# Check When a Point is Inside a Mesh

> Helpful code snippet for checking when a point is inside a mesh in Babylon.js.

Source: https://doc.babylonjs.com/toolsAndResources/utilities/IsInside

## 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;

```javascript
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;
}
```

2. Use the diameter of the mesh's bounding sphere as the distance to cast the ray.

```javascript
var diameter = 2 * boundInfo.boundingSphere.radius;
ray = new BABYLON.Ray(point, direction, diameter);
```

3. Set the hit count to zero; while hits occur, increment the hit count.

```javascript
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);
}
```

4. Count the hits.

```javascript
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.

```javascript
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 it is inside the star.

- [Playground: Twelve Pointed Star](https://playground.babylonjs.com/#XJEG9A#4)

## Further reading

- [How To Create Points on a Mesh Surface](https://doc.babylonjs.com/toolsAndResources/utilities/SurfaceMeshPoints)
- [How To Create Points Inside a Mesh](https://doc.babylonjs.com/toolsAndResources/utilities/InnerMeshPoints)