remove perf roadmap
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Hakan Seven
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ROADMAP.md
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ROADMAP.md
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# Open CAD Studio — File Open & Render Speed Roadmap
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This document lists the planned improvements for cutting **file open time**
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and **on-screen draw (render) time**. It builds on the already-landed
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**Rendering Optimization** work (Phase 1-4); what is left now sits on the
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open-time, allocation, and draw-call sides.
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Source-scan summary (references):
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- File open flow: [`src/io/mod.rs`](src/io/mod.rs)
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(`open_path_with_phase`, `load_file`, `purge_corrupt_entities`).
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- Post-open UI work: [`src/app/update.rs:90-192`](src/app/update.rs#L90-L192)
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(`FileOpened` handler — xref resolve, second purge, linetype populate, etc.).
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- Derived-cache build: [`src/scene/mod.rs:90-212`](src/scene/mod.rs#L90-L212)
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(`build_derived_caches` — rayon-parallel for hatch / image / mesh).
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- Wire tessellation: [`src/scene/mod.rs:1328-1402`](src/scene/mod.rs#L1328-L1402)
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(rayon, zoom-adaptive curve tol).
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- Block defn cache: [`src/scene/block_cache.rs:238`](src/scene/block_cache.rs#L238)
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(`build_defn` — single-threaded today; nested expansion is topological).
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- Pipeline: [`src/scene/pipeline/mod.rs`](src/scene/pipeline/mod.rs)
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(batched hatch, frustum cull, LOD — Phase 1-4 done).
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---
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## Phase 1 — File Open Time
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**Goal:** measurably halve the wall time between "Open" click and "first
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frame" for a 50 MB DWG.
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### 1.1 Drop the second `purge_corrupt_entities` ✅ DONE
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### 1.3 Single-pass entity walk (parse + purge + cache planning)
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`load_file` → `purge` → `build_derived_caches` does three separate
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`entities()` walks. A single pass can produce:
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- corrupt-entity detection,
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- hatch / image / mesh handle lists,
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- AABB accumulation for `world_offset` (the world_offset AABB scan is now
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folded into the cache-handle walk — see 2.4; corrupt-detect + hatch/image/
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mesh planning remain a follow-up).
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Target: three `O(N)` passes → one.
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### 1.4 Memory-mapped file reads (DWG / DXF)
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`DwgReader::from_file` / `DxfReader::from_file` likely load the whole file
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into RAM with `std::fs::read`. Switching to `memmap2`:
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- eliminates the cold-cache read syscall on large files,
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- lets the DWG section index be walked on disk (if the acadrust API
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supports it).
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**Dependency:** acadrust upstream may need a `from_reader` / `from_slice`
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API; add it in our patched fork (`hakanaktt/acadrust`).
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### 1.5 Parallelize the acadrust parser (long-term)
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acadrust's DWG parser is single-threaded. Section-based parallelism
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(header / classes / objects / blocks / entities — independent offsets) is
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the biggest unrealized win. Lives in the upstream fork.
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**Order:** profile first — is this really the largest slice? Measure with
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`puffin`.
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### 1.6 Defer raster image decode
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[`build_derived_caches`](src/scene/mod.rs#L177-L186) calls
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`ImageModel::from_raster_image` for every `RasterImage` entity — pixel
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decode happens up front. Wasted if the entity is off-screen. Defer the
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decode until **first render** (per-handle lazy `OnceCell`).
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### 1.7 File-hash cache (warm re-open)
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When re-opening the same file (`(path, mtime, size)` key) keep a disk
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snapshot of `CadDocument` + `DerivedCaches` (e.g. `~/.cache/OpenCADStudio/`). Skip
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DWG parse entirely. **Win:** most-recently-opened file goes from 1-2 s to
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sub-100 ms.
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**Risk:** cache invalidation. Stay conservative — load only on exact
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`mtime + size` match, otherwise normal parse.
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---
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## Phase 2 — First-Frame Wire Tessellation
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After `FileOpened`, `bump_geometry()` fires; the first frame tessellates
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**every** model-space wire. Measurable hitch at ~100 k entities.
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### 2.1 Parallelize block-definition build ✅ DONE
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### 2.2 Incremental wire cache (delta tessellation) ✅ DONE (render path)
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### 2.3 Progressive first render
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On the first frame emit a **coarse**-tol wire pass (e.g. 4× the normal
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tol); refine to full tol on the second frame. The user sees *something*
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within 16 ms; detail snaps in smoothly afterwards.
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### 2.4 Merge the world-offset scan into the single-pass walk ✅ DONE
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---
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## Phase 3 — Per-Frame Render Cost
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After Phase 1-4 culling/LOD, what's left is **upload bytes** and **draw
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call count**.
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### 3.1 Camera-only invalidation: don't re-tessellate
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The wire cache key today is `(geometry_epoch, camera_generation)`
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([`scene/mod.rs:414`](src/scene/mod.rs#L414)). A camera change should not
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force re-tessellation — only zoom-adaptive curve-tol changes need
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resampling, and only for curve entities (Arc / Spline / Ellipse). Straight
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geometry is camera-invariant.
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**Practical:** split the wire cache in two:
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- `tess_cache[handle] → WireModel` (rebuild only if tol-invariant content
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changed),
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- `frame_visible[handle] → bool` (recomputed per `camera_generation`).
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Partials already landed: pan reuse, selection/hover decoupled from
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tessellation, per-frame `split_face3d_wires` memoized. **Still open:** the
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full camera/selection-from-tessellation split — highlight colour is still
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baked into `WireModel.color` across several tessellation sites, so finishing
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this needs running-app verification.
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### 3.2 Persistent GPU buffer pool — diff upload ✅ DONE (wire pan path)
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### 3.3 Single-draw batched wire pipeline (Phase 4-B-style) ✅ DONE
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### 3.4 Hardware instancing for repeated block inserts
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When the same block defn is `INSERT`-ed N times (every door / window in
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an architectural drawing) each instance currently renders as its own wire
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set. Hardware instancing:
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- upload the block defn vertex buffer once,
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- one 4×4 transform row per Insert in an instance buffer,
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- `pass.draw_indexed(0..V, 0..N_instances)`.
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Typical architectural DWGs: 10-100× faster.
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### 3.5 Glyph-stroke batching ✅ DONE
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---
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## Phase 4 — Allocation & Memory
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### 4.1 Swap `HashMap` for `rustc-hash::FxHashMap` ✅ DONE
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### 4.2 Arena (`bumpalo`) for transient wire vertices
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Tessellation allocates millions of small `Vec<Vec3>`s. A bump arena —
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single allocation, frame-end reset — kills the per-vertex malloc cost.
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`bumpalo` plays well with rayon (per-thread arenas).
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### 4.3 `SmallVec` for small collections
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`Polyline.vertices`, `Hatch.boundary_paths`, glyph-stroke lists are
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typically < 8-16 entries. `SmallVec<[T; 8]>` skips the heap on the common
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case.
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### 4.4 Compact entity-ID representation
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`Handle` is 8 bytes. 100 k entities → 800 KB just in keys. Hot handle
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HashSet / HashMap usage can be flattened to `Vec<u32>` indices plus a
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single `FxHashMap<Handle, u32>` translation table — cache-friendlier.
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---
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## Phase 5 — Profiling Infrastructure (prerequisite)
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Don't start any of the above **without measuring first**.
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### 5.1 Add `puffin` or `tracy` spans
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- `io::open_path_with_phase` → `parse`, `purge`, `caches` spans.
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- `Scene::wires_for_block` → `block_cache`, `tess`, `sort` spans.
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- `Pipeline::prepare` → `upload`, `cull`, `draw` spans.
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Gate behind `debug_assertions` or a `--features profile` flag.
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### 5.2 Open-time breakdown log ✅ DONE
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### 5.3 Frame-budget HUD ✅ DONE (CPU tess slice)
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---
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## Priority Order
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**Phase 5.1 first** (the remaining profiling span work) — avoids speculation.
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Then, measurement-guided, the remaining items:
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1. **Phase 1.3 + 1.6** (single-pass walk + lazy image decode).
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2. **Phase 3.1** (camera-only invalidation — users pan/zoom constantly; the
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hard part of the tess/selection split is what's left).
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3. **Phase 3.4** (block instancing) — biggest render win, highest complexity.
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4. **Phase 1.7** (warm cache) — dramatic UX, but invalidation must be
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correct or it creates nasty bugs.
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5. **Phase 1.5** (acadrust parallel parse) — hardest, longest-term; only
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worth it if profiling confirms it is the dominant slice.
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## Deliberate non-goals (for now)
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- **GPU compute culling:** for orthographic 2D CAD the CPU quadtree is
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enough. Already covered by Phase 1-4.
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- **Out-of-core entity streaming:** meaningful for 100 MB+ single files;
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typical Open CAD Studio files are not there yet.
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- **Multi-frame async tessellation pipeline:** if 2.3 progressive render
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works cleanly, this isn't needed.
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