Subtree
Decodes 3D Tiles 1.1 .subtree binary files into Subtree availability tables. Consumed by the implicit-tiling expansion pass when it encounters a tile whose subtree URI template has resolved to a fetched payload.
Spec: https://github.com/CesiumGS/3d-tiles/tree/main/specification/ImplicitTiling#subtrees.
Wire format (header is 24 bytes, little-endian):
bytes 0..3: magic
"subt"(0x73 0x75 0x62 0x74)bytes 4..7: version (uint32, 1)
bytes 8..15: JSON byte length (uint64)
bytes 16..23: binary byte length (uint64)
JSON chunk: describes which bytes of the binary chunk hold which bitstream + any inline constants (all-available shorthand)
binary chunk: packed availability bits, little-endian within bytes
Functions
Parse one .subtree payload. Throws IllegalArgumentException when the header magic / version don't match the spec — easier to surface that early than to silently produce empty bitstreams the traversal code can't distinguish from "everything absent".