The texcoords are 12-bit fixed on 82.5% of vertices, not 100%, and the residual
had no explanation. Grouped by the vertex's i16[3] slot across 95,612 vertices on
levels 0-2, the buckets separate completely:
i16[3] n % / 4096 % / 256
negative 333 1.2% 1.2%
== 0 5,851 29.2% 60.7%
1..63 28,884 92.7% 94.3%
64..255 54,606 92.3% 93.8%
256..511 8 0.0% 0.0%
512..1023 5,391 0.0% 0.0%
>= 1024 539 0.2% 0.2%
The residual is fully accounted for. 87.3% of vertices sit in 1..255 at about 92.5%
fixedness, contributing 0.873 * 0.925 = 80.8 points; the 5,851 at i16[3] == 0
contribute 1.8 more. That is the 82.5% measured, to the point.
The remaining ~6% are not 12-bit fixed at all. i16[3] >= 256, and negatives, score
0% at BOTH 4096 and 256 -- 6,271 vertices in an encoding this reading does not
see. And i16[3] == 0 scores 29.2% at 4096 but 60.7% at 256, which is a third
distribution rather than a weaker version of the same one.
What this establishes: i16[3] is a per-vertex packed attribute whose value SELECTS
HOW the texcoord pair is stored, rather than an independent field sitting beside
the texcoords. 1-255 is the ordinary case, 0 is special, 256-and-up and negatives
are a different encoding. What those three cases MEAN is still open -- texture
index, normal index, flag or a combination -- but it is now a field whose role is
known, which is more than "packed word".
Worth noting the shape of the claim this replaces: "the texcoords are 12-bit fixed
at i16[4]/i16[5], 73.6% of the time, unexplained". The field position was right;
the 73.6% was a population average over three encodings. Partitioning by the one
variable that separates them turns a mystery into a lookup -- rule 3a again, and the
third time this session that partitioning a mystery produced the answer rather than
merely bounding it.
ReaperOfVeriod
e27c40e738