Printing the region table next to the header fields makes the gap visible
without having to remember to consult core_layout, and it paid for itself
immediately.
On level 0 the collision region comes out 6216960 bytes, from 2615232 to
the first moby class at 8832192. Collision's own header declares a payload
of 903,248. So roughly 6.2 MB sits between the collision header and the
first moby class, and almost none of it is collision.
The successor rule is correct -- a region does end where the next one
begins -- but "the next" is not yet known there. collision..moby is
really collision + <something unnamed> .. moby. The name is wrong, not
the bound.
Candidates for the space, rough order of likelihood: moby and tie model
animation data, which is what moby_anim would need, then volumes, then
per-class runtime structures. Tfrag texture texels are already placed and
sit earlier in the lump.
Worth resolving before starting moby_anim, since that format is the most
likely tenant. Until then, any probe reading between the collision header
and the first moby class is reading something the region table does not
describe.
Region spans were being re-derived per format while probing, usually
running from one known offset to the next with the last span running to
core_data.len(). On level 0 that gave the final shrub class a 925,008-byte
span absorbing most of the lump's tail, and every aggregate computed over
it -- record counts, value distributions, "this looks random" -- was
silently wrong. Nothing errored, which is what made it survive two
commits and a correction.
core_layout computes the layout once: each region ends where the next one
begins, class regions start at the lowest non-zero geometry offset in their
table, and a region whose successor is unknown gets end: None rather than a
clamped guess. Zero class entries mean absent, not position zero -- the
same trap occlusion and collision each fell into separately.
The disc test asserts what the module is actually for: that the unknown is
visible. Shrub's end is unresolved on the 24 levels that have a shrub
region, and that is asserted rather than hidden.
It also found that not every level has every region -- level 10 has neither
occlusion nor shrub -- so the test checks ordering against the canonical
sequence instead of demanding an identical set.
Still open: where the shrub region ends. Texture texels cannot bound it;
they sit before moby, not after shrub. See docs/formats/core-data-regions.md.
ReaperOfVeriod