Convert GLKMatrix4 and CATransform3D

Question

Is there a way to cast from CATransform3D to GLKMatrix4, or do I always need to manually convert them from value to value? I guess casting would be faster.

Answer 1

Something like this should work:

CATransform3D t;
GLKMatrix4 t2 = *((GLKMatrix4 *)&t);
t = *((CATransform3D *)&t2);

Assuming CATransform3d and GLKMatrix4 have the same column/row setup. (I think so)

Answer 2

Unfortunately there is not as of now. There's most likely a hidden API call that Apple uses to convert via CALayers and OpenGL, but for now the following is your best bet. I would just make a utility class that would contain this in it.

    - (GLKMatrix4)matrixFrom3DTransformation:(CATransform3D)transform
{
    GLKMatrix4 matrix = GLKMatrix4Make(transform.m11, transform.m12, transform.m13, transform.m14,
                                       transform.m21, transform.m22, transform.m23, transform.m24,
                                       transform.m31, transform.m32, transform.m33, transform.m34,
                                       transform.m41, transform.m42, transform.m43, transform.m44);

    return matrix;
}

Using something like

CALayer *layer = [CALayer layer];
CATransform3D transform = layer.transform;
GLKMatrix4 matrix4 = *(GLKMatrix4 *)&transform;

Is called type punning. Unless you understand how this works, you should not use it. You cannot type pun a CATransform3D to a GLKMatrix4 as their data structures are different in memory.

reference link: type punning

GLKMatrix4

union _GLKMatrix4
   {
      struct
      {
      float m00, m01, m02, m03;
      float m10, m11, m12, m13;
      float m20, m21, m22, m23;
      float m30, m31, m32, m33;
};
   float m[16];
}
typedef union _GLKMatrix4 GLKMatrix4;

CATransform3D

struct CATransform3D
{
CGFloat m11, m12, m13, m14;
CGFloat m21, m22, m23, m24;
CGFloat m31, m32, m33, m34;
CGFloat m41, m42, m43, m44;
};
typedef struct CATransform3D CATransform3D;