Extrude

Transform 2D polygons into 3D geometry by extruding them along a vertical axis

Overview

The extrude operation transforms a 2D polygon into a 3D solid by extending it along a height vector. This creates a prismatic geometry with the original polygon as the base, vertical side faces connecting the base to the top, and a parallel top face.

Function Signature

extrude_polygon_by_buffer_geometry

pub fn extrude_polygon_by_buffer_geometry(geom_buf: BaseGeometry, height: f64) -> Geometry

Extrudes a polygon defined by buffer geometry to create a 3D mesh.

geom_buf · BaseGeometry · required

The base geometry containing the polygon vertices to extrude. Must have at least 3 vertices to form a valid polygon.

height · f64 · required

The extrusion height in the vertical (Y) direction. Positive values extrude upward, negative values extrude downward.

extrude_brep_face

pub fn extrude_brep_face(brep_face: Brep, height: f64) -> Brep

Extrudes a BREP (Boundary Representation) face to create a new BREP object with topological information.

brep_face · Brep · required

The BREP face to extrude. Must contain at least 3 vertices.

height · f64 · required

The extrusion height in the Y direction.

Return Type

Geometry Structure

The extrude_polygon_by_buffer_geometry function returns a Geometry object with:

• vertices: Complete vertex list including both base and top vertices
• edges: All edges forming the bottom face, top face, and vertical connections
• faces: Bottom face, all side faces (one per edge of the original polygon), and top face

Brep Structure

The extrude_brep_face function returns a Brep object with:

• vertices: Vector of Vertex objects with unique IDs and positions
• edges: Vector of Edge objects connecting vertices
• faces: Vector of Face objects containing vertex indices

How It Works

1. Winding Order: The input vertices are sorted to counter-clockwise (CCW) order to ensure consistent face normals
2. Bottom Face: Creates edges and a face from the original polygon vertices
3. Vertical Edges: Generates new vertices offset by the height vector (0, height, 0) and connects them to base vertices
4. Side Faces: Creates quadrilateral faces connecting each edge of the base to the corresponding edge on top
5. Top Face: Constructs the top face with reversed vertex order for correct normal orientation

Code Examples

Basic Extrusion

use opengeometry::{
    geometry::basegeometry::BaseGeometry,
    operations::extrude::extrude_polygon_by_buffer_geometry,
};
use openmaths::Vector3;

// Create a square base polygon
let vertices = vec![
    Vector3::new(0.0, 0.0, 0.0),
    Vector3::new(1.0, 0.0, 0.0),
    Vector3::new(1.0, 0.0, 1.0),
    Vector3::new(0.0, 0.0, 1.0),
];

let base_geom = BaseGeometry::from_vertices(vertices);

// Extrude 2 units upward
let extruded = extrude_polygon_by_buffer_geometry(base_geom, 2.0);

// Result: A rectangular box with base at Y=0 and top at Y=2

Extruding a Triangle

use opengeometry::operations::extrude::extrude_polygon_by_buffer_geometry;
use opengeometry::geometry::basegeometry::BaseGeometry;
use openmaths::Vector3;

// Create a triangular base
let triangle = vec![
    Vector3::new(0.0, 0.0, 0.0),
    Vector3::new(1.0, 0.0, 0.0),
    Vector3::new(0.5, 0.0, 1.0),
];

let base_geom = BaseGeometry::from_vertices(triangle);
let prism = extrude_polygon_by_buffer_geometry(base_geom, 1.5);

// Result: A triangular prism

Using BREP Extrusion

use opengeometry::{
    brep::Brep,
    operations::extrude::extrude_brep_face,
};
use uuid::Uuid;

// Assuming you have a BREP face
let brep_face = create_polygon_brep(); // Your BREP creation logic

// Extrude to create a 3D BREP with topological data
let extruded_brep = extrude_brep_face(brep_face, 3.0);

// Access topological information
println!("Vertices: {}", extruded_brep.get_vertex_count());
println!("Edges: {}", extruded_brep.get_edge_count());
println!("Faces: {}", extruded_brep.get_face_count());

Visual Examples

Input Polygon (Top View):          Extruded Result (3D):
    
    v3────v2                        v7────v6
    │      │                        ╱│    ╱│
    │      │          +height      ╱ │   ╱ │
    v0────v1          ────────>   v4─┼─v5  │
                                   │ v3──┼─v2
                                   │╱    │╱
                                   v0────v1

Implementation Details

Source Location

~/workspace/source/main/opengeometry/src/operations/extrude.rs:9

Edge Cases

• Minimum Vertices: Polygons with fewer than 3 vertices are technically invalid, but the function proceeds (returns incomplete geometry)
• Direction: Currently extrudes only in the Y direction; future versions may support arbitrary extrusion vectors
• Winding Order: Automatically corrects to CCW to ensure proper face orientation

See Also

• Sweep - Extrude a profile along an arbitrary path
• Offset - Create parallel offset curves
• Triangulate - Convert polygons to triangle meshes