Restore star model

Cargo.toml

@@ -11,6 +11,7 @@ members = [
 
     "models/cuboid",
     "models/spacer",
+    "models/star",
 
     "tools/autolib",
     "tools/automator",

crates/fj-core/src/operations/build/region.rs

@@ -8,6 +8,15 @@ use crate::{
 
 /// Build a [`Region`]
 pub trait BuildRegion {
+    /// Build an empty region
+    fn empty(services: &mut Services) -> Region {
+        let exterior = Cycle::empty().insert(services);
+        let interiors = [];
+        let color = None;
+
+        Region::new(exterior, interiors, color)
+    }
+
     /// Build a circle
     fn circle(
         center: impl Into<Point<2>>,

models/star/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "star"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies.fj]
+path = "../../crates/fj"

models/star/src/lib.rs

@@ -0,0 +1,53 @@
+use std::f64::consts::PI;
+
+use fj::{
+    core::{
+        algorithms::sweep::Sweep,
+        objects::{Cycle, Region, Sketch, Solid},
+        operations::{
+            BuildCycle, BuildRegion, BuildSketch, Insert, Reverse,
+            UpdateRegion, UpdateSketch,
+        },
+        services::Services,
+        storage::Handle,
+    },
+    math::Vector,
+};
+
+pub fn model(num_points: u64, r1: f64, r2: f64, h: f64) -> Handle<Solid> {
+    let mut services = Services::new();
+
+    let num_vertices = num_points * 2;
+    let vertex_iter = (0..num_vertices).map(|i| {
+        let angle_rad = 2. * PI / num_vertices as f64 * i as f64;
+        let radius = if i % 2 == 0 { r1 } else { r2 };
+        (angle_rad, radius)
+    });
+
+    let mut outer_points = Vec::new();
+    let mut inner_points = Vec::new();
+
+    for (angle_rad, radius) in vertex_iter {
+        let (sin, cos) = angle_rad.sin_cos();
+
+        let x = cos * radius;
+        let y = sin * radius;
+
+        outer_points.push([x, y]);
+        inner_points.push([x / 2., y / 2.]);
+    }
+
+    let sketch = Sketch::empty()
+        .add_region(
+            Region::polygon(outer_points, &mut services)
+                .add_interiors([Cycle::polygon(inner_points, &mut services)
+                    .reverse(&mut services)
+                    .insert(&mut services)])
+                .insert(&mut services),
+        )
+        .insert(&mut services);
+
+    let surface = services.objects.surfaces.xy_plane();
+    let path = Vector::from([0., 0., h]);
+    (sketch, surface).sweep(path, &mut services)
+}

models/star/src/main.rs

@@ -0,0 +1,7 @@
+use fj::handle_model;
+
+fn main() -> fj::Result {
+    let model = star::model(5, 1., 2., 1.);
+    handle_model(model)?;
+    Ok(())
+}