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Build circle-cycle out of multiple arcs

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See the updated documentation for motivation.
This commit is contained in:
Hanno Braun 2024-06-06 19:50:54 +02:00
parent de041b3cca
commit 39b0274a92
1 changed files with 37 additions and 5 deletions
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42
crates/fj-core/src/operations/build/cycle.rs
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@ -1,8 +1,8 @@
use fj_math::{Point, Scalar};
use fj_math::{Point, Scalar, Vector};
use itertools::Itertools;
use crate::{
operations::{build::BuildHalfEdge, update::UpdateCycle},
operations::{build::BuildHalfEdge, insert::Insert, update::UpdateCycle},
storage::Handle,
topology::{Cycle, HalfEdge, Surface},
Core,
@ -19,15 +19,47 @@ pub trait BuildCycle {
Cycle::new([])
}
/// Build a circle
/// # Build a circle
///
/// This circle is built out of 4 distinct arcs.
///
/// ## Implementation Note
///
/// The cycle can't be built out of a single half-edge. That would be
/// invalid although there's not validation check to document and enforce
/// that yet. Please refer to the following issue for more information:
/// <https://github.com/hannobraun/fornjot/issues/2374>
///
/// The cycle is built out of 4 arcs specifically, because that's easier to
/// implement than three, and building it out of two creates geometry that
/// the cycle winding code can't handle right now. The following issue has
/// more information on the cycle winding problems:
/// <https://github.com/hannobraun/fornjot/issues/2130>
fn circle(
center: impl Into<Point<2>>,
radius: impl Into<Scalar>,
surface: Handle<Surface>,
core: &mut Core,
) -> Cycle {
let circle = HalfEdge::circle(center, radius, surface, core);
Cycle::empty().add_half_edges([circle], core)
let center = center.into();
let radius = radius.into();
let radius_right = Vector::from([radius, Scalar::ZERO]);
let radius_up = Vector::from([Scalar::ZERO, radius]);
let a = center + radius_right;
let b = center + radius_up;
let c = center - radius_right;
let d = center - radius_up;
let angle = Scalar::TAU / 4.;
let ab = HalfEdge::arc(a, b, angle, surface.clone(), core).insert(core);
let bc = HalfEdge::arc(b, c, angle, surface.clone(), core).insert(core);
let cd = HalfEdge::arc(c, d, angle, surface.clone(), core).insert(core);
let da = HalfEdge::arc(d, a, angle, surface.clone(), core).insert(core);
Cycle::empty().add_half_edges([ab, bc, cd, da], core)
}
/// Build a polygon