SceneKit : Apply transformation on vertices

Question

I need to apply a transformation to all my vertices contained on a SCNNode . Each SCNNode contains a SCNMatrix4 transform property. I got also all vertices of my SCNNode .

 Vertex *currentVertex = [self.vectrices objectAtIndex:buff[index]];
 SCNNode *currentChildren = myNode;    
 Vertex *new = [Vertex new];

 new.x = (currentChildren.transform.m11 * currentVertex.x) + (currentChildren.transform.m12 * currentVertex.y) + (currentChildren.transform.m13 * currentVertex.z);
 new.y = (currentChildren.transform.m21 * currentVertex.x) + (currentChildren.transform.m22 * currentVertex.y) + (currentChildren.transform.m23 * currentVertex.z);
 new.z = (currentChildren.transform.m31 * currentVertex.x) + (currentChildren.transform.m32 * currentVertex.y) + (currentChildren.transform.m33 * currentVertex.z);

I got a strange resultant with wrong rotation and translation. My calcul, is it correct ?

Answer 1

SCNMatrix4 is a 4x4 matrix, but here you're using it as 3x3 matrix. You're basically removing all translations and just keeping rotations and scale factors. Take a look at SCNMatrix4ToMat4 and SCNVector4ToFloat4 (take w=1 ) and use SIMD to perform your transformations.