`PersistentWireArena` keeps one instance buffer for the whole resident
set and patches it in place on an edit. Sizing that against the shared
per-chunk budget caps it at 32 MiB, which is 524 288 `WireInstance`s.
A drawing with more than that fails `WireArena::build`, falls back to the
batched path, and re-uploads everything on every edit. On the 198 k-wire
reproducer -- 821 316 instances -- that shows up as:
wire 200-370ms arena-hybrid
instead of the ~12 ms `arena-patch` the same drawing reached before the
limits moved onto the shared budget.
The 32 MiB cap is right for transient chunks, where many are allocated
per frame and any one of them failing loses the frame. The arena's buffer
is a single long-lived allocation that exists precisely to avoid those
re-uploads, and it can afford more: 821 k instances is 53 MB, ~79 MB with
the arena's headroom. 128 MiB leaves it four times smaller than the
505 MiB allocation that crashed a 2 GB card, and it is allocated through
`gpu_upload`, so exhausting VRAM still degrades the frame rather than
aborting.
`OCS_GPU_CHUNK_MIB` overrides both caps, so a test can still force small
buffers everywhere.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
max_buffer_size is an API validation limit, not physical VRAM. NVIDIA
reports several GB of it on a 2 GB card, so sizing a chunk from it
produces buffers larger than the whole device. That is the same bug as
#203 (mesh_gpu), #358 (face3d_gpu) and the block-wire vertex buffer:
rediscovered three times because each upload path spelled the budget out
for itself.
mesh_gpu.rs was the only site that clamped the result. Move that clamp
into src/scene/pipeline/gpu_budget.rs and route every allocating path
through it, so a new upload path cannot reintroduce the mistake by
copying one of the unclamped expressions.
Five sites had no clamp at all: text_gpu (block-text instances),
wire_gpu (block-wire instances), and face3d_gpu (vertices, instances,
and upload_chunks).
Three behaviour changes worth noting:
* Silhouette chunks were capped at a private 64 MiB constant and now
use the shared 32 MiB budget.
* The storage-hatch chunk limit was the minimum of two device limits,
both of them validation figures; it is now also capped by the
budget. The `*_fits` predicates next to it are genuine "would wgpu
reject this" checks and are left alone.
* mesh_gpu's instanced path used the unclamped ceiling to decide
whether a mesh fits in a single buffer, which would still admit a
multi-GB allocation. It now uses the clamped budget, so a few more
meshes take the chunked path.
OCS_GPU_CHUNK_MIB overrides the cap. Raising it above the real VRAM is
the cheapest way to force an allocation failure and check that the
renderer degrades instead of aborting.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Hakan Seven