From 3eae8c34f66085f16d35f72f46a60e866853593d Mon Sep 17 00:00:00 2001
From: Mateusz Sych <151755914+SychPL@users.noreply.github.com>
Date: Sat, 17 Oct 2026 10:08:39 +0200
Subject: [PATCH] Fillet beside a hole: the suggested largest radius fits
 (#324) (#1885)

Thanks @SychPL.
---
 crates/kernel/src/blend_fit.rs       | 15 +++++++----
 crates/kernel/src/issue_324_tests.rs | 37 ++++++++++++++++++++++++++++
 crates/kernel/src/lib.rs             |  2 ++
 3 files changed, 49 insertions(+), 5 deletions(-)
 create mode 100644 crates/kernel/src/issue_324_tests.rs

diff --git a/crates/kernel/src/blend_fit.rs b/crates/kernel/src/blend_fit.rs
index 8deb9063..e0c7a351 100644
--- a/crates/kernel/src/blend_fit.rs
+++ b/crates/kernel/src/blend_fit.rs
@@ -360,11 +360,14 @@ enum Clash {
     Blend,
 }
 
-fn first_clash(sel: &Selection, size: Size) -> Option<Clash> {
+/// What a blend at `size` runs into first, if anything. Curved faces are meshed to within the
+/// chord: they count when their mesh reaches into a wedge by more than twice the chord, or, when
+/// `strict`, when it comes within the chord of one (the surface may then be inside it).
+fn first_clash(sel: &Selection, size: Size, strict: bool) -> Option<Clash> {
     let wedges: Vec<Option<Wedge>> = sel.frames.iter().map(|f| f.as_ref().and_then(|f| f.wedge(size))).collect();
     // Planar faces are exact in the mesh; curved ones are within the chord.
     let flat = (sel.size * 1e-7).max(1e-9);
-    let curved = sel.chord * 2.0;
+    let curved = if strict { -sel.chord } else { sel.chord * 2.0 };
     // Planar faces beside an edge lie in its wedge's side planes: outside it means further.
     let out = (sel.size * 1e-6).max(1e-8);
     for (i, (f, w)) in sel.frames.iter().zip(&wedges).enumerate() {
@@ -433,8 +436,10 @@ fn misfit_in(sel: &Selection, size: Size) -> Result<Option<(Clash, Option<f64>)>
     if sel.frames.iter().all(Option::is_none) || !size.value().is_finite() || size.value() <= 0.0 {
         return Ok(None);
     }
-    let Some(clash) = first_clash(sel, size) else { return Ok(None) };
-    // Bisection on the size's steps: `hi` doesn't fit, `lo` does (or is 0).
+    let Some(clash) = first_clash(sel, size, false) else { return Ok(None) };
+    // Bisection on the size's steps: `hi` doesn't fit, `lo` does (or is 0). Strictly: a size
+    // offered as fitting must fit, though a curved face that only touches the wedge at it would
+    // not be refused (a hole whose rim the round's band just reaches, #324).
     let asked = size.value();
     let q = step(asked);
     let (mut lo, mut hi) = (0u64, (asked / q).ceil() as u64);
@@ -443,7 +448,7 @@ fn misfit_in(sel: &Selection, size: Size) -> Result<Option<(Clash, Option<f64>)>
             break;
         }
         let mid = lo + (hi - lo) / 2;
-        if first_clash(sel, size.scaled(mid as f64 * q / asked)).is_none() {
+        if first_clash(sel, size.scaled(mid as f64 * q / asked), true).is_none() {
             lo = mid;
         } else {
             hi = mid;
diff --git a/crates/kernel/src/issue_324_tests.rs b/crates/kernel/src/issue_324_tests.rs
new file mode 100644
index 00000000..57cb86a5
--- /dev/null
+++ b/crates/kernel/src/issue_324_tests.rs
@@ -0,0 +1,37 @@
+//! #324: a round on a block's top edge that would overlap a through hole is refused, and the
+//! largest radius the refusal offers fits.
+
+use solidcraft_geom::Vec3;
+
+use crate::{Body, BoolOp, build::box_solid, build::cylinder, ops::boolean};
+
+/// A 40 x 20 x 10 block with a through hole of radius 3 at (20, `y`).
+fn block_with_hole(y: f64) -> Body {
+    let block = box_solid(Vec3::new(0.0, 0.0, 0.0), Vec3::new(40.0, 20.0, 10.0)).unwrap();
+    let hole = cylinder(Vec3::new(20.0, y, -1.0), Vec3::Z, 3.0, 12.0).unwrap();
+    boolean(&block, &hole, BoolOp::Cut).unwrap().unwrap()
+}
+
+/// The round on the top edge at y = 20 covers the top face from y = 20 - r, and the hole's
+/// wall reaches y = 17.5: a radius over 2.5 runs into the hole. The refusal of 4 mm offered
+/// 2.721 mm, which was refused the same way: the curved wall's mesh, with its tolerance, was
+/// first seen inside the round's region 0.22 mm past where the wall really enters it.
+#[test]
+fn the_radius_offered_beside_a_hole_fits() {
+    let b = block_with_hole(14.5);
+    let edge = Vec3::new(10.0, 20.0, 10.0);
+    let m = crate::fillet(&b, &[edge], 4.0).unwrap_err().to_string();
+    let offered: f64 = m
+        .split("the largest radius that fits is ")
+        .nth(1)
+        .and_then(|s| s.split(' ').next())
+        .and_then(|s| s.parse().ok())
+        .unwrap_or_else(|| panic!("no radius offered: {m}"));
+    assert!(offered > 2.0 && offered <= 2.5, "{m}");
+    let r = crate::fillet(&b, &[edge], offered).unwrap();
+    assert!(r.validity().is_empty(), "{:?}", r.validity());
+    // The block, the hole and the round's corner: the round stays clear of the hole.
+    let want = 8000.0 - std::f64::consts::PI * 9.0 * 10.0 - 40.0 * offered * offered * (1.0 - std::f64::consts::FRAC_PI_4);
+    let v = r.volume_at(0.005).unwrap();
+    assert!((v - want).abs() < 0.05, "{v} against {want}");
+}
diff --git a/crates/kernel/src/lib.rs b/crates/kernel/src/lib.rs
index b443effa..b2be9b2f 100644
--- a/crates/kernel/src/lib.rs
+++ b/crates/kernel/src/lib.rs
@@ -56,6 +56,8 @@ mod issue_1038_tests;
 #[cfg(test)]
 mod issue_1080_tests;
 #[cfg(test)]
+mod issue_324_tests;
+#[cfg(test)]
 mod issue_616_tests;
 #[cfg(test)]
 mod issue_674_tests;