How to get values from simd_float4 in objective-c - objective-c

Question

I got a simd_float4*4 matrix from ARKit. I want to check the values of the matrix but found myself do not know how to do it in Objective-C. In Swift, this can be written as matrix.columns.3 to fetch a vector of values. But I do not know how to do it in Objective-C. Could someone point me a direction please. Thanks!

Answer 1

simd_float4x4 is a struct (like 4 simd_float4), and you can use
simd_float4x4.columns[index]
to access column in matrix.
/*! #abstract A matrix with 4 rows and 4 columns.*/
struct simd_float4x4 {
public var columns: (simd_float4, simd_float4, simd_float4, simd_float4)
public init()
public init(columns: (simd_float4, simd_float4, simd_float4, simd_float4))
}
Apple document link: https://developer.apple.com/documentation/simd/simd_float4x4?language=objc
hope helpful!

Answer 2

here's an example -- from this project, a pretty nice reference for Obj-C ARKit adventures -- https://github.com/markdaws/arkit-by-example/blob/part3/arkit-by-example/ViewController.m
- (void)insertGeometry:(ARHitTestResult *)hitResult {
// Right now we just insert a simple cube, later we will improve these to be more
// interesting and have better texture and shading
float dimension = 0.1;
SCNBox *cube = [SCNBox boxWithWidth:dimension height:dimension length:dimension chamferRadius:0];
SCNNode *node = [SCNNode nodeWithGeometry:cube];
// The physicsBody tells SceneKit this geometry should be manipulated by the physics engine
node.physicsBody = [SCNPhysicsBody bodyWithType:SCNPhysicsBodyTypeDynamic shape:nil];
node.physicsBody.mass = 2.0;
node.physicsBody.categoryBitMask = CollisionCategoryCube;
// We insert the geometry slightly above the point the user tapped, so that it drops onto the plane
// using the physics engine
float insertionYOffset = 0.5;
node.position = SCNVector3Make(
hitResult.worldTransform.columns[3].x,
hitResult.worldTransform.columns[3].y + insertionYOffset,
hitResult.worldTransform.columns[3].z
);
[self.sceneView.scene.rootNode addChildNode:node];
[self.boxes addObject:node];
}