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fix: prevent GeometryOptimizer from merging semicircular arcs into invalid arc

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After splitting a drawing with a circular hole, CadConverterForm writes
the split piece to DXF and re-imports it. The circle (decomposed into
two semicircular arcs by DrawingSplitter) was being incorrectly merged
back into a single zero-sweep arc by GeometryOptimizer.TryJoinArcs
during reimport.

Root cause: TryJoinArcs mutated input arc angles in-place and didn't
guard against merging two arcs that together form a full circle. When
arc2 had startAngle=π, endAngle=0 (DXF wrap-around from 360°→0°), the
mutation produced startAngle=-π, and the merge created an arc with
startAngle=π, endAngle=π (zero sweep), losing half the hole.

Fix: use local variables instead of mutating inputs, require arcs to be
adjacent (endpoints touching) rather than just overlapping, and refuse
to merge when the combined sweep would be a full circle.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
AJ Isaacs
2026-03-25 20:34:38 -04:00
parent 269746b8a4
commit 19001ea5be
2 changed files with 286 additions and 29 deletions
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27
OpenNest.Core/Geometry/GeometryOptimizer.cs
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@@ -133,17 +133,30 @@ namespace OpenNest.Geometry
if (!arc1.Radius.IsEqualTo(arc2.Radius))
return false;
if (arc1.StartAngle > arc1.EndAngle)
arc1.StartAngle -= Angle.TwoPI;
var start1 = arc1.StartAngle;
var end1 = arc1.EndAngle;
var start2 = arc2.StartAngle;
var end2 = arc2.EndAngle;
if (arc2.StartAngle > arc2.EndAngle)
arc2.StartAngle -= Angle.TwoPI;
if (start1 > end1)
start1 -= Angle.TwoPI;
if (arc1.EndAngle < arc2.StartAngle || arc1.StartAngle > arc2.EndAngle)
if (start2 > end2)
start2 -= Angle.TwoPI;
// Check that arcs are adjacent (endpoints touch), not overlapping
var touch1 = end1.IsEqualTo(start2) || (end1 + Angle.TwoPI).IsEqualTo(start2);
var touch2 = end2.IsEqualTo(start1) || (end2 + Angle.TwoPI).IsEqualTo(start1);
if (!touch1 && !touch2)
return false;
var startAngle = arc1.StartAngle < arc2.StartAngle ? arc1.StartAngle : arc2.StartAngle;
var endAngle = arc1.EndAngle > arc2.EndAngle ? arc1.EndAngle : arc2.EndAngle;
var startAngle = start1 < start2 ? start1 : start2;
var endAngle = end1 > end2 ? end1 : end2;
// Don't merge if the result would be a full circle (start == end)
var sweep = endAngle - startAngle;
if (sweep >= Angle.TwoPI - Tolerance.Epsilon)
return false;
if (startAngle < 0) startAngle += Angle.TwoPI;
if (endAngle < 0) endAngle += Angle.TwoPI;