akgl_Partitioner is a record of function pointers and an initializer, the same
shape as the render and physics backends. `move` is its own slot rather than
remove-then-insert, and that is the whole design: a uniform grid's move is a
comparison and a return when the proxy has not left the cells it was in, which
is the steady state for a walking actor and the permanent state for a static
one. Spelling it as remove-and-insert would turn the incremental grid into the
rebuild-every-frame tree that PERFORMANCE.md already measured and rejected.
The grid is a dense 128x128 array of cell heads over the world, cells keyed on
tile size, with two intrusive chains per entry -- one through the cell so a query
can walk it, one through the proxy so removal unlinks a whole span without
searching. Everything is an int16_t index rather than a pointer, so the
structure is relocatable and clearing it is a memset. A proxy covering more
cells than AKGL_COLLISION_GRID_MAX_SPAN spills onto one chain every query walks,
which is what makes the cell pool's ceiling provable rather than hopeful.
tests/partition.c compares every query against a linear scan over the same
proxies and asserts containment in one direction, not equality. That asymmetry
is the contract: over-reporting costs a narrowphase call, under-reporting is a
wall an actor walks through. The suite is a table over partitioners so the same
assertions run against every implementation, which is what the second one
landing later will be held to.
Three deliberate breaks, and two of them were not caught the first time:
- Removing the min-cell rule so a shared-cell pair reports repeatedly: caught.
- Dropping the unlink in `move`: **not caught**, initially. Stale entries do not
produce wrong query answers, because the bounds re-check filters them out --
they leak the cell pool until the grid stops working, on a timescale no unit
test reaches by accident. Counting live pool entries across 200 moves is the
only thing that sees it, and now does: 505 entries against an expected 5.
- Swapping floorf for a truncating cast: **not caught, and correctly so.**
Everything below zero is clamped to cell 0 either way, so today the two are
indistinguishable. The comment claiming truncation is a defect was overstating
it and now says what is actually true: the clamp is the only thing hiding it,
and a negative world origin or a relaxed clamp would make it real with no test
standing in front of it.
Co-Authored-By: Claude Code <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Andrew Kesterson
68e042bd47
