Fillet: refuse only crossed faces the round makes, not ones the body had (#1488) (#1517)

Thanks @erkexzcx.

crates/kernel/src/blend.rs

@@ -1121,7 +1121,7 @@ pub fn fillet_g2(body: &Body, edges: &[Vec3], radius: f64) -> Result<Body> {
         let (made, rec) = guard("G2 fillet", || blend_one(&solid, &edge, size, radius, Shape::Curvature))?;
         cur = record::after(record::rebuilt(made, &[&solid], &rec)?, &cur, &counts);
     }
-    closed(cur)
+    closed(body, cur)
 }
 
 /// Most edges whose other orders are tried when the order given is refused.
@@ -1804,9 +1804,16 @@ fn loop_split(cur: &Body, pts: &[Vec3]) -> Result<Option<(Vec<Vec<Vec3>>, Vec<Ve
 /// A fillet's result, refused when a face's boundary crosses itself (#871): rounds that
 /// overlap where a wall is thinner than both leave such faces, which the topology checks
 /// don't see but which show as holes in the model. A fillet either closes the solid or is
-/// refused.
-fn closed(b: Body) -> Result<Body> {
-    match b.crossed_face_loops()? {
+/// refused. Faces of `input` that crossed already and that the fillet carried over unchanged
+/// (a sliver an earlier boolean left far from the rounds, #1488) are not the fillet's doing.
+fn closed(input: &Body, b: Body) -> Result<Body> {
+    let after = b.crossed_faces()?;
+    if after.is_empty() {
+        return Ok(b);
+    }
+    let before = input.crossed_faces()?;
+    let tol = (input.size().max(b.size()) * 1e-6).max(1e-9);
+    match after.iter().filter(|p| !before.iter().any(|q| q.dist(**p) <= tol)).count() {
         0 => Ok(b),
         _ => Err(KernelError::Failed(
             "fillet: the rounds would leave openings in the surface (they overlap where a wall or a face is narrower than both)".into(),
@@ -1832,17 +1839,17 @@ pub fn fillet(body: &Body, edges: &[Vec3], radius: f64) -> Result<Body> {
 fn fillet_built(body: &Body, edges: &[Vec3], radius: f64) -> Result<Body> {
     // Corners the local blends refuse (an earlier round at an edge's end): radius per edge.
     blend(body, edges, radius, Shape::Round, "fillet")
-        .and_then(closed)
+        .and_then(|b| closed(body, b))
         .or_else(|e| {
             let sel: Vec<(Vec3, f64)> = edges.iter().map(|p| (*p, radius)).collect();
             // The local blend's refusal, unless only the corner build found the radius too large.
             crate::blend_corner::fillet_radii(body, &sel)
-                .and_then(closed)
+                .and_then(|b| closed(body, b))
                 .map_err(|e2| keep_size(e, e2))
                 // Three edges at a vertex of any faces end in a sphere.
                 .or_else(|e| {
                     if edges.len() >= 3 {
-                        crate::blend_vertex::fillet_ball_vertices(body, edges, radius).and_then(closed).map_err(|_| e)
+                        crate::blend_vertex::fillet_ball_vertices(body, edges, radius).and_then(|b| closed(body, b)).map_err(|_| e)
                     } else {
                         Err(e)
                     }
@@ -1850,9 +1857,9 @@ fn fillet_built(body: &Body, edges: &[Vec3], radius: f64) -> Result<Body> {
         })
         // Straight edges ending at a curved face that isn't an earlier round's: a rolling ball
         // trimmed by the face. Refused, the refusal above stands.
-        .or_else(|e| blend_with(body, edges, radius, Shape::Round, "fillet", true).and_then(closed).map_err(|_| e))
+        .or_else(|e| blend_with(body, edges, radius, Shape::Round, "fillet", true).and_then(|b| closed(body, b)).map_err(|_| e))
         // Blends meeting at corners on curved faces: all at once.
-        .or_else(|e| corners(body, edges, radius, Shape::Round, "fillet").and_then(closed).map_err(|e2| keep_size(e, e2)))
+        .or_else(|e| corners(body, edges, radius, Shape::Round, "fillet").and_then(|b| closed(body, b)).map_err(|e2| keep_size(e, e2)))
 }
 
 /// The first refusal, unless only the second found the blend too large (a smaller one may fit).
@@ -1970,7 +1977,7 @@ pub fn fillet_each(body: &Body, edges: &[Vec3], radii: &[f64]) -> Result<Body> {
         }
         Ok(b)
     };
-    if let Ok(b) = crate::blend_corner::fillet_radii(body, &sel).and_then(closed).and_then(fit) {
+    if let Ok(b) = crate::blend_corner::fillet_radii(body, &sel).and_then(|b| closed(body, b)).and_then(fit) {
         return Ok(b);
     }
     let mut by_radius: Vec<(f64, Vec<Vec3>)> = Vec::new();

crates/kernel/src/body.rs

@@ -1165,15 +1165,21 @@ impl Body {
     /// (rounds that overlap where a wall is thinner than both, #871). Boundaries that only
     /// touch (at a vertex they share, or within the size's millionth) don't count.
     pub fn crossed_face_loops(&self) -> Result<usize> {
+        Ok(self.crossed_faces()?.len())
+    }
+
+    /// The faces [`Body::crossed_face_loops`] counts, each as the mean of its boundary's
+    /// points: the same for a face an operation carried over unchanged.
+    pub fn crossed_faces(&self) -> Result<Vec<Vec3>> {
         use mt::{BoundedCurve, ParameterDivision1D};
         if self.is_mesh() {
-            return Ok(0);
+            return Ok(Vec::new());
         }
         const MAX_SEGMENTS: usize = 20_000;
         let size = self.size();
         let tol = (size * 1e-6).max(1e-9);
         let chord = (size * 1e-3).max(1e-4);
-        let mut crossed = 0;
+        let mut crossed = Vec::new();
         for f in self.solid.face_iter() {
             let mt::Surface::Plane(pl) = f.oriented_surface() else { continue };
             let o = from_p3(pl.origin());
@@ -1226,7 +1232,10 @@ impl Body {
                 loops.iter().enumerate().flat_map(|(l, segs)| segs.iter().map(move |s| (l, s))).collect();
             let bad = all.iter().enumerate().any(|(i, (_, s))| all.iter().skip(i + 1).any(|(_, t)| cross(s, t)));
             if bad {
-                crossed += 1;
+                let ends: Vec<(f64, f64)> = all.iter().map(|(_, s)| s.0).collect();
+                let k = ends.len().max(1) as f64;
+                let (su, sv) = ends.iter().fold((0.0, 0.0), |acc, p| (acc.0 + p.0, acc.1 + p.1));
+                crossed.push(o + u * (su / k) + v * (sv / k));
             }
         }
         Ok(crossed)