cad-editor/docs/native-vs-web.md

Native vs. Web (WebAssembly)

Open CAD Studio ships as a native desktop app and as a WebAssembly build that runs in the browser (https://hakanseven12.github.io/OpenCADStudio/). Both are built from the same source; the web target drops or shims the pieces that a browser can't provide. This page lists the differences.

At a glance

Area	Native (desktop)	Web (wasm)
Windowing	Multi-window (iced::daemon)	Single window (iced::application); dialogs are in-canvas modals
3D solid modeling	Yes	No — solid3d feature off
Hatch rendering	Yes	No — WebGL2 has no vertex-stage storage
Fonts	Embedded stroke fonts + system TrueType + shaping + fallback	Embedded stroke fonts only
File open	Native file dialog → path	Browser picker → bytes
File save	Path / Save dialog → write to disk	Save dialog → direct browser download
Parallelism	Multi-threaded (rayon)	Single-threaded
GPU backend	Vulkan / DX12 / Metal (wgpu)	WebGL2 (WebGPU where available)
Update check / external links	ureq, open	skipped / window.open

Details

3D solid modeling — web: disabled

The solid3d Cargo feature (default on) gates truck-meshalgo and truck-shapeops, which pull vtkio → xz2 → lzma-sys, a C library that can't cross-compile to wasm32. The web build compiles with --no-default-features, so on the web:

• The Model tab's solid primitives and boolean operations are no-ops.
• Solid tessellation and ACIS (SAT) import produce no geometry.

2-D CAD is unaffected.

Hatch rendering — web: not drawn

The batched hatch pipeline binds a read-only storage buffer in the vertex stage. WebGL2 lacks VERTEX_STORAGE, so that pipeline is skipped on wasm and hatches simply don't render. Everything else (lines, arcs, polylines, text, images) draws normally.

Fonts — web: bundled stroke fonts only

• Native discovers installed system fonts (fontdb), extracts TrueType outlines (ttf-parser), shapes runs with cosmic-text (ligatures, Arabic joining, kerning, bidi), and falls back to a system font for glyphs a stroke font lacks.
• Web has no system fonts, and cosmic-text panics with "no default font found" on an empty font set, so shaping and fallback are disabled. Only the embedded LFF stroke fonts render; a glyph missing from them is skipped. (A future option is to fetch a font file from the server at startup.)

File I/O — web: bytes and downloads

• Open: the desktop returns a filesystem path and reads it (streaming). The web reads the picked file's bytes via the browser and parses them in memory (io::load_bytes).
• Save: both show the in-app Save dialog (filename + format). The desktop writes to the chosen path; the web serializes to bytes and triggers a direct browser download (a Blob + a programmatic <a download> click — no intermediate "click to download" link). The unsaved-changes prompt's Save routes through the same dialog on the web.
• There is no persistent filesystem path on the web, so a name-only path stands in for document tracking.

Windowing — web: single window, in-canvas modals

The desktop uses iced::daemon and opens secondary OS windows for every manager and style dialog. The browser has only the canvas, so the web uses iced::application and renders all dialogs (layer/layout/plot managers, the style editors, the colour picker, Save / unsaved prompts, About, shortcuts, plugins, …) as in-canvas modal overlays. As of the Plan-B work this path is shared: native renders the same modals too, so the desktop is effectively single-window now. A modal's backdrop dims and blocks clicks but does not dismiss; the ✕ button closes it.

Parallelism — web: single-threaded

wasm32 has no threads without SharedArrayBuffer (which needs COOP/COEP headers GitHub Pages can't set). crate::par::prelude re-exports rayon on native and sequential std iterators on wasm, so the same call sites run in parallel on the desktop and serially in the browser. Large drawings are slower on the web.

Platform shims (src/sys.rs)

• open_url: open::that on native, window.open(_blank) on web.
• download_bytes: web only (Blob + anchor download).
• handle_path: real path on native, a name-only PathBuf on web.
• platform_info: OS + arch on native, the browser user-agent on web (used to pre-fill the Send Feedback issue).
• The self-update check (ureq) is a no-op on the web.

Build & deploy

• Native: cargo build --release --bin OpenCADStudio.
• Web: trunk build --release --public-url /OpenCADStudio/ (the rust <link> in index.html sets data-cargo-no-default-features, dropping solid3d). .github/workflows/pages.yml builds and deploys to GitHub Pages on every release. No COOP/COEP headers are needed because the web build is single-threaded.