How to implement in jna a structure sizeof() with an union type

Question

I updated the jvm openvr binding to the last openvr version, 1.0.5, but I am unsure about one thing.

In cpp, there is the IVROverlay class with this virtual SetOverlayIntersectionMask function:

virtual EVROverlayError SetOverlayIntersectionMask(
             VROverlayHandle_t ulOverlayHandle, 
             VROverlayIntersectionMaskPrimitive_t *pMaskPrimitives, 
             uint32_t unNumMaskPrimitives, 
             uint32_t unPrimitiveSize = sizeof( VROverlayIntersectionMaskPrimitive_t ) ) = 0;

My doubts regards the last argument.

VROverlayIntersectionMaskPrimitive_t:

struct VROverlayIntersectionMaskPrimitive_t
{
    EVROverlayIntersectionMaskPrimitiveType m_nPrimitiveType;
    VROverlayIntersectionMaskPrimitive_Data_t m_Primitive;
};

is a struct with a enum type and an union type variable, called VROverlayIntersectionMaskPrimitive_Data_t:

typedef union
{
    IntersectionMaskRectangle_t m_Rectangle;
    IntersectionMaskCircle_t m_Circle;
} VROverlayIntersectionMaskPrimitive_Data_t;

Which is being implemented by the two classes right above, IntersectionMaskRectangle_t and IntersectionMaskCircle_t

Now, the enum translates to an Int but the latter? Since it should be a pointer, I guess it shall be Pointer.SIZE?

However this is my implementation, where VROverlayIntersectionMaskPrimitive_Data_t is an abstract class:

abstract class VROverlayIntersectionMaskPrimitive_Data_t : Structure {

    constructor() : super()
    constructor(peer: Pointer) : super(peer)
}

Implemented in turn by the two other classes.

My first guess is that sizeof(VROverlayIntersectionMaskPrimitive_Data_t) translates to Int + Pointer.SIZE

@JvmOverloads fun setOverlayIntersectionMask(
                ulOverlayHandle: VROverlayHandle_t,
                pMaskPrimitives: VROverlayIntersectionMaskPrimitive_t.ByReference, 
                unNumMaskPrimitives: Int, 
                unPrimitiveSize: Int = Int.BYTES + Pointer.SIZE)

Does my reasoning appear correct?

Answer 1

You obtain the size of a Structure (including Union) with the size() method. In the case of unions, you'll get the size of the largest member.

You set the desired type of the union with Union.setType().