Threejs Object3D.raycast source code

casamigos17 · July 10, 2024, 5:07pm

Hi there, I wonder how threejs raycast is returning the face intersect on raycast intersect objects. However, when diving into the git repo, I came up with the surprise that the code source for that method is not posted in github:

github.com

mrdoob/three.js/blob/1845f6cd0525b5c73b9da33c40e198c360af29f1/src/core/Object3D.js#L532


      
          	getWorldDirection( target ) {
          
          		this.updateWorldMatrix( true, false );
          
          		const e = this.matrixWorld.elements;
          
          		return target.set( e[ 8 ], e[ 9 ], e[ 10 ] ).normalize();
          
          	}
          
          	raycast( /* raycaster, intersects */ ) {}
          
          	traverse( callback ) {
          
          		callback( this );
          
          		const children = this.children;
          
          		for ( let i = 0, l = children.length; i < l; i ++ ) {
          
          			children[ i ].traverse( callback );

Is there anywhere I can see the original source code. By the way, I’m working on a code to get faces from a mesh.

manthrax · July 10, 2024, 5:16pm

Different object types implement that method. It gets overriden by object type I think… so you want to look at Mesh probably.

edit: three.js/src/objects/Mesh.js at e14d2b13903e18c39edb6e738367e69facadc7e2 · mrdoob/three.js · GitHub

and

github.com

mrdoob/three.js/blob/e14d2b13903e18c39edb6e738367e69facadc7e2/src/objects/Mesh.js#L196


      
          			if ( _ray.intersectsBox( geometry.boundingBox ) === false ) return;
          
          		}
          
          		// test for intersections with geometry
          
          		this._computeIntersections( raycaster, intersects, _ray );
          
          	}
          
          	_computeIntersections( raycaster, intersects, rayLocalSpace ) {
          
          		let intersection;
          
          		const geometry = this.geometry;
          		const material = this.material;
          
          		const index = geometry.index;
          		const position = geometry.attributes.position;
          		const uv = geometry.attributes.uv;
          		const uv1 = geometry.attributes.uv1;

casamigos17 · July 10, 2024, 5:22pm

Thanks for your prompt reply manthrax!

manthrax · July 10, 2024, 5:22pm

you’re welcome. hope it helps.

casamigos17 · July 10, 2024, 5:42pm

It’s weird that they are using the X coordinates
[three.js/src/objects/Mesh.js at e14d2b13903e18c39edb6e738367e69facadc7e2 · mrdoob/three.js · GitHub]

of vertices as the index in Mesh.getVertexPosition(a, _vA )
[three.js/src/objects/Mesh.js at e14d2b13903e18c39edb6e738367e69facadc7e2 · mrdoob/three.js · GitHub]

manthrax · July 10, 2024, 5:49pm

Yup. It does look weird But I think its just a hack.

The bufferGeometry type has accessors for values out of them…
but it doesn’t have an accessor for getting just a single value out…

And an index buffer is just an array of 3 indices per triangle…
with a stride of 1 i guess…

so using .getX like that is equivalent to saying
a=index.array[j]
b=index.array[j+1]
c=index.array[j+2]

It’s ugly but I guess it works… and if that accessor is in the hot code path, it saves a few bytes of js code and might be faster than spelling out the logic… i dunno.

i.e. so as to your question… it’s not using vertices. it’s grabbing vertex indices from the index buffer.

casamigos17 · July 10, 2024, 5:52pm

Well I was not believing that until now,
thanks for clarifications manthrax!

casamigos17 · July 10, 2024, 10:14pm

Hi @manthrax
sorry to bother you again
Do you mind taking a look a this other post. It’s related to this issue and it has info about what I was trying to achieve. Unfortunately, I’m blocked.

All the best!

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Threejs Object3D.raycast source code

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