csgrs

A Constructive Solid Geometry (CSG) library in Rust, built around Boolean operations (union, difference, intersection) on sets of polygons stored in BSP trees. csgrs helps you construct 2D and 3D geometry with an OpenSCAD-like syntax, and to transform, interrogate, and simulate those shapes without leaving Rust.

This library aims to integrate cleanly with the Dimforge ecosystem (e.g., nalgebra, Parry, and Rapier), leverage earclip and cavalier_contours for robust mesh and line processing, be reasonably performant on a wide variety of targets, and provide an extensible, type-safe API.

Getting started

Install the Rust language tools from rustup.rs.

cargo new my_cad_project
cd my_cad_project
cargo add csgrs
cargo add nalgebra // provides Points, Vectors, etc.

Example main.rs

// Alias the library’s generic CSG type with empty metadata:
type CSG = csgrs::csg::CSG<()>;

// Create two shapes:
let cube = CSG::cube(2.0, 2.0, 2.0, None);  // 2×2×2 cube at origin, no metadata
let sphere = CSG::sphere(1.0, 16, 8, None); // sphere of radius=1 at origin, no metadata

// Difference one from the other:
let difference_result = cube.difference(&sphere);

// Write the result as an ASCII STL:
let stl = difference_result.to_stl_ascii("cube_minus_sphere");
std::fs::write("cube_sphere_difference.stl", stl).unwrap();

CSG and Polygon Structures

CSG<S> is the main type. It stores a list of polygons (Vec<Polygon<S>>).
Polygon<S> holds:
- a Vec<Vertex> (positions + normals),
- a bool indicating whether the polyline is open or closed,
- an optional metadata field (Option<S>), and
- a Plane describing the polygon’s orientation in 3D.

CSG<S> provides methods for working with 3D shapes, Polygon<S> provides methods for working with 2D shapes. You can build a CSG<S> from polygons with CSG::from_polygons(...). Some 2D functions are re-exported by CSG<S> for ease of use.

2D Shapes

Helper constructors for 2D shapes in the XY plane:

CSG::square(width: Real, length: Real, metadata: Option<S>)
CSG::circle(radius: Real, segments: usize, metadata: Option<S>)
CSG::polygon_2d(&[[x1,y1],[x2,y2],...], metadata: Option<S>)

let square = CSG::square(1.0, 1.0, None); // 1×1 at origin
let rect = CSG::square(2.0, 4.0, None);
let circle = CSG::circle(1.0, 32, None); // radius=1, 32 segments
let circle2 = CSG::circle(2.0, 64, None);

3D Shapes

Similarly, you can create standard 3D primitives:

CSG::cube(width: Real, length: Real, height: Real, metadata: Option<S>)
CSG::sphere(radius: Real, segments: usize, stacks: usize, metadata: Option<S>)
CSG::cylinder(radius: Real, height: Real, segments: usize, metadata: Option<S>)
CSG::frustrum(radius1: Real, radius2: Real, height: Real, segments: usize, metadata: Option<S>) - Construct a frustum at origin with height and radius1 and radius2
CSG::frustrum_ptp(start: Point3, end: Point3, radius1: Real, radius2: Real, segments: usize, metadata: Option<S>) - Construct a frustum from start to end with radius1 and radius2
CSG::polyhedron(points: &[[Real; 3]], faces: &[Vec<usize>], metadata: Option<S>)

// Unit cube at origin, no metadata
let cube = CSG::cube(1.0, 1.0, 1.0, None);

// Sphere of radius=2 at origin with 32 segments and 16 stacks
let sphere = CSG::sphere(2.0, 32, 16, None);

// Cylinder from radius=1, height=2, 16 slices, and no metadata
let cyl = CSG::cylinder(1.0, 2.0, 16, None);

// Create a custom polyhedron from points and face indices:
let points = &[
    [0.0, 0.0, 0.0],
    [1.0, 0.0, 0.0],
    [1.0, 1.0, 0.0],
    [0.0, 1.0, 0.0],
    [0.5, 0.5, 1.0],
];
let faces = vec![
    vec![0, 1, 2, 3], // base rectangle
    vec![0, 1, 4],    // triangular side
    vec![1, 2, 4],
    vec![2, 3, 4],
    vec![3, 0, 4],
];
let pyramid = CSG::polyhedron(points, &faces, None);

3D Boolean Operations

Three primary operations:

let union_result = cube.union(&sphere);
let difference_result = cube.difference(&sphere);
let intersection_result = cylinder.intersection(&sphere);

They all return a new CSG<S>

Transformations

CSG::translate(vector: Vector3) - Returns the CSG translated by vector
CSG::rotate(x_deg, y_deg, z_deg) - Returns the CSG rotated in x, y, and z
CSG::scale(scale_x, scale_y, scale_z) - Returns the CSG scaled in x, y, and z
CSG::mirror(plane: Plane) - Returns the CSG mirrored across plane
CSG::center() - Returns the CSG centered at the origin
CSG::float() - Returns the CSG translated so that its bottommost point(s) sit exactly at z=0
CSG::transform(&Matrix4) - Returns the CSG after applying arbitrary affine transforms

use nalgebra::Vector3;

let moved = cube.translate(Vector3::new(3.0, 0.0, 0.0));
let rotated = sphere.rotate(0.0, 45.0, 90.0);
let scaled = cylinder.scale(2.0, 1.0, 1.0);
let plane_x = Plane { normal: Vector3::x(), w: 0.0 }; // x=0 plane
let plane_y = Plane { normal: Vector3::y(), w: 0.0 }; // y=0 plane
let plane_z = Plane { normal: Vector3::z(), w: 0.0 }; // z=0 plane
let mirrored = cube.mirror(plane_x);

Extrusions and Revolves

Linear Extrude:
- my_2d_shape.extrude(height: Real)
- my_2d_shape.extrude_vector(direction: Vector3)
- my_2d_shape.linear_extrude(direction: Vector3, twist: Real, segments: usize, scale: Real)

Extrude Between Two Polygons:

let polygon_bottom = CSG::circle(2.0, 64, None);
let polygon_top = polygon_bottom.translate(Vector3::new(0.0, 0.0, 5.0));
let lofted = CSG::extrude_between(&polygon_bottom.polygons[0],
                                    &polygon_top.polygons[0],
                                    false);

Rotate-Extrude (Revolve): my_2d_shape.rotate_extrude(angle_degs, segments)
Sweep: sweep(shape_2d: &Polygon<S>, path_2d: &Polygon<S>)
Extrude a polyline to create a surface: extrude_polyline(poly: &Polyline, direction: Vector3, metadata: Option<S>)

let square = CSG::square(2.0, 2.0, None);
let prism = square.extrude(5.0);

let revolve_shape = square.rotate_extrude(360.0, 16);

Miscellaneous Operations

CSG::inverse() — flips the inside/outside orientation.
CSG::convex_hull() — uses chull to generate a 3D convex hull.
CSG::minkowski_sum(&other) — naive Minkowski sum, then takes the hull.
CSG::ray_intersections(origin, direction) — returns all intersection points and distances.
CSG::flatten() — flattens a 3D shape into 2D (on the XY plane), unions the outlines.
CSG::slice(Some(plane)) — slices the CSG by a plane and returns the cross-section polygons.
CSG::offset_2d(distance) — outward (or inward) offset in 2D using cavalier_contours.
CSG::subdivide_triangles(subdivisions) — subdivides each polygon’s triangles, increasing mesh density.
CSG::renormalize() — re-computes each polygon’s plane from its vertices, resetting all normals.
CSG::reconstruct_polyline_3d(polylines: &[Polygon<S>]) — reconstructs a 3d polyline from 2d polylines with matching start/end points
CSG::bounding_box() — computes the bounding box of the shape
CSG::triangulate() — triangulates all polygons returning a CSG containing triangles
CSG::triangulate_earclip() — triangulates all polygons with earclip returning a CSG containing triangles
CSG::from_polygons(polygons: &[Polygon<S>]) - create a new CSG from Polygons
CSG::from_polylines(polylines: &[Polyline], metadata: Option<S>) — create a new CSG from cavalier_contours polylines
CSG::from_earclip(polys: &[Vec<Vec<Real>>], metadata: Option<S>) — create a new CSG from earclip polys
CSG::from_earcut(polys: &[Vec<Vec<Real>>], metadata: Option<S>) - create a new CSG from earcut polys
CSG::vertices() — collect all vertices from the CSG
CSG::gyroid(resolution: usize, period: Real, iso_value: Real) - Generate a Triply Periodic Minimal Surface (Gyroid) inside the volume of self
CSG::from_image(img: &GrayImage, threshold: u8, closepaths: bool, metadata: Option<S>) - Builds a new CSG from the “on” pixels of a grayscale image

Working with Metadata

CSG<S> is generic over S: Clone. Each polygon has an optional metadata: Option<S>.
Use cases include storing color, ID, or layer info.

use csgrs::polygon::Polygon;
use csgrs::vertex::Vertex;
use nalgebra::{Point3, Vector3};

#[derive(Clone)]
struct MyMetadata {
    color: (u8, u8, u8),
    label: String,
}

type CSG = csgrs::CSG<MyMetadata>;

// For a single polygon:
let mut poly = Polygon::new(
    vec![
        Vertex::new(Point3::new(0.0, 0.0, 0.0), Vector3::z()),
        Vertex::new(Point3::new(1.0, 0.0, 0.0), Vector3::z()),
        Vertex::new(Point3::new(0.0, 1.0, 0.0), Vector3::z()),
    ],
    Some(MyMetadata {
        color: (255, 0, 0),
        label: "Triangle".into(),
    }),
);

// Retrieve metadata
if let Some(data) = poly.metadata() {
    println!("This polygon is labeled {}", data.label);
}

// Mutate metadata
if let Some(data_mut) = poly.metadata_mut() {
    data_mut.label.push_str("_extended");
}

STL

Export ASCII STL: csg.to_stl_ascii("solid_name") -> String
Export Binary STL: csg.to_stl_binary("solid_name") -> io::Result<Vec<u8>>
Import STL: CSG::from_stl(&stl_data) -> io::Result<CSG<S>>

// Save to ASCII STL
let stl_text = csg_union.to_stl_ascii("union_solid");
std::fs::write("union_ascii.stl", stl_text).unwrap();

// Save to binary STL
let stl_bytes = csg_union.to_stl_binary("union_solid").unwrap();
std::fs::write("union_bin.stl", stl_bytes).unwrap();

// Load from an STL file on disk
let file_data = std::fs::read("some_file.stl")?;
let imported_csg = CSG::from_stl(&file_data)?;

DXF

Export: csg.to_dxf() -> Result<Vec<u8>, Box<dyn Error>>
Import: CSG::from_dxf(&dxf_data) -> Result<CSG<S>, Box<dyn Error>>

// Export DXF
let dxf_bytes = csg_obj.to_dxf()?;
std::fs::write("output.dxf", dxf_bytes)?;

// Import DXF
let dxf_data = std::fs::read("some_file.dxf")?;
let csg_dxf = CSG::from_dxf(&dxf_data)?;

TrueType Text

You can generate 2D text geometry in the XY plane from TTF fonts via meshtext:

let font_data = include_bytes!("../fonts/MyFont.ttf");
let csg_text = CSG::text("Hello!", font_data, Some(20.0), None);

// Then extrude the text to make it 3D:
let text_3d = csg_text.extrude(1.0);

Create a Parry `TriMesh`

csg.to_trimesh() returns a SharedShape containing a TriMesh<Real>.

use csgrs::csg::CSG;
use csgrs::float_types::rapier3d::prelude::*;  // re-exported for f32/f64 support

let trimesh_shape = csg_obj.to_trimesh(); // SharedShape with a TriMesh

Create a Rapier Rigid Body

csg.to_rigid_body(rb_set, co_set, translation, rotation, density) helps build and insert both a rigid body and a collider:

use nalgebra::Vector3;
use csgrs::float_types::rapier3d::prelude::*;  // re-exported for f32/f64 support
use csgrs::float_types::FRAC_PI_2;
use csgrs::csg::CSG;

let mut rb_set = RigidBodySet::new();
let mut co_set = ColliderSet::new();

let axis_angle = Vector3::z() * FRAC_PI_2; // 90° around Z
let rb_handle = csg_obj.to_rigid_body(
    &mut rb_set,
    &mut co_set,
    Vector3::new(0.0, 0.0, 0.0), // translation
    axis_angle,                  // axis-angle
    1.0,                         // density
);

Mass Properties

let density = 1.0;
let (mass, com, inertia_frame) = csg_obj.mass_properties(density);
println!("Mass: {}", mass);
println!("Center of Mass: {:?}", com);
println!("Inertia local frame: {:?}", inertia_frame);

Manifold Check

csg.is_manifold() triangulates the CSG, builds a HashMap of all edges (pairs of vertices), and checks that each is used exactly twice. Returns true if manifold, false if not.

if (csg_obj.is_manifold()){
    println!("CSG is manifold!");
} else {
    println!("Not manifold.");
}

2D Subsystem and Polygon‐Level 2D Operations

Although CSG typically focuses on three‐dimensional Boolean operations, this library also provides a robust 2D subsystem built on top of cavalier_contours. Each Polygon<S> in 3D can be projected into 2D (its own local XY plane) for 2D boolean operations such as union, difference, intersection, and xor. These are especially handy if you’re offsetting shapes, working with complex polygons, or just want 2D output.

Below is a quick overview of the 2D‐related methods you’ll find on Polygon<S>:

Polygon::to_2d() and Polygon::from_2d(...)

to_2d()
Projects the polygon from its 3D plane into a 2D Polyline.
Internally:
1. Finds a transform that sends polygon.plane.normal to the +Z axis.
2. Transforms each vertex into that local coordinate system (so the polygon lies at z = 0).
3. Returns a 2D Polyline of (x, y, bulge) points (here, bulge is set to 0.0 by default).
from_2d(polyline)
The inverse of to_2d(), creating a 3D Polygon from a 2D Polyline. This method uses the same plane as the polygon on which you called from_2d(). That is, it takes (x, y) points in the local XY plane of self.plane and lifts them back into 3D space.

These two functions let you cleanly convert between a 3D polygon and a pure 2D representation whenever you need to do 2D manipulations.

Tip: If your polygons truly are already in the global XY plane (i.e., z ≈ 0), or you would like to flatten them without adjusting for their reference plane, you can use Polygon::to_polyline() and Polygon::from_polyline(...). Those skip the plane‐based transform and simply store or read (x, y, 0.0) directly.

2D Boolean Operations

A Polygon<S> supports union, difference, intersection, and xor in 2D. Each of these methods:

Projects both polygons into 2D via to_2d().
Invokes cavalier_contours to compute the boolean operation.
Reconstructs one or more resulting polygons in 3D using from_2d(...).

Each operation returns a Vec<Polygon<S>> rather than a single polygon, because the result may split into multiple disjoint pieces.

Polygon::union(&other) -> Vec<Polygon<S>>
self ∪ other. Merges overlapping or adjacent areas.
Polygon::intersection(&other) -> Vec<Polygon<S>>
self ∩ other. Keeps only overlapping regions.
Polygon::difference(&other) -> Vec<Polygon<S>>
self \ other. Subtracts other from self.
Polygon::xor(&other) -> Vec<Polygon<S>>
Symmetric difference (self ∪ other) \ (self ∩ other)—keeps regions that belong to exactly one polygon.

Example usage:

let p1 = polygon_a.union(&polygon_b);          // 2D union
let p2 = polygon_a.difference(&polygon_b);     // 2D difference
let p3 = polygon_a.intersection(&polygon_b);   // 2D intersection
let p4 = polygon_a.xor(&polygon_b);            // 2D xor

Transformations

Polygon::translate(vector: Vector3) - Returns a new Polygon translated by vector
Polygon::rotate(axis: Vector3, angle: Real, center: Option<Point3>) - Rotates the polygon by a given angle in radians about axis. If a center is provided the rotation is performed about that point, otherwise rotation is about the origin.
Polygon::scale(factor: Real) - Uniformly scales the polygon by the given factor
Polygon::mirror_x() - Mirrors the polygon about the x axis
Polygon::mirror_y() - Mirrors the polygon about the y axis
Polygon::mirror_z() - Mirrors the polygon about the z axis
Polygon::transform(&Matrix4) for arbitrary affine transforms
Polygon::flip() - Reverses winding order, flips vertices normals, and flips the plane normal, i.e. flips the polygon
Polygon::convex_hull() - Returns a new Polygon that is the convex hull of the current polygon’s vertices
Polygon::minkowski_sum(other: Polygon<S>) - Returns the Minkowski sum of this polygon and other

Misc functions

Polygon::subdivide_triangles() - Subdivide this polygon into smaller triangles
Polygon::calculate_new_normal()- return a normal calculated from all polygon vertices
Polygon::set_new_normal() - recalculate and set polygon normal
Polygon::triangulate() - Triangulate this polygon into a list of triangles, each triangle is [v0, v1, v2]
Polygon::offset(distance: Real) - offset a polygon by distance in positive or negative direction depending on normal
Polygon::reconstruct_arcs(min_match: usize, rms_limit: Real, angle_limit_degs: Real, offset_limit: Real) - Attempt to reconstruct arcs of constant radius from this polygon
Polygon::check_coordinates_finite() - Returns an error if any coordinate is not finite (NaN or ±∞)
Polygon::check_repeated_points() - Check for repeated adjacent points. Return the first repeated coordinate if found
Polygon::check_ring_closed() - Check ring closure: first and last vertex must coincide if polygon is meant to be closed
Polygon::check_minimum_ring_size() - Check that the ring has at least 3 distinct points
Polygon::check_ring_self_intersection() - Very basic ring self‐intersection check by naive line–line intersection

Signed Area (Shoelace)

The polyline_area function computes the signed area of a closed Polyline:

Positive if the points are in counterclockwise (CCW) order.
Negative if the points are in clockwise (CW) order.
Near‐zero for degenerate or collinear loops.

Roadmap / Todo

fix up error handling with result types
convert more for loops to iterators
parry, rapier behind feature flags
polygons_by_metadata public function of a CSG
- draft implementation done, pending API discussion
extend flatten to work with arbitrary planes
determine why flattened_cube.stl produces invalid output with to_stl_binary but not to_stl_ascii
determine why square_2d_shrink.stl produces invalid output with to_stl_binary but not to_stl_ascii
determine why square_2d produces invalid output with to_stl_binary but not to_stl_ascii
remaining 2d functions to finalize: signed area, is_ccw, line/line intersection
- tests
bending
document compounded transformations using nalgebra
invert Polygon::open to match cavalier_contours
vector font for machining / svg import/export
- https://github.com/kamalmostafa/hershey-fonts
  - https://github.com/kicad-rs/hershey/blob/main/src/lib.rs
- http://www.ofitselfso.com/MiscNotes/CAMBamStickFonts.php
screw threads
attachment points / rapier integration
implement 2d offsetting with these for testing against cavalier_contours
- https://github.com/Akirami/polygon-offsetting
- https://github.com/anlumo/offset_polygon
support scale and translation along a vector in rotate extrude
investigate marching_cubes, marching_cubes_rs
identify more candidates for par_iter
reimplement 3D offsetting with voxelcsgrs or https://docs.rs/parry3d/latest/parry3d/transformation/vhacd/struct.VHACD.html
reimplement convex hull with https://docs.rs/parry3d-f64/latest/parry3d_f64/transformation/fn.convex_hull.html
implement 2d/3d convex decomposition with https://docs.rs/parry3d-f64/latest/parry3d_f64/transformation/vhacd/struct.VHACD.html
reimplement transformations and shapes with https://docs.rs/parry3d/latest/parry3d/transformation/utils/index.html
evaluate https://github.com/asny/tri-mesh for useful functions
identify blockers for no-std
identify opportunities to use parry2d_f64 and parry3d_f64 modules and functions to simplify and enhance our own
- https://docs.rs/parry2d-f64/latest/parry2d_f64/index.html
- https://docs.rs/parry3d-f64/latest/parry3d_f64/index.html

Todo maybe

implement constant radius arc support in 2d using cavalier_contours, interpolate/tessellate in from_polygons
extend Polygon to allow edges to store bulge like cavalier_contours and update split_polygon to handle line/arc intersections.
https://github.com/PsichiX/density-mesh

License

MIT License

Copyright (c) 2025 Timothy Schmidt

Permission is hereby granted, free of charge, to any person obtaining a copy of this 
software and associated documentation files (the "Software"), to deal in the Software 
without restriction, including without limitation the rights to use, copy, modify, merge, 
publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons 
to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

If you find issues, please file an issue or submit a pull request. Feedback and contributions are welcome!

Have fun building geometry in Rust!

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csgrs

Getting started

Example main.rs

CSG and Polygon Structures

2D Shapes

3D Shapes

3D Boolean Operations

Transformations

Extrusions and Revolves

Miscellaneous Operations

Working with Metadata

STL

DXF

TrueType Text

Create a Parry `TriMesh`

Create a Rapier Rigid Body

Mass Properties

Manifold Check

2D Subsystem and Polygon‐Level 2D Operations

Polygon::to_2d() and Polygon::from_2d(...)

2D Boolean Operations

Transformations

Misc functions

Signed Area (Shoelace)

Roadmap / Todo

Todo maybe

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csgrs

Getting started

Example main.rs

CSG and Polygon Structures

2D Shapes

3D Shapes

3D Boolean Operations

Transformations

Extrusions and Revolves

Miscellaneous Operations

Working with Metadata

STL

DXF

TrueType Text

Create a Parry TriMesh

Create a Rapier Rigid Body

Mass Properties

Manifold Check

2D Subsystem and Polygon‐Level 2D Operations

Polygon::to_2d() and Polygon::from_2d(...)

2D Boolean Operations

Transformations

Misc functions

Signed Area (Shoelace)

Roadmap / Todo

Todo maybe

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Create a Parry `TriMesh`

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