Check When a Point is Inside a Mesh
How To Check When Point is Inside a Mesh
This mesh method takes a Vector3 point and checks if it inside the mesh.
Design Outline
- Check if point inside or outside of bounding box, when inside continue with following checks;
- Cast a ray from the point in the positive and negative x directions;
- When there is a hit, move forward from hit point a very small amount along ray direction and recast ray from new point;
- Count hits, when zero or an odd number of hits then point is inside mesh and for a even number of hits > 0 non zero then point is outside of mesh.
Design Method
- 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;}
- Use the diameter of the mesh's bounding sphere as the distance to cast the ray
var diameter = 2 * boundInfo.boundingSphere.radius;ray = new BABYLON.Ray(point, direction, diameter);
- Set hit count to zero, while hits occurring increment 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 directionray.origin = point;pickInfo = ray.intersectsMesh(this);}
- Count 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 point is inside mesh, false otherwise.
BABYLON.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 BABYLON.Ray(BABYLON.Vector3.Zero(), BABYLON.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 inside the star.
Twelve Pointed Star