From c94beb51a43d5c91ac1e8d382ef5fac574b73b3f Mon Sep 17 00:00:00 2001
From: AJ Isaacs <ajisaacs27@gmail.com>
Date: Mon, 16 Mar 2026 22:49:27 -0400
Subject: [PATCH] feat(engine): try interlocking pair patterns in remainder
 strips

FillLinear now accepts optional RemainderPatterns that are tried in
leftover strips after the main grid fill, improving packing density
when pair patterns fit the narrow residual space.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 OpenNest.Engine/FillLinear.cs | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/OpenNest.Engine/FillLinear.cs b/OpenNest.Engine/FillLinear.cs
index 92e6415..8fe1ef0 100644
--- a/OpenNest.Engine/FillLinear.cs
+++ b/OpenNest.Engine/FillLinear.cs
@@ -19,6 +19,11 @@ namespace OpenNest
         
         public double HalfSpacing => PartSpacing / 2;
 
+        /// <summary>
+        /// Optional multi-part patterns (e.g. interlocking pairs) to try in remainder strips.
+        /// </summary>
+        public List<Pattern> RemainderPatterns { get; set; }
+
         private static Vector MakeOffset(NestDirection direction, double distance)
         {
             return direction == NestDirection.Horizontal
@@ -408,7 +413,30 @@ namespace OpenNest
                 return new List<Part>();
 
             var rotations = BuildRotationSet(seedPattern);
-            return FindBestFill(rotations, remainingStrip);
+            var best = FindBestFill(rotations, remainingStrip);
+
+            if (RemainderPatterns != null)
+            {
+                System.Diagnostics.Debug.WriteLine($"[FillRemainingStrip] Strip: {remainingStrip.Width:F1}x{remainingStrip.Length:F1}, individual best={best?.Count ?? 0}, trying {RemainderPatterns.Count} patterns");
+
+                foreach (var pattern in RemainderPatterns)
+                {
+                    var filler = new FillLinear(remainingStrip, PartSpacing);
+                    var h = filler.Fill(pattern, NestDirection.Horizontal);
+                    var v = filler.Fill(pattern, NestDirection.Vertical);
+
+                    System.Diagnostics.Debug.WriteLine($"[FillRemainingStrip]   Pattern ({pattern.Parts.Count} parts, bbox={pattern.BoundingBox.Width:F1}x{pattern.BoundingBox.Length:F1}): H={h?.Count ?? 0}, V={v?.Count ?? 0}");
+
+                    if (h != null && h.Count > (best?.Count ?? 0))
+                        best = h;
+                    if (v != null && v.Count > (best?.Count ?? 0))
+                        best = v;
+                }
+
+                System.Diagnostics.Debug.WriteLine($"[FillRemainingStrip] Final best={best?.Count ?? 0}");
+            }
+
+            return best ?? new List<Part>();
         }
 
         private static double FindPlacedEdge(List<Part> placedParts, NestDirection tiledAxis)