From 2c5b7e76fb820b7f6d46d2c64a226ef0952da600 Mon Sep 17 00:00:00 2001
From: Hakan Seven <hakanseven8125@gmail.com>
Date: Mon, 3 Aug 2026 19:45:15 +0300
Subject: [PATCH] fix(acis): complete curved solid faces

Prevent partial sweeps and reversed boundary sampling from dropping surface segments and connector corners.
---
 src/scene/convert/acis_to_truck.rs |  9 ++++++---
 src/scene/convert/solid3d_tess.rs  | 27 +++++++++++++++++----------
 2 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/src/scene/convert/acis_to_truck.rs b/src/scene/convert/acis_to_truck.rs
index fe1e28c1f..3e7f85c3d 100644
--- a/src/scene/convert/acis_to_truck.rs
+++ b/src/scene/convert/acis_to_truck.rs
@@ -374,9 +374,9 @@ fn loop_normal(pts: &[[f64; 3]]) -> [f64; 3] {
 
 // ── Cone / cylinder face ─────────────────────────────────────────────────────
 
-/// Build a cone/cylinder lateral surface as revolution faces. A plain closed
-/// revolution uses the parametric sampler; a pierced one stays here so its
-/// additional boundary loops can trim holes into the curved surface.
+/// Build a pierced cone/cylinder lateral surface as revolution faces. A
+/// single-loop face uses the parametric sampler, avoiding partial revolution
+/// segments that can disappear when the profile crosses a coordinate plane.
 fn cone_faces(
     sat: &SatDocument,
     face: &SatFace,
@@ -411,6 +411,9 @@ fn cone_faces(
     };
 
     let loops = collect_face_loops(sat, face, BOUNDARY_CHORD_FRAC);
+    if loops.len() == 1 {
+        return None;
+    }
     let arcs: Vec<(f64, f64)> = loops
         .iter()
         .map(|lp| cone_boundary_arc(lp, [cx, cy, cz], axis, udir, vdir))
diff --git a/src/scene/convert/solid3d_tess.rs b/src/scene/convert/solid3d_tess.rs
index b37eb7b44..947e27e50 100644
--- a/src/scene/convert/solid3d_tess.rs
+++ b/src/scene/convert/solid3d_tess.rs
@@ -1424,17 +1424,23 @@ pub(crate) fn append_coedge_points(
             // The edge's own sense (relative to its curve) decides the ellipse
             // winding; a reversed edge samples the opposite handedness.
             let reversed = matches!(edge.sense(), Sense::Reversed);
-            let mut sampled = sample_ellipse_arc(
+            // Orient the parameter range before sampling. Reversing an
+            // endpoint-exclusive sample afterwards would drop the traversal
+            // start and retain its end, duplicating the next coedge's point and
+            // cutting the connector corner out of the face boundary.
+            let (start, end) = if fwd {
+                (edge.start_param(), edge.end_param())
+            } else {
+                (edge.end_param(), edge.start_param())
+            };
+            let sampled = sample_ellipse_arc(
                 &ellipse,
-                edge.start_param(),
-                edge.end_param(),
+                start,
+                end,
                 chord_frac,
                 reversed,
             );
             if !sampled.is_empty() {
-                if !fwd {
-                    sampled.reverse();
-                }
                 pts.extend(sampled);
                 return;
             }
@@ -1452,12 +1458,13 @@ pub(crate) fn append_coedge_points(
                 .into_iter()
                 .map(|(x, y, z)| [x, y, z])
                 .collect();
-            // Drop the shared end point so adjacent coedges don't double up.
+            // Orient the inclusive sample first, then drop the traversal end so
+            // the adjacent coedge contributes that shared point.
+            if !fwd {
+                sampled.reverse();
+            }
             sampled.pop();
             if sampled.len() >= 2 {
-                if !fwd {
-                    sampled.reverse();
-                }
                 pts.extend(sampled);
                 return;
             }