jpx_source::access_composition

Use this function to gain access to the jpx_composition object, to learn the contents of any composition box, describing complex multi-layer compositions and/or animation.

An empty interface (one whose jpx_composition::exists member returns false) if the composition box cannot yet be fully parsed. This can happen only if the ultimate source of data is a dynamic cache which does not yet have sufficient data. In many cases, the composition box may become available before the composition layers to which it refers can be opened, but the opposite may also be the case.