Kyle Decot - 6 months ago 43

iOS Question

I'm currently using the following to get the total height of all of the child nodes in a

`SCNNode`

`CGFloat(columnNode.childNodes.reduce(CGFloat()) {`

let geometry = $1.geometry! as SCNBox

return $0 + geometry.height

})

Answer

Yes, and a way that'll get you a more correct answer, too. Summing the height of all the child nodes' geometries...

- only works if the geometry is an
`SCNBox`

- doesn't account for the child nodes' transforms (what if they're moved, rotated or scaled?)
- doesn't account for the parent node's transform (what if you want height in scene space?)

What you want is the `SCNBoundingVolume`

protocol, which applies to all nodes and geometries, and describes the smallest rectangular or spherical space containing all of a node's (and its subnodes') content.

In Swift 3, this is super easy:

```
let (min, max) = columnNode.boundingBox
```

After this, `min`

and `max`

are the coordinates of the lower-rear-left and upper-front-right corners of the smallest possible box containing everything inside `columnNode`

, no matter how that content is arranged (and what kind of geometry is involved). These coordinates are expressed in the same system as `columnNode.position`

, so if the "height" you're looking for is in the y-axis direction of that space, just subtract the y-coordinates of those two vectors:

```
let height = max.y - min.y
```

In Swift 2, the syntax for it is a little weird, but it works well enough:

```
var min = SCNVector3Zero
var max = SCNVector3Zero
columnNode.getBoundingBoxMin(&min, max: &max)
```