The same tree with indexed triangles: each record's original index names
the geometry's triangle, whose vertex indices are written in corner order
(the records' corners are that triangle's, in that order), and flags bits
0-1 move to bits 28-29. A merged record's material and source instance are
not carried (the scene's side table holds them): convert fresh trees.
An indexed layout comes back as it is.
The same tree with indexed triangles: each record's original index names the geometry's triangle, whose vertex indices are written in corner order (the records' corners are that triangle's, in that order), and flags bits 0-1 move to bits 28-29. A merged record's material and source instance are not carried (the scene's side table holds them): convert fresh trees. An indexed layout comes back as it is.