Three.js - How do I determine intersections between a Mesh and a Particle System?

Question

I have a particle system using sprites which is an Object3D similar to the "interactive / points" example from three.js and a basic sphere mesh which follows my cursor.

https://threejs.org/examples/?q=point#webgl_interactive_points

What's the best way to determine when two of these objects intersect? I want to be able to push the particles with the sphere, but first I need an array of the points which are "inside the sphere". Thanks!

I know there's isPointInPath for 2d canvas. Not finding something similar for 3d, but just wanted to share. — Raphael Rafatpanah
Sphere has center and radius, you can check the condidtion if the distance from a point to the sphere's center is less than sphere's radius, then the point is inside the sphere. — prisoner849

YGilk1 YGilk1 · Accepted Answer · 2020-04-28T13:09:35

To know if a point is inside or outside the sphere, you can cast a ray from the point in a given direction. Then count the ray intesection with the sphere geometry's triangles. If the count is odd, the point is inside, else it's outside.

Some demo showing particles injection into a mesh is available here (same principle) https://github.com/heroncendre/Volpar

Three.js - How do I determine intersections between a Mesh and a Particle System?

1 Answers