kdu_compressed_source::set_tileheader_scope

This function should be implemented by sources which support non-sequential code-stream organizations, (i.e., sources which advertise the KDU_SOURCE_CAP_CACHED capability). The principle example which we have in mind is a compressed data cache in an interactive client-server browsing application. Subsequent reads will transfer the contents of the tile header, starting from immediately beyond the first SOT marker segment and continuing up to (but not including) the SOD marker segment.

Cached sources have no tile-parts. They effectively concatenate all tile-parts for the tile and the information from all header marker segments from all tile-parts of the tile. Tile-parts in JPEG2000 are designed to allow such treatment. Cached sources also have no packet sequence. For this reason, the sequence order in COD marker segments and any sequencing schedules advertised by POC marker segments are to be entirely disregarded. Instead, precinct packets are recovered directly from the cache with the aid of the set_precinct_scope function.

If the requested tile header has not yet been loaded into the cache the present function should return false. Many tile headers may well have zero length, meaning that no coding parameters in the main header are overridden by this tile. However, an empty tile header is not the same as an as-yet unknown tile header. The false return value informs the code-stream machinery that it should not yet commit to any particular structure for the tile. It will attempt to reload the tile header each time kdu_codestream::open_tile is called, until the present function returns true.

False if the KDU_SOURCE_CAP_CACHED capability is not supported or if the tile header is not yet available in the cache.

tnum [int]

num_tiles [int]