is in the lcoal space of hte geometry being cast against
sphere.applyMatrix4( invMat );
const intersects = bvh.intersectsSphere( mesh, sphere );
Serialization and Deserialization
const geometry = new KnotBufferGeometry( 1, 0.5, 40, 10 );
const bvh = new MeshBVH( geometry );
const serialized = MeshBVH.serialize( bvh, geometry );
// ...
const deserializedBVH = MeshBVH.deserialize( serialized, geometry );
geometry.boundsTree = deserializedBVH;
Asynchronous Generation
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;
} );
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 but will yield a less optimal hierarchy.
AVERAGE
Option for splitting each BVH node at the average point along the longest axis for all triangle centroids in the bounds.
SAH
Option to use a Surface Area Heuristic to split the bounds optimally.
This is the slowest construction option.
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.
static .serialize
static serialize( bvh : MeshBVH, geometry : BufferGeometry, copyIndexBuffer = true : Boolean ) : 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.
bvh
is the MeshBVH to be serialized and geometry
is the bufferGeometry used to generate and raycast against using the bvh
.
If copyIndexBuffer
is true then a copy of the geometry.index.array
is made which is slower but useful is the geometry index is intended to be modified.
static .deserialize
static deserialize( data : SerializedBVH, geometry : BufferGeometry, setIndex = true : Boolean ) : MeshBVH
Returns a new MeshBVH instance from the serialized data. geometry
is the geometry used to generate the original bvh data
was derived from. If setIndex
is true then the buffer for the geometry.index
attribute is set from the serialized data attribute or created if an index does not exist.
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.
NOTE: The returned MeshBVH is a fully generated, buffer packed BVH instance to improve memory footprint and uses the same buffers passed in on the data.root
property.
.constructor
constructor( geometry : BufferGeometry, options : Object )
Constructs the bounds tree for the given geometry and produces a new index attribute buffer. 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.
maxLeafTris: 10,
// Print out warnings encountered during tree construction.
verbose: true,
// If true the bounds tree is generated progressively as the tree is used allowing
// for a fast initialization time and memory allocation as needed but a higher memory
// footprint once the tree is completed. The initial raycasts are also slower until the
// tree is built up.
// If false then the bounds tree will be completely generated up front and packed into
// an array buffer for a lower final memory footprint and long initialization time.
// Note that this will keep intermediate buffers needed for generation in scope until
// the tree has been fully generated.
lazyGeneration: 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( mesh : Mesh, raycaster : Raycaster, ray : Ray, intersects : Array ) : Array<RaycastHit>
Adds all raycast triangle hits in unsorted order to the intersects
array. It is expected that ray
is in the frame of the mesh being raycast against and that the geometry on mesh
is the same as the one used to generate the bvh.
.raycastFirst
raycastFirst( mesh : Mesh, raycaster : Raycaster, ray : Ray ) : RaycastHit
Returns the first raycast hit in the model. This is typically much faster than returning all hits.
.intersectsSphere
intersectsSphere( mesh : Mesh, sphere : Sphere ) : Boolean
Returns whether or not the mesh instersects the given sphere.
.intersectsBox
intersectsBox( mesh : Mesh, 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( mesh : Mesh, 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 mesh's frame.
Performance improves considerably if the provided geometry also has a boundsTree
.
.closestPointToPoint
closestPointToPoint(
mesh : Mesh,
point : Vector3,
target : Vector3,
minThreshold : Number = 0,
maxThreshold : Number = Infinity
) : Number
Returns the closest distance from the point to the mesh and puts the closest point on the mesh in target
.
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.
.closestPointToGeometry
closestPointToGeometry(
mesh : Mesh,
geometry : BufferGeometry,
geometryToBvh : Matrix4,
target1 : Vector3 = null,
target2 : Vector3 = null,
minThreshold : Number = 0,
maxThreshold : Number = Infinity
) : Number
Returns the closest distance from the geometry to the mesh and puts the closest point on the mesh in target1
and the closest point on the other geometry in target2
in the frame of the BVH.
The geometryToBvh
parameter is the transform of the geometry in the mesh's 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.
.shapecast
shapecast(
mesh : Mesh,
intersectsBoundsFunc : (
box : Box3,
isLeaf : Boolean,
score : Number | undefined,
depth : Number
) => NOT_INTERSECTED | INTERSECTED | CONTAINED,
intersectsTriangleFunc : (
triangle : Triangle,
index1 : Number,
index2 : Number,
index3 : Number,
contained : Boolean,
depth : Number
) => Boolean = null,
orderNodesFunc : (
box: Box3
) => Number = null
) : Boolean
A generalized cast function that can be used to implement intersection logic for custom shapes. This is used internally for intersectsBox and intersectsSphere. 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 orderNodesFunc
, intersectsBoundsFunc
and intersectsTrianglesFunc
for each node and using the results to determine traversal depth. The depth
value passed to intersectsBoundsFunc
and intersectsTriangleFunc
indicates the depth of the bounds the provided box or bounds belongs to unless the triangles are indicated to be CONTAINED
, in which case depth is the depth of the parent bounds that were contained. It can be used to precompute, cache, and then read information about a parent bound to improve performance while traversing.
mesh
is the is the object this BVH is representing.
intersectsBoundsFunc
takes the axis aligned bounding box representing an internal node local to the bvh, whether or not the node is a leaf, and the score calculated by orderNodesFunc
and returns a constant indicating whether or not the bounds is intersected or contained and traversal should continue. If CONTAINED
is returned then and optimization is triggered allowing all child triangles to be checked immediately rather than traversing the rest of the child bounds.
intersectsTriangleFunc
takes a triangle and the vertex indices used by the triangle from the geometry and returns whether or not the triangle has been intersected with. 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 in the intersectsBoundsFunc
function.
orderNodesFunc
takes the axis aligned bounding box representing an internal node local to the bvh and returns a score or distance representing the distance to the shape being intersected with. The shape with the lowest score is traversed first.
SerializedBVH
.roots
roots : Array< ArrayBuffer >
.index
index : TypedArray
MeshBVHVisualizer
Displays a view of the bounds tree up to the given depth of the tree.
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.
.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.
Extensions
Raycaster.firstHitOnly
firstHitOnly = false : Boolean
The 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.
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;
GenerateMeshBVHWorker
Class for generating a MeshBVH asynchronously in a WebWorker to avoid it blocking the main thread. The class is not exported via index.js because they require extra effort to integrate with some build processes due to Worker sytax being inconsistently supported. UMD variants of these functions are not provided. The class must be imported from the src/workers/GenerateMeshWorker.js
file.
.generate
generate( geometry : BufferGeometry, options : Object ) : Promise<MeshBVH>
Generates a BVH for the given geometry in a WebWorker so it can be created asynchronously. A Promise is returned that resolves with the generated BVH. During the generation the geometry.attributes.position
array and geometry.index
array (if it exists) are transferred to the worker so the geometry will not be usable until the BVH generation is complete and the arrays are transferred back.
.terminate
terminate() : void
Disposes of the web 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:
{
depth: { min: Number, max: Number },
tris: { min: Number, max: Number },
splits: [ Number, Number, Number ]
}
Gotchas
- This is intended to be used with complicated, high-poly meshes. With less complex meshes, the benefits are negligible.
- 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 cannot be used.
- If the geometry is changed then a new bounds tree will need to be generated.
- Only BufferGeometry (not Geometry) is supported when building a bounds tree.
- InterleavedBufferAttributes are not supported on the geometry index or position attributes.
- A separate bounds tree is generated for each geometry group, which could result in poorer 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. - Geometry with a lot of particularly long triangles on one axis can lead to a less than optimal bounds tree (see #121).