Reject frustum-visible objects whose bounding sphere projects below a
pixel-radius threshold. Applied at both BVH-node level (whole subtrees
pruned) and per-instance level; short-circuits when the camera is
inside the AABB so nothing-you're-standing-next-to is ever lost.
Pick pass passes threshold 0 so sub-pixel objects stay clickable.
Threshold defaults to 2 px (radius), overridable via IFC_MIN_PX env
var. Measured on the 128 M-tri test scene (GTX 1650):
0 px (off): 6.7 fps, 128 M tris
2 px: 20.2 fps, 40 M tris (31%)
4 px: 30.3 fps, 15 M tris (12%)
The metric is sphere-based (cheap: one sqrt per test) rather than
AABB-corner projection; loses a little precision on very elongated
bounds but costs ~5x less per test and the BVH-node pre-cull means
the long-tail-of-small-things case is already handled by subtree
pruning before we touch individual instances.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Earlier probes pointed at per-frame glNamedBufferSubData uploads as the
bottleneck (60 fps when those two calls were commented out). That was a
false reading — zeroing the uploads also emptied the indirect buffer, so
MDI drew nothing. "No upload" and "no draw" were indistinguishable.
Two new diagnostic env vars in render() isolate the real costs:
IFC_SKIP_MDI=1 keep cull + upload + binds, skip only the MDI
draws. Gives 62 fps with everything else running,
confirming the non-draw path fits in ~16 ms.
IFC_MAX_SUBDRAWS=N cap each MDI's drawcount. 67k -> 30k sub-draws
saves 0 ms, confirming sub-draw count itself is
not the bottleneck; the long tail of sub-draws
carries ~no triangles.
On a GTX 1650 with 128 M triangles in view, nvidia-smi sits at 95 %
GPU util and FPS scales with triangle work, not sub-draw count. The
card is simply rasterising at ~850 M tri/s. No CPU-side or upload
trick recovers it.
Revised Phase 3 is therefore shedding triangles, not bytes:
3A screen-space contribution culling (next)
3B LOD
3C HiZ occlusion
3D GPU-side compute culling
README Phase 3 section rewritten around the diagnosis, including the
false lead, so future work doesn't re-tread the upload path. The
aborted staging+resident ring-buffer implementation was reverted (the
uncommitted working tree is gone — pure glNamedBufferSubData retained
for the visible + indirect buffers, which we now know is fine).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
The previous README described a pre-instancing world (32-byte world-
coord vertices with per-vertex object_id, ObjectDrawInfo structs, EBO
reordering after BVH build, and a Phase 3 plan built around moving
draw submission to the GPU). Most of that is either gone or already
solved:
- Vertices are now 28 B local-coord; per-instance transforms live
in an SSBO read through a visible-index SSBO and gl_BaseInstanceARB.
- ObjectDrawInfo is replaced by MeshInfo + InstanceCpu + InstanceGpu.
- No EBO reorder on BVH build — the BVH is over instance AABBs and
the mesh/EBO layout is orthogonal.
- Draw-call submission is already one glMultiDrawElementsIndirect
per model; the old Phase 3 goal is met.
New content worth keeping:
- GPU instancing section documents the mesh/instance/visible/indirect
buffer contract the whole renderer hangs off of.
- Reflection-aware two-pass draw is documented (det<0 placements,
forward/reverse slice split, glFrontFace toggle).
- reorient-shells and backface culling are called out as correctness
+ perf levers with their tradeoffs.
- Phase 3 is rewritten around the actual bottleneck surfaced by
profiling: per-frame glNamedBufferSubData stalls on the visible
and indirect buffers. Includes the diagnostic methodology (empty-
screen jump to 60 fps, window/MSAA invariance, upload-comment-out
experiment) so future-me remembers why this is the next step.
- 3A (persistent mapped ring buffers, near-term) and 3B (GPU-side
compute cull, longer-term) split out with scope estimates.
- Roadmap updated: instancing / MDI / reflections / reorient-shells
/ backface cull all ticked; 3A surfaced as the next open item.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Enables GL_CULL_FACE by default (user-toggleable in Settings) so
closed solids skip shading their back halves. The catch is that
IFC placements can contain reflections (mat4 with det<0 — mirrored
families, symmetric instances). Naively culling would make every
mirrored instance vanish because the rasterizer sees its screen-space
winding as backwards.
Fix: detect reflections at upload time via determinant sign, bucket
visible instances into forward (det>=0) and reverse (det<0) per mesh
during culling, and issue two glMultiDrawElementsIndirect calls per
model with glFrontFace toggled CCW/CW between them. The indirect
buffer is still one buffer — just split into a forward slice followed
by a reverse slice, with m.indirect_forward_count recording the split.
Vertex shader flips the normal when the transform has negative
determinant, keeping lighting correct on mirrored instances. The
fragment shader keeps the gl_FrontFacing fallback as a safety net
when culling is disabled (e.g. for files with open shells).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
IFC files routinely have IfcConnectedFaceSets whose faces point
inconsistently within the same shell — the result under per-vertex
normals is dark inside-out patches, and under GL_CULL_FACE it's
swiss-cheese. reorient-shells fixes the face winding at geometry
generation time, which is the only place it can be fixed correctly;
no shader trick can recover from a mesh whose triangles disagree
among themselves.
Off by default in IfcOpenShell because it adds iterator time, but
we cache the result in the sidecar so it's a one-shot cost per file.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Two bugs conflated as "weird colors":
1. Two-sided lighting. IFC placements often embed reflection
matrices (mirrored families). Transforming a_normal by
mat3(inst.transform) produces a normal pointing the wrong way
on those instances, and max(n·L, 0) then clamps the surface to
pure ambient — reads as dark / washed out. Use gl_FrontFacing
to flip n in the fragment shader so both winding orientations
shade correctly. The proper fix (ship an inverse-transpose
normal matrix or a det-sign bit per instance) is still owed;
that would unlock re-enabling GL_CULL_FACE for a big fragment-
work win on closed solids.
2. Stats label "inst_draws" was counting indirect sub-draws, not
actual GL draw calls — misleading since MDI collapses N sub-
draws into one glMultiDrawElementsIndirect. Split into
gl_draw_calls (real GL calls, = drawn-model count) and
indirect_sub_draws (packed sub-commands). For a BIM model
with 47k unique meshes at full view this now correctly reads
"1 gl_draws (47092 sub)" rather than suggesting 47k driver
dispatches.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Each visible model now issues a single glMultiDrawElementsIndirect
call instead of one glDrawElementsInstancedBaseVertex per mesh. The
CPU BVH cull populates an array of DrawElementsIndirectCommand
records plus the flat visible-instance list, uploads both, and draws
the whole model in one GL call.
Vertex shaders switch from a uniform u_instance_offset to
gl_BaseInstanceARB (ARB_shader_draw_parameters), so per-draw offset
comes from the indirect command's baseInstance field.
Draw-call counts for BIM scenes with hundreds of unique meshes drop
from hundreds-per-frame to one-per-model, cutting driver overhead.
This also sets up the plumbing for the follow-up compute-shader cull
that will populate the indirect buffer entirely on-GPU.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Pre-allocate the instance SSBO on model creation (4 MB, grow-on-demand)
and append each arriving InstanceChunk directly to the GPU-side
InstanceGpu array in uploadInstanceChunk. This makes a model drawable
as soon as its first mesh + first instance chunk land, rather than
waiting for finalizeModel.
The visible-list architecture already decouples SSBO order from the
draw path, so appending in insertion order is correct — no sorting
required. finalizeModel collapses to:
- compute per-mesh instance counts (for stats + sidecar round-trip)
- build the per-model BVH over instance world AABBs
Render / pick loops now gate on ssbo_instance_count > 0 rather than
the finalized flag. Stats include in-progress models in totals
(excluding only hidden).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Re-wires the BVH acceleration structure on top of the new instanced
renderer. Per model, build a BVH over per-instance world AABBs at
finalize (and on sidecar apply). Each frame, traverse the BVH against
the camera frustum to produce a visible-instance index list, bucket by
mesh_id, and upload to a per-model SSBO at binding=1. The main and
pick vertex shaders do a double-indirection
`instances[visible[u_offset + gl_InstanceID]]` so draws only touch
instances that passed the frustum test.
Models with fewer than BVH_MIN_OBJECTS instances skip the BVH build
and fall back to a linear per-instance frustum test.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Commit B of the instancing migration. The sidecar on-disk format is
reintroduced at version 4 with MeshInfo + InstanceCpu sections in place
of v3's flat per-object draw-info array.
After streaming finishes, MainWindow asks the viewport for a post-
finalise snapshot (VBO + EBO are read back from the GPU, meshes and
instances come from the CPU-side arrays) and writes it alongside
PackedElementInfo + the string table. On a subsequent load,
readSidecar rehydrates the whole struct and ViewportWindow::
applyCachedModel uploads VBO/EBO/SSBO in a single step, bypassing the
iterator entirely.
Staleness check is still by source file size.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Commit A of the instancing migration (Phase 3a). The streamer now runs
the iterator with use-world-coords=false and dedupes by the geometry's
representation id, emitting a MeshChunk once per unique geometry and an
InstanceChunk per placement. The viewport keeps geometry in local
coordinates (28 B/vertex, down from 32) and applies the per-instance
transform in the vertex shader via an std430 SSBO indexed by
gl_InstanceID + a per-draw uniform offset. After streaming finishes
finalizeModel() stable-sorts instances by mesh_id, assigns each mesh a
contiguous range, and uploads the SSBO; render then issues one
glDrawElementsInstancedBaseVertex per mesh.
BvhAccel is reshaped to operate on a generic BvhItem (world AABB +
model_id) so it can drive instance-level culling, but the path is not
wired in yet -- every instance is drawn every frame in this commit.
Progressive-during-streaming rendering is likewise disabled: a model
appears when its SSBO is uploaded, not incrementally. Sidecar cache
is stubbed (reads miss, writes are no-ops); the v4 on-disk format with
MeshInfo + InstanceGpu sections lands in Commit B.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
When a BVH leaf passes the frustum test, emit a single glMultiDrawElements
record covering the leaf's entire index range instead of one per object.
Leaves are contiguous in the EBO after reorderEbo, so the range is just
[first_object.index_offset, sum(index_count)]. Cuts draw calls by ~8x
(BVH_MAX_LEAF_SIZE) and shifts the bottleneck from CPU/driver per-draw
overhead toward GPU vertex throughput.
Per-object features (selection highlight, per-vertex color, object_id
picking) are unchanged — they operate on vertex attributes, not draw
state. Future per-object hide/override will use SSBO lookups sampled
by object_id in the fragment shader.
Slight overdraw from skipping per-object frustum tests within a leaf is
negligible given median-split BVH tightness and spare tri throughput.
Also adds visible_objects_ counter so stats still report true object
counts (not leaf counts), plus leaf_draws/model_draws breakdown in the
per-second frame log.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Per-second frame log reports fps/ms, visible/total object & triangle
ratios, VRAM breakdown (VBO+EBO), model count, and pending uploads.
Upload-complete log includes per-model VBO/EBO MB and scene total VRAM.
Streamer runs an instancing analysis keyed on geom.id(): total shapes,
unique representations, dedup ratio, theoretical VBO/EBO/SSBO sizes if
instanced, potential savings, and top-5 most-duplicated representations.
Used to validate whether GPU instancing is worth the architectural
rewrite for a given dataset.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Phase 2 performance: BVH acceleration with median-split build, per-model
trees, and EBO re-sorting for GPU cache coherence. Raw binary .ifcview
sidecar stores full geometry + BVH for instant subsequent loads (skip
tessellation entirely).
Per-model GPU buffers (VAO/VBO/EBO per model) eliminate cross-model buffer
copies on growth. Sidecar reads happen on a background thread. Bulk GPU
uploads are progressive (48 MB/frame chunks) so the viewport stays
interactive while multi-GB models stream in.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Reflect current architecture: per-model streamers, glMultiDrawElements
with frustum culling, 32-byte vertex format with color, multiselect
file picker, settings/stats files.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Introduce ModelHandle and per-model GeometryStreamers so multiple IFC
files can be loaded simultaneously. Object IDs are globally unique
(monotonically increasing across models). File picker is now multiselect.
Each model gets a top-level tree node. Property lookup uses the correct
model's ifcopenshell::file. ViewportWindow supports hide/show/remove
per model via model_id filtering in the frustum cull pass.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Show FPS, frame time, visible/total objects, and visible/total
triangles in the status bar. Toggled via Settings > Show Performance
Stats, persisted in app settings.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Track per-object AABB and index range during upload. Each frame,
extract frustum planes from the view-projection matrix and cull
objects whose AABB is entirely outside any plane. Draw only visible
objects via glMultiDrawElements. Document the three-phase rendering
performance strategy in README.md.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Dion Moult