viewer

Imported from joescohen/sysml-bridge (tools/viewer/AGENTS.md). Install upstream with npx skills add joescohen/sysml-bridge --skill viewer. Copyright stays with the author.

sysmlv2-gui Development Guide

Project Overview

Lightweight SysML v2 graphical viewer/editor in Rust with egui. Renders the graphical notation prescribed by OMG SysML v2 (formal/25-09-03). Runs as a native desktop app (OpenBSD, Windows) and as a web app (WASM/WebGL) from the same codebase. Coordinates with external tools rather than reimplementing their functionality.

Build & Run

Native

cargo build                # debug build
cargo build --release      # release build
cargo run                  # run debug
cargo clippy               # lint
cargo test                 # run tests

Web (WASM)

rustup target add wasm32-unknown-unknown   # one-time setup
cargo install trunk                        # one-time setup
trunk serve                                # dev server with hot reload
trunk build --release                      # production build to dist/

Container

docker build -t sysmlv2-gui .
docker run -p 8080:8080 -v /path/to/models:/models sysmlv2-gui

Deployment Targets

This project targets three deployment modes. All share the same Rust rendering code.

Native Desktop (OpenBSD primary, Windows, Linux, macOS)

• eframe with glow backend (OpenGL ES 2.0+ / OpenGL 3.2+)
• Direct filesystem access, CLI validator, file watching
• Primary development and testing platform: OpenBSD

Web Application (WASM/WebGL)

• Same eframe/glow code compiles to WASM; glow maps to WebGL
• Two use cases:
  • Demos on decisym.ai: prospects interact without installing
  • Enterprise/DoD deployment: containerized web service for managed assets that prohibit software installation
• File access and validation via backend API (not local filesystem)

GPU Acceleration (Future)

• Switch from glow to wgpu via Cargo feature flag for GPU-intensive views (large graphs, force-directed layout)
• wgpu targets DX12 (Windows), Vulkan (Linux), WebGPU (browsers)
• OpenBSD stays on glow (no Vulkan)
• Application code does not change; only the eframe backend feature

Architecture

Module Structure

src/
  main.rs          -- entry point, eframe setup (native + web)
  app.rs           -- top-level App implementing eframe::App
  model/           -- SysML v2 model representation
    mod.rs         -- element types, relationships, containment
    parse.rs       -- .sysml file parser (structural, not semantic)
  render/          -- graphical notation rendering
    mod.rs         -- view rendering dispatch
    elements.rs    -- definition/usage rectangles, compartments
    connectors.rs  -- relationship lines, arrowheads, decorations
    ports.rs       -- port symbols on element boundaries
    layout.rs      -- automatic element positioning
    frame.rs       -- diagram frame with view type tab
  panels/          -- UI panels
    browser.rs     -- model element tree (egui_ltreeview)
    canvas.rs      -- diagram canvas (egui Painter)
    properties.rs  -- element property editor
    validation.rs  -- validation output display
    source.rs      -- textual notation viewer
  platform/        -- platform abstraction
    mod.rs         -- trait definitions for file I/O and validation
    native.rs      -- filesystem + CLI validator (cfg not wasm)
    web.rs         -- HTTP API client (cfg wasm)
  validator.rs     -- interface to validate-sysml CLI (native)
  watcher.rs       -- file system watching for live reload (native)

Platform Abstraction

File I/O and validation differ between native and web. Abstract behind traits and use #[cfg(target_arch = "wasm32")] to select the implementation:

pub trait ModelSource {
    fn load(&self, path: &str) -> Result<String>;
    fn watch(&self, path: &str, callback: impl Fn());
}

pub trait Validator {
    fn validate(&self, content: &str) -> Vec<Diagnostic>;
}

• Native (platform/native.rs): reads files from disk, calls validate-sysml as a subprocess, uses notify for file watching.
• Web (platform/web.rs): fetches model text from a backend API, posts content for server-side validation, no file watching (uses polling or WebSocket for updates).

Key Design Rules

1. Definitions get sharp corners, usages get rounded corners. This is the fundamental visual rule of SysML v2. Never mix them up.

2. The model representation is lightweight. It captures structure (elements, features, relationships, containment) sufficient for rendering. It does NOT implement the full KerML metamodel. Semantic analysis is delegated to the validator.

3. Parsing is structural, not semantic. The parser extracts element kinds, names, types, features, and nesting from .sysml text. It does not resolve references, check types, or validate semantics.

4. Validation is external. On native, call validate-sysml as a subprocess. On web, call the backend validation API. Parse GNU-format output (file:line:col: severity: message). Never reimplement validation logic.

5. Rendering follows the specification. Consult the GBNF in subclause 8.2.3 of formal/25-09-03 and the graphical notation intro PDF for rendering rules. When in doubt, check what SysON does.

6. Same rendering code for all platforms. The render/ module must not contain platform-specific code. All platform differences live in platform/.

Spec Conformance Invariant

Compliance with the OMG SysML v2 graphical notation specification (formal/25-09-03) is an invariant of this project. No change may violate the specification. Specifically:

• Corner radii: DEFINITION_CORNER_RADIUS (0.0) for definitions and packages; USAGE_CORNER_RADIUS (6.0) for usages. This applies at every LOD level and in every rendering path (full, compact, label, dot, overview).
• Named constants only: every numeric value in src/render/ that controls drawing (stroke widths, font scales, spacing, sizes) must reference a named constant in theme.rs. No bare magic numbers in rendering code.
• All stroke widths named: every Stroke::new() call in rendering code must use a theme:: constant for its width argument.
• Keyword format: keywords are lowercase text rendered inside << >> guillemets.
• Port geometry: ports are PORT_SIZE x PORT_SIZE squares with CornerRadius::ZERO, centered on the parent element boundary.
• Frame geometry: frames use CornerRadius::ZERO with the tab anchored at the top-left corner.
• Connector styles: flow connectors have filled arrowheads; bind and allocate connectors are dashed; each relationship kind has a distinct color.

These rules are enforced by tests/spec_conformance.rs. That test suite must pass before any change is merged. When adding new rendering code, add corresponding spec conformance tests.

Coding Conventions

Rust Style

• Edition 2024. Use current idioms.
• cargo clippy must pass with no warnings.
• Prefer &str over String in function signatures where possible.
• Use thiserror for error types, not string errors.
• No unwrap() in library code. unwrap() is acceptable only in tests and in main() for fatal setup errors.
• Keep functions short. Extract when a function exceeds ~40 lines.
• Minimize pub surface. Default to private; expose only what panels and renderer need.

Cross-Platform Rules

• Use #[cfg(not(target_arch = "wasm32"))] for native-only code.
• Use #[cfg(target_arch = "wasm32")] for web-only code.
• Never use std::fs, std::process, std::net, or notify in code that compiles for WASM. These do not exist on wasm32.
• The model/, render/, and panels/ modules must be platform-agnostic. Only platform/, validator.rs, and watcher.rs may use cfg gates.

egui Conventions

• Use the glow backend. Feature flags: eframe = { default-features = false, features = ["glow"] }
• For WASM builds, eframe automatically uses WebGL via glow.
• Use egui::Painter for all diagram rendering. Do not drop to raw OpenGL/WebGL unless absolutely necessary.
• Panels use egui::SidePanel, egui::TopBottomPanel, egui::CentralPanel. Use egui_tiles for user-rearrangeable docking.
• Immediate mode: compute layout and draw every frame. Cache expensive computations (parsing, layout) but not draw calls.
• Colors and sizes should be defined as constants in a theme module, not hardcoded in rendering code.

SysML v2 Rendering Constants

These rendering rules come from the specification:

// Corner radius for usage elements (definitions use radius 0.0)
const USAGE_CORNER_RADIUS: f32 = 6.0;

// Port size (small square straddling element boundary)
const PORT_SIZE: f32 = 12.0;

// Compartment separator line
const COMPARTMENT_LINE_WIDTH: f32 = 1.0;

// Connector line widths
const CONNECTOR_LINE_WIDTH: f32 = 1.5;
const CONNECTOR_DASH_LENGTH: f32 = 6.0;
const CONNECTOR_DASH_GAP: f32 = 4.0;

Connector Routing Design Principles

Seven principles govern connector routing. All routing distances reference ROUTE_* constants in theme.rs. Zero magic numbers in layout.rs.

1. Frame encompasses all content. The bounding box includes elements, ports, AND connector waypoints. Layout::content_bounds() is the single source of truth for frame sizing.

2. Dedicated routing corridors. Explicit space between the frame edge and the element field is reserved for connector detours. Elements start at FRAME_PADDING + ROUTE_FRAME_MARGIN vertically and FRAME_PADDING + ROUTE_FRAME_MARGIN + ROUTE_COLUMN_GAP_MARGIN horizontally.

3. Minimum clearances. Routes maintain ROUTE_ELEMENT_CLEARANCE (20px) from element edges and ROUTE_FRAME_MARGIN (30px) from the frame edge. Based on professional tool standards (yEd, draw.io, Visio).

4. Named constants only. Every routing distance references a ROUTE_* constant. The constants and their values:

   ROUTE_STUB_LENGTH       = 20.0  // port exit before first bend
   ROUTE_ELEMENT_CLEARANCE = 20.0  // min gap from route to element
   ROUTE_PARALLEL_SPACING  =  8.0  // min y-separation for overlapping h-segments
   ROUTE_FRAME_MARGIN      = 30.0  // min distance from route to frame edge
   ROUTE_CHANNEL_SPREAD    =  8.0  // x-offset between parallel vertical channels
   ROUTE_COLUMN_MERGE      = 10.0  // threshold for merging adjacent columns
   ROUTE_COLUMN_GAP_MARGIN = 25.0  // margin outside first/last column
   ROUTE_EDGE_TOLERANCE    =  2.0  // threshold for matching point to edge
   ROUTE_BOUNDARY_MARGIN   =  1.0  // inset for crossing checks

5. Parallel deconfliction. Horizontal segments from different connectors that overlap in x are offset by ROUTE_PARALLEL_SPACING (8px, derived from PCB 3W rule: >=3x the 1.5px connector line width plus margin). Implemented via deconflict_y() which tracks used_h_levels across all routed connectors.

6. Drawing order. Connectors drawn BEFORE elements. Element fill rectangles visually occlude lines that pass through element areas. This is industry standard in yEd, Visio, and draw.io.

7. Visual hierarchy. Connector stroke (1.5px, colored per relationship type) is distinct from frame stroke (2.0px, dark blue-gray). Never confusable.

External Tool Integration

validate-sysml (native mode)

validate-sysml path/to/file.sysml

• Expects validate-sysml on PATH or at ~/.local/share/sysmlv2-validator/validate-sysml
• Requires Java 21+
• Output: GNU format errors to stderr
• Exit code: 0 = valid, 1 = errors

Validation API (web mode)

The containerized deployment runs validate-sysml server-side. The WASM client posts model content to a REST endpoint and receives diagnostics as JSON. The API contract:

POST /api/validate
Content-Type: text/plain
Body: <.sysml file content>

Response: 200
Content-Type: application/json
Body: [{"file": "...", "line": 1, "col": 1, "severity": "error", "message": "..."}]

File Watching (native mode only)

Watch .sysml files for changes from external editors (Emacs sysml-mode). On change: re-parse, optionally re-validate, update display. Use notify crate. Not available in WASM builds.

SysML v2 Skill

When working on this project with AI assistance, the sysmlv2-skill provides authoritative syntax guidance. Key rules:

• Imports require visibility: private import ScalarValues::*;
• Attribute defs must specialize: attribute def Region :> String;
• Import ScalarValues for basic types (String, Real, Integer, Boolean)
• See ../sysmlv2-skill/references/SYNTAX.md for complete rules

Testing Strategy

• Unit tests: model parsing, rendering geometry calculations, layout algorithms
• Integration tests: parse .sysml files from the SysML v2 Release repository's examples and verify structural extraction
• Visual tests: screenshot comparison (later milestone)
• WASM tests: verify the build compiles and runs under wasm32-unknown-unknown in CI
• Test .sysml files go in tests/fixtures/

Dependencies

Keep dependencies minimal. Justified additions:

Add dependencies only when they provide clear value over a simple implementation. Prefer stdlib solutions. Mark native-only deps with [target.'cfg(not(target_arch = "wasm32"))'.dependencies].