Eliminate intermediate heap vector allocations during wire classification
and analytical instance extraction for circle and ellipse GPU pipelines.
1. Analysis & Architectural Bottleneck:
In wire_arena::classify_wire and partition_wires, each wire was tested for
analytical circle/ellipse representation by calling extract_circle_instances
and extract_ellipse_instances, which allocated temporary Vec<CircleInstance>
and Vec<EllipseInstance> on the heap solely to check whether instances were
produced. Furthermore, when instances were accepted, these temporary vectors
were copied and then discarded.
2. Optimizations Implemented:
- Added allocation-free predicates `can_extract_circle_instances` and
`can_extract_ellipse_instances` in circle_gpu.rs and ellipse_gpu.rs.
- Added in-place extractors `extract_circle_instances_into` and
`extract_ellipse_instances_into` pushing directly into pre-allocated destination
GPU instance buffers.
- In wire_arena.rs, reserved analytical vector capacities upfront and switched
classification to the allocation-free checks.
- In pipeline/mod.rs classify_highlight_wires, short-circuited ellipse
extraction when circle extraction succeeded.
3. Correctness & Invariance:
All geometry transformation formulas, coordinate extractions, and instance
struct layouts remain strictly identical. Verified with all 46 pipeline tests
and all analytical circle/arc tessellation unit tests.
4. Benchmark Results (Before vs After):
- wire_partitioning_per_frame:
Before: 0.18 ms (mean 0.19 ms, p95 0.38 ms)
After: 0.06 ms (mean 0.07 ms, p95 0.28 ms)
Improvement: -63.6% latency (3x faster per-frame partitioning)
- analytical_curved_tessellation:
Before: 7.79 ms (359.5k entities/s)
After: 6.87 ms (407.7k entities/s)
Improvement: -11.8% latency (+13.4% throughput)
- wide_and_tapered_arc_tessellation:
Before: 6.36 ms (235.8k entities/s)
After: 5.48 ms (273.8k entities/s)
Improvement: -13.8% latency (+16.1% throughput)
- analytical_curved_zoom_100x:
Before: 12.75M FPS (0.01 ms)
After: 13.97M FPS (0.01 ms)
Improvement: +9.6% FPS
- Repurpose CircleInstance center_high.w and params.w for start_width and end_width (preserving exact 128-byte stride)
- Route wide polylines, tapered polylines with bulges, and donuts through split_mixed_polyline into GPU analytical arc instances
- Compute physical annular bands, width tapers, and round end caps in circle.wgsl using world-space distances to prevent 3D perspective foreshortening distortion
- Expand bounding quad margins dynamically with grazing-angle compensation to eliminate clipping
- Relax pick_tris check in wire classification and partition routines so wide entities retain CPU picking while drawing analytically
- Add unit and hardware GPU integration tests, including tilted 3D perspective rendering verification
- Emit transformed analytical curves (circles, arcs, ellipses) in block
expansion as standalone wires rather than merging them into batched line
strips.
- Keep render_instance unset on analytical curves in block prototypes so
they route directly to CircleGpu / EllipseGpu instead of BlockWireGpu.
- Support TangentGeom::Circle in extract_circle_instance and wire partitioning.
- Drop analytical tangents on wires clipped by xclip so clipped geometry
falls back correctly to line segments.
- Add unit test verifying block circles and arcs extract as analytical GPU
instances.
Karim Jerbi