BuildTLAS
- A rebuild for a new instance count or build preference used to create a
new acceleration structure and destroy the old one at once, though the
command buffer being recorded could still use it (a scene and then a
model built in one setup). The acceleration structure now spans its whole
storage buffer, and a rebuild that fits builds into it again, so the
handle and tlases[i].address stay the same and nothing is destroyed. A
TLAS that outgrows its storage gets new storage and a new handle; the old
handle goes to the deletion queue ahead of the storage it lives in. It is
queued after the scratch is resized, and its address goes with it, so a
Resize or create that throws leaves no address of a queued acceleration
structure behind.
- The barrier before the build also orders earlier traces and compute ray
queries of the TLAS, which a refit or a rebuild in place would otherwise
overwrite while they read it (BuildTlasWriteBarrier). Its source access
mask holds no read bit: one does nothing, but makes synchronization
validation 1.4.363 report the second of two builds in one command buffer
as a write-after-write hazard.
- TlasReadBarrier is now TlasBarrier, shared by both barriers.
- Documented: call BuildTLAS once every earlier submission that used
tlases[index] has completed, and when the address stays the same.
TlasWithBuffer
- Moves hand the acceleration structure over, and destroying or assigning
over one queues it ahead of its storage. The implicit members dropped the
handle over freed storage, or left two owners and a moved-from TLAS that
refit through buffers it no longer had.
Tests
- TLASLifetime: destroying, moving, move-assigning and resetting a
TlasWithBuffer.
- TLASHighWaterMark skips without ray tracing. It asserts the acceleration
structure is rebuilt in place on a shrink or a growth within capacity,
that the old handle is queued before its storage on a growth past it, and
that builds in one command buffer keep the handle while they fit, queue
it once when one outgrows the storage, and free it only on its retire
frame.
- TLASBuildBarrier checks the barrier before the build too.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Jorijn van der Graaf
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