What does the “simd” prefix mean in SceneKit?

Question

There is a SCNNode category named SCNNode(SIMD), which declares some properties like simdPosition, simdRotation and so on

Answer 1

SIMD is a small library built on top of vector types that you can import from . It allows for more expressive and more performant code.

For instance using SIMD you can write

simd_float3 result = a + 2.0 * b;

instead of

SCNVector3 result = SCNVector3Make(a.x + 2.0 * b.x, a.y + 2.0 * b.y, a.z + 2.0 * b.z);

In Objective-C you can not overload methods. That is you can not have both

@property(nonatomic) SCNVector3 position;
@property(nonatomic) simd_float3 position API_AVAILABLE(macos(10.13), ios(11.0), tvos(11.0), watchos(4.0));

The new SIMD-based API needed a different name, and that's why SceneKit exposes simdPosition.