tess2-rust

A pure Rust port of libtess2 — the SGI tessellation library refactored by Mikko Mononen. This is an exact mathematical 1-to-1 port of the C library, preserving all algorithmic behavior including edge cases. Zero external dependencies. No unsafe code. WASM-compatible.

Try the Interactive Demo — 6 interactive pages running entirely in your browser via WebAssembly.

Crate listing: tess2-rust on crates.io.

Part of the rust-apps suite — a collection of Rust graphics and geometry libraries by Lars Brubaker.

Features

• Polygon Tessellation — tessellate complex polygons into triangles, quads, or boundary contours
• Winding Rules — five rules (Odd, NonZero, Positive, Negative, AbsGeqTwo) for flexible fill control
• Multiple Output Types — triangles, connected polygons of configurable size, and boundary contours
• Edge Flags — per-triangle-vertex edge_flags() output identifying original polygon boundary edges, for analytic edge anti-aliasing (halo strips) without hardware MSAA
• Double Precision — coordinates and sweep predicates run in f64 for rotation-stable topology on near-collinear geometry
• Self-Intersecting Polygons — handles self-intersections, overlapping contours, and degenerate geometry
• C#/libtess2 Conformance — 132/132 lion polygons match MatterCAD's agg-sharp Tesselator topologically (see tests/conformance_vs_csharp.rs)
• No Unsafe Code — zero unsafe blocks in the entire codebase
• Zero Dependencies — no external runtime dependencies
• WASM-Compatible — compiles to WebAssembly for browser-based usage

Interactive Demo

All 6 demo pages run in-browser via WebAssembly with no server-side processing:

Page	Description
Basic Shapes	Triangles, quads, pentagons, and concave shapes — the building blocks of tessellation
Polygon with Hole	Outer/inner contour reversal and hole detection
Winding Rules	All five rules compared on stars, bowties, nested shapes, and overlapping polygons
Output Modes	Triangles, quads, connected polygons, and boundary contours
Shape Gallery	Real-world datasets — dude, tank, spaceship, and more from poly2tri and GLU test suites
Interactive Editor	Draw your own polygons and watch them tessellate in real time

Browse the demos →

Quick Start

Add this to your Cargo.toml:

[dependencies]
tess2-rust = "1.0"

use tess2_rust::{Tessellator, WindingRule, ElementType};

let mut tess = Tessellator::new();
tess.add_contour(&[0.0, 0.0, 1.0, 0.0, 1.0, 1.0, 0.0, 1.0]);
tess.tessellate(WindingRule::Odd, ElementType::Polygons, 3);

let vertices = tess.vertices();
let elements = tess.elements();

Winding Rules

• Odd — Fill regions with odd winding number (like even-odd fill)
• NonZero — Fill regions with non-zero winding number
• Positive — Fill regions with positive winding number
• Negative — Fill regions with negative winding number
• AbsGeqTwo — Fill regions with winding number >= 2 in absolute value

Development

Building & Testing

cargo build
cargo test                    # 138 tests
cargo clippy -- -D warnings

Running the Demo Locally

cd demo
bun install
bun run dev

Then open http://localhost:3000 in your browser.

License

SGI Free Software License B (functionally equivalent to MIT). See LICENSE.

Acknowledgments

• Mikko Mononen — Author of the libtess2 refactoring of the SGI code
• SGI — Original tessellation library from the OpenGL Sample Implementation
• Ported by Lars Brubaker, sponsored by MatterHackers
• Ported using Claude by Anthropic