Two ways to get item's inverted world transform matrix.

wxfrmInvert.cpp

/*
 * This snippet demonstrates two of the ways to obtain item's inverted world transform matrix.
 */

// --- METHOD 1 
CLxUser_Scene scene;
item.Context (scene);

CLxUser_ChannelRead chanRead;
CLxUser_SelectionService selSvc;
scene.Channels (NULL, selSvc.GetTime(), chanRead);

// Get world transform matrix via channel read. This matrix is not mutable.
CLxUserMatrix mtx;
chanRead.Object (item, "worldMatrix", mtx);

// Pull matrix array from the matrix object.
LXtMatrix4 xfrm;
mtx.Get4 (xfrm);

// Create new value of type matrix. We will copy the matrix array into it.
CLxUser_ValueService valSvc;
CLxUser_Value invMtxVal;
valSvc.NewValue (invMtxVal, LXsTYPE_MATRIX4);

// Create new matrix interface and set it to our mutable matrix value.
// Finally set the matrix array from the one copied from original matrix
// and call invert method.
CLxUser_Matrix invMtx;
invMtx.set (invMtxVal);
invMtx.Set4 (xfrm);
invMtx.Invert ();

// --- METHOD 2
// This is similar to the above but we read value object from channel read
// directly, then create new user value and copy world transform value into it.
// Then, just like above, we create new matrix interface, cast it to the newly
// created value and use invert method.
CLxUser_Scene scene;
item.Context (scene);

CLxUser_ChannelRead chanRead;
CLxUser_SelectionService selSvc;
scene.Channels (NULL, selSvc.GetTime(), chanRead);

unsigned int wmtxChanIdx;
item.ChannelLookup ("worldMatrix", &wmtxChanIdx);
CLxUser_Value mtxVal;
chanRead.ValueObj (item, wmtxChanIdx, mtxVal);

CLxUser_ValueService valSvc;
CLxUser_Value invMtxVal;
valSvc.NewValue (invMtxVal, LXsTYPE_MATRIX4);

invMtxVal.Copy(mtxVal); // Copy FROM

CLxUser_Matrix invMtx;
invMtx.set (invMtxVal);
invMtx.Invert ();