BREP_render — the wgpu render/pick engine

The windowing-agnostic rendering, picking, and viewer-state engine for the BREP kernel (publishes on crates.io as BREP_render, lib brep_render). It runs a kernel feature history in-process, populates a renderer-agnostic scene store from the resident solids, and draws it with a wgpu 29 core — the same code backing a headless artifact binary, a native winit window, and a browser canvas.

Layering

From src/lib.rs, bottom up:

• scene — the renderer-agnostic scene store (RenderScene): display objects keyed by the same kernel names the feature pipeline mints (per-face triangle ranges + names, edge polylines + names, vertices) with typed metadata. No GPU, no window.
• pipeline — history-request JSON → the kernel's native execute_history (same process, same thread) → scene population from the resident solid handles via the kernel's display accessors. No serialization boundary between kernel and renderer. A failed feature still displays what the history did build, with diagnostics.
• engine_state — [EngineState], the viewer brain every shell wraps: scene + camera + arcball controls + render settings, selection and hover emphasis with a selection filter, picking, the editable feature history (rollback, undo/redo — the single source of truth; UIs keep no copy), sketch mode (in-viewer 2D sketch editing: input, solving, dimensions, inference), widget overlays (transform gizmo, ViewCube, datums, feature dimensions via BREP_gizmos), expressions, and model I/O. No GPU, no canvas — it is fully unit-testable on native, and everything crosses its boundary as plain JSON and scalars.
• render — the wgpu core. RenderCore::render_to_view draws a scene into any wgpu::TextureView (4x MSAA): shaded faces with per-face selection/hover emphasis, screen-constant-width edges with occluded portions dimmed rather than dropped, selected-face boundary outlines, vertex point sprites, overlays. render_to_png adds render-to-texture → readback for headless use. Per-solid GPU buffers are retained while a solid's scene revision is unchanged, so history reruns don't re-upload unchanged solids; the same scene + camera + size + styles produce identical PNG bytes on the same device. The WGSL lives in src/shaders.wgsl (shipped in the package).
• pick — CPU ray/screen-space picking over the scene's display buffers, returning kernel names with VERTEX > EDGE > FACE priority, CSS-pixel thresholds, and a ranked candidate list. Exact, deterministic, and identical on native and wasm.
• camera / controls / view — pure-math cameras (artifact framing, orbit/arcball, ortho/perspective).

The crate re-exports its kernel dependency as brep_render::brep_kernel, so downstream shells can name the run-boundary types (HistoryRequest, …) without taking their own kernel dependency and re-mirroring this crate's kernel feature split.

Presentation shells

The render core never owns a window or canvas; the shells are thin:

• Headless: brep-render-artifact (always built) — brep-render-artifact <history-request.json> <out.png> [width height] runs the whole history natively and writes one framed PNG. History errors are reported on stderr but still produce a frame.
• Desktop (feature desktop): brep-render-desktop <history-request.json> wraps a winit window + wgpu surface around the same EngineState + RenderCore — orbit/pan/zoom, standard views, the ViewCube, and picking all flow through the shared state. Frames are drawn on demand (only when the state is dirty). Off by default so the headless binary builds without windowing dependencies.
• Web (wasm32 only): the engine module is the wasm-bindgen canvas shell — attach/resize/event/camera/pick/scene-feed/settings API over a WebGPU or WebGL2 device (wgpu's webgl feature is enabled). Every dependency on the shared path is wasm32-clean.

The interactive application host is the BREP_app crate, which embeds this engine in an egui frame; dependency chain: BREP_app → BREP_render → { BREP (kernel), BREP_gizmos }.

Build and test

cargo build                                # engine + headless artifact binary
cargo run --bin brep-render-artifact -- history.json out.png
cargo build --features desktop             # + the winit desktop shell
cargo test                                 # native unit tests (EngineState, pick, sketch, …)

The crate is standalone (not a workspace member) on purpose: the kernel's own Cargo.toml carries wasm-specific profile settings that a workspace root would override. Native builds link the kernel with its parallel tessellation feature; the wasm build deliberately does not.

License and links

• License: the repository's Autodrop3d LICENSE.md (license-file in the manifest).
• Repository: https://github.com/mmiscool/NURBS_BREP_kernel (this crate lives in BREP_render/).
• The crate family is ready to publish but deliberately unpublished — see /PUBLISHING.md at the repository root for the order and validation.