fix: preserve bend lines through drawing split — clip, offset, and carry metadata

DrawingSplitter now clips bend lines to each piece's region using
Liang-Barsky line clipping and offsets them to the new origin. Bend
properties (direction, angle, radius, note text) are preserved through
the entire split pipeline instead of being lost during re-import.

CadConverterForm applies the same origin offset to bends before passing
them to the splitter, and creates FileListItems directly from split
results to avoid re-detection overwriting the bend metadata.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Core/Splitting/DrawingSplitter.cs

@@ -47,7 +47,7 @@ public static class DrawingSplitter
             allEntities.AddRange(pieceEntities);
             allEntities.AddRange(cutoutEntities);
 
-            var piece = BuildPieceDrawing(drawing, allEntities, pieceIndex);
+            var piece = BuildPieceDrawing(drawing, allEntities, pieceIndex, region);
             results.Add(piece);
             pieceIndex++;
         }
@@ -80,7 +80,7 @@ public static class DrawingSplitter
         return entities;
     }
 
-    private static Drawing BuildPieceDrawing(Drawing source, List<Entity> entities, int pieceIndex)
+    private static Drawing BuildPieceDrawing(Drawing source, List<Entity> entities, int pieceIndex, Box region)
     {
         var pieceBounds = entities.Select(e => e.BoundingBox).ToList().GetBoundingBox();
         var offsetX = -pieceBounds.X;
@@ -98,9 +98,69 @@ public static class DrawingSplitter
         piece.Customer = source.Customer;
         piece.Source = source.Source;
         piece.Quantity.Required = source.Quantity.Required;
+
+        if (source.Bends != null && source.Bends.Count > 0)
+        {
+            piece.Bends = new List<Bending.Bend>();
+            foreach (var bend in source.Bends)
+            {
+                var clipped = ClipLineToBox(bend.StartPoint, bend.EndPoint, region);
+                if (clipped == null)
+                    continue;
+
+                piece.Bends.Add(new Bending.Bend
+                {
+                    StartPoint = new Vector(clipped.Value.Start.X + offsetX, clipped.Value.Start.Y + offsetY),
+                    EndPoint = new Vector(clipped.Value.End.X + offsetX, clipped.Value.End.Y + offsetY),
+                    Direction = bend.Direction,
+                    Angle = bend.Angle,
+                    Radius = bend.Radius,
+                    NoteText = bend.NoteText,
+                });
+            }
+        }
+
         return piece;
     }
 
+    /// <summary>
+    /// Clips a line segment to an axis-aligned box using Liang-Barsky algorithm.
+    /// Returns the clipped start/end or null if the line is entirely outside.
+    /// </summary>
+    private static (Vector Start, Vector End)? ClipLineToBox(Vector start, Vector end, Box box)
+    {
+        var dx = end.X - start.X;
+        var dy = end.Y - start.Y;
+        double t0 = 0, t1 = 1;
+
+        double[] p = { -dx, dx, -dy, dy };
+        double[] q = { start.X - box.Left, box.Right - start.X, start.Y - box.Bottom, box.Top - start.Y };
+
+        for (var i = 0; i < 4; i++)
+        {
+            if (System.Math.Abs(p[i]) < Math.Tolerance.Epsilon)
+            {
+                if (q[i] < -Math.Tolerance.Epsilon)
+                    return null;
+            }
+            else
+            {
+                var t = q[i] / p[i];
+                if (p[i] < 0)
+                    t0 = System.Math.Max(t0, t);
+                else
+                    t1 = System.Math.Min(t1, t);
+
+                if (t0 > t1)
+                    return null;
+            }
+        }
+
+        var clippedStart = new Vector(start.X + t0 * dx, start.Y + t0 * dy);
+        var clippedEnd = new Vector(start.X + t1 * dx, start.Y + t1 * dy);
+        return (clippedStart, clippedEnd);
+    }
+
     private static void DecomposeCircles(ShapeProfile profile)
     {
         DecomposeCirclesInShape(profile.Perimeter);

OpenNest.IO/Bending/SolidWorksBendDetector.cs

@@ -24,6 +24,10 @@ namespace OpenNest.IO.Bending
             @"\\[fHCTQWASpOoLlKk][^;]*;|\\P|[{}]|%%[dDpPcC]",
             RegexOptions.Compiled);
 
+        private static readonly Regex UnicodeEscapeRegex = new Regex(
+            @"\\U\+([0-9A-Fa-f]{4})",
+            RegexOptions.Compiled);
+
         public List<Bend> DetectBends(CadDocument document)
         {
             var bendLines = FindBendLines(document);
@@ -116,8 +120,15 @@ namespace OpenNest.IO.Bending
             if (string.IsNullOrEmpty(text))
                 return text;
 
+            // Convert \U+XXXX DXF unicode escapes to actual characters
+            var result = UnicodeEscapeRegex.Replace(text, m =>
+            {
+                var codePoint = int.Parse(m.Groups[1].Value, NumberStyles.HexNumber, CultureInfo.InvariantCulture);
+                return char.ConvertFromUtf32(codePoint);
+            });
+
             // Replace known DXF special characters
-            var result = text
+            result = result
                 .Replace("%%d", "°").Replace("%%D", "°")
                 .Replace("%%p", "±").Replace("%%P", "±")
                 .Replace("%%c", "⌀").Replace("%%C", "⌀");

OpenNest.Tests/Bending/SolidWorksBendDetectorTests.cs

@@ -1,3 +1,4 @@
+using ACadSharp.IO;
 using OpenNest.Bending;
 using OpenNest.IO.Bending;
 
@@ -27,4 +28,27 @@ public class SolidWorksBendDetectorTests
         var bends = BendDetectorRegistry.AutoDetect(doc);
         Assert.Empty(bends);
     }
+
+    [Fact]
+    public void DetectBends_RealDxf_ParsesNotesCorrectly()
+    {
+        var path = Path.Combine(AppContext.BaseDirectory, "Bending", "TestData", "4526 A14 PT45.dxf");
+        Assert.True(File.Exists(path), $"Test DXF not found: {path}");
+
+        using var reader = new DxfReader(path);
+        var doc = reader.Read();
+
+        var detector = new SolidWorksBendDetector();
+        var bends = detector.DetectBends(doc);
+
+        Assert.Equal(2, bends.Count);
+
+        foreach (var bend in bends)
+        {
+            Assert.NotNull(bend.NoteText);
+            Assert.Equal(BendDirection.Up, bend.Direction);
+            Assert.Equal(90.0, bend.Angle);
+            Assert.Equal(0.313, bend.Radius);
+        }
+    }
 }

OpenNest.Tests/OpenNest.Tests.csproj

@@ -28,4 +28,10 @@
     <ProjectReference Include="..\OpenNest.Posts.Cincinnati\OpenNest.Posts.Cincinnati.csproj" />
   </ItemGroup>
 
+  <ItemGroup>
+    <Content Include="Bending\TestData\**\*">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
+  </ItemGroup>
+
 </Project>

OpenNest/Forms/CadConverterForm.cs

@@ -231,14 +231,25 @@ namespace OpenNest.Forms
             shape.Cutouts.ForEach(c => drawEntities.AddRange(c.Entities));
 
             var pgm = ConvertGeometry.ToProgram(drawEntities);
+            var originOffset = Vector.Zero;
             if (pgm.Codes.Count > 0 && pgm[0].Type == CodeType.RapidMove)
             {
                 var rapid = (RapidMove)pgm[0];
-                pgm.Offset(-rapid.EndPoint);
+                originOffset = rapid.EndPoint;
+                pgm.Offset(-originOffset);
                 pgm.Codes.RemoveAt(0);
             }
 
             var drawing = new Drawing(item.Name, pgm);
+            drawing.Bends = item.Bends.Select(b => new Bend
+            {
+                StartPoint = new Vector(b.StartPoint.X - originOffset.X, b.StartPoint.Y - originOffset.Y),
+                EndPoint = new Vector(b.EndPoint.X - originOffset.X, b.EndPoint.Y - originOffset.Y),
+                Direction = b.Direction,
+                Angle = b.Angle,
+                Radius = b.Radius,
+                NoteText = b.NoteText,
+            }).ToList();
 
             using var form = new SplitDrawingForm(drawing);
             if (form.ShowDialog(this) != DialogResult.OK || form.ResultDrawings?.Count <= 1)
@@ -255,25 +266,41 @@ namespace OpenNest.Forms
             var newItems = new List<string>();
 
             var splitWriter = new SplitDxfWriter();
+            var splitItems = new List<FileListItem>();
 
             for (var i = 0; i < form.ResultDrawings.Count; i++)
             {
                 var splitDrawing = form.ResultDrawings[i];
 
-                // Assign bends from the source item — spatial filtering is a future enhancement
-                splitDrawing.Bends.AddRange(item.Bends);
-
                 var splitName = $"{baseName}-{i + 1}.dxf";
                 var splitPath = GetUniquePath(Path.Combine(writableDir, splitName));
 
                 splitWriter.Write(splitPath, splitDrawing);
                 newItems.Add(splitPath);
+
+                // Re-import geometry but keep bends from the split drawing
+                var importer = new DxfImporter();
+                importer.SplinePrecision = Settings.Default.ImportSplinePrecision;
+                var result = importer.Import(splitPath);
+
+                var splitItem = new FileListItem
+                {
+                    Name = Path.GetFileNameWithoutExtension(splitPath),
+                    Entities = result.Entities,
+                    Path = splitPath,
+                    Quantity = item.Quantity,
+                    Customer = item.Customer,
+                    Bends = splitDrawing.Bends ?? new List<Bend>(),
+                    Bounds = result.Entities.GetBoundingBox(),
+                    EntityCount = result.Entities.Count
+                };
+                splitItems.Add(splitItem);
             }
 
-            // Remove original and add split files
+            // Remove original and add split items directly (preserving bend info)
             fileList.RemoveAt(index);
-            foreach (var path in newItems)
-                AddFile(path);
+            foreach (var splitItem in splitItems)
+                fileList.AddItem(splitItem);
 
             if (writableDir != sourceDir)
                 MessageBox.Show($"Split files written to: {writableDir}", "Split Output",