This is an equivalent of the point cloud index class, with some
notable differences:
- The class is designed to be thread safe. There's a shallow copy
QgsTiledMeshIndex class, which contains an implicitly shared
QgsAbstractTiledMeshIndex object. Tiled mesh data providers will
be accompanied by a concrete class of QgsAbstractTiledMeshIndex.
- The QgsTiledMeshIndex class takes care of thread safety by
protecting the underlying QgsAbstractTiledMeshIndex via a read/write
lock
- Callers can request tiled mesh tiles from the index by calling
QgsTiledMeshIndex::getTiles along with a QgsTiledMeshRequest object.
This will return the unique IDs of tiles matching the request.
Currently only geometric error based filtering is supported
by QgsTiledMeshRequest, but bounding box based filtering will
also be introduced.
- Individual tile details are retrieved by calling
QgsTiledMeshIndex::getTile along with the tile's unique ID.
- A caller can determine whether a specific tile can be further
refined by checking QgsTiledMeshIndex::tileCanRefine. This allows
the caller to check whether more children are available for a
tile, but which haven't yet been fetched (eg due to a sub dataset
tileset which hasn't yet been retrieved)
- A tile can be refined by calling QgsTiledMeshIndex::refineAsync.
(Non async refinement will be introduced later)
- Clients can request tile content by calling
QgsTiledMeshIndex::retrieveContent. This will either return
a cached version of the content (if available), or retrieve and cache
the content for future retrieval. Currently this uses a custom caching
mechanism, but this will be replaced in future with
QgsTileDownloadManager. (Currently QgsTileDownloadManager lacks support
for blocking gets which is required by the index to avoid use
of local event loops)
The api is implemented by the cesium tiles data provider, which
builds the index upfront from the cesium tiles tileset.json definitions.
Avoids an upfront cost of handling map theme overrides when loading
legend items in layouts, where the legend is linked to a map
with a map theme set.
This cost will still be incurred later, when the layout is opened.
(The actual root cause of this issue is the EXTREME cost of applying
layer presets in order to retrieve the definition of map themes, but
that's far from trivial to fix)
