API
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Checks When a Point is Inside a Mesh

Check When a Point is Inside a Mesh

How To Check When a Point Is Inside a Mesh

This mesh method takes a Vector3 point and checks whether it is inside the mesh.

Design Outline

  1. Check whether the point is inside or outside the bounding box; if it is inside, continue with the following checks;
  2. Cast a ray from the point in the positive and negative x directions;
  3. When there is a hit, move forward from the hit point by a very small amount along the ray direction and recast the ray from the new point;
  4. Count the hits: if there are zero hits or an odd number of hits, the point is inside the mesh; if there is a nonzero even number of hits, the point is outside the mesh.

Design Method

  1. Check bounding box;
var boundInfo = this.getBoundingInfo();
var max = boundInfo.maximum;
var min = boundInfo.minimum;
if(point.x < min.x || point.x > max.x) {
	return false;
}
if(point.y < min.y || point.y > max.y) {
	return false;
}
if(point.z < min.z || point.z > max.z) {
	return false;
}
  1. Use the diameter of the mesh's bounding sphere as the distance to cast the ray.
import { Ray } from "@babylonjs/core/Culling/ray.core";
var diameter = 2 * boundInfo.boundingSphere.radius;
ray = new Ray(point, direction, diameter);
  1. Set the hit count to zero; while hits occur, increment the hit count.
var hitCount = 0;
var pickInfo = ray.intersectsMesh(this);
while (pickInfo.hit) {	
	hitCount++;
	pickInfo.pickedPoint.addToRef(direction.scale(0.00000001), point); //move point a small amout in ray direction
	ray.origin  = point;
	pickInfo = ray.intersectsMesh(this);
}
  1. Count the hits.
if((hitCount % 2) === 1) {
	var pointFound = true;
}
else if ((hitCount % 2) === 0 && hitCount > 0) {
	var pointFound = true;
}


return pointFound;

The Whole Function

Returns true if the point is inside the mesh, and false otherwise.

import { Ray } from "@babylonjs/core/Culling/ray.core";
import { Axis } from "@babylonjs/core/Maths/math.axis";
import { Vector3 } from "@babylonjs/core/Maths/math.vector";
import { Mesh } from "@babylonjs/core/Meshes/mesh";
Mesh.prototype.pointIsInside = function (point) {
    var boundInfo = this.getBoundingInfo();
    var max = boundInfo.maximum;
    var min = boundInfo.minimum;
    var diameter = 2 * boundInfo.boundingSphere.radius;
    if (point.x < min.x || point.x > max.x) {
        return false;
    }
    if (point.y < min.y || point.y > max.y) {
        return false;
    }
    if (point.z < min.z || point.z > max.z) {
        return false;
    }
    var pointFound = false;
    var d = 0;
    var hitCount = 0;
    var gap = 0;
    var distance = 0;
    var ray = new Ray(Vector3.Zero(), Axis.X, diameter);
    ;
    var pickInfo;
    var direction = point.clone();
    var refPoint = point.clone();
    hitCount = 0;
    ray.origin = refPoint;
    ray.direction = direction;
    ray.distance = diameter;
    pickInfo = ray.intersectsMesh(this);
    while (pickInfo.hit) {
        hitCount++;
        pickInfo.pickedPoint.addToRef(direction.scale(0.00000001), refPoint);
        ray.origin = refPoint;
        pickInfo = ray.intersectsMesh(this);
    }
    if ((hitCount % 2) === 1) {
        pointFound = true;
    }
    return pointFound;
};

Playground Example

Generate random points in a volume around a twelve-pointed star mesh. Place a sphere at each point and turn it red when it is inside the star.

Twelve Pointed Star

Further reading

Draw Points on a Mesh Surface
Helpful code snippet for drawing points on a mesh surface in Babylon.js.
Draw Points on a Mesh Surface
Create Points Inside A Mesh
Helpful code snippet for creating points inside a mesh in Babylon.js.
Create Points Inside A Mesh