perf: parallelize PairFiller candidates and add GridDedup

- Evaluate pair candidates in parallel batches instead of sequentially
- Add GridDedup to skip duplicate pattern/direction/workArea combos
  across PairFiller and StripeFiller strategies
- Replace crude 30% remnant area estimate with L-shaped geometry
  calculation using actual grid extents and max utilization
- Move FillStrategyRegistry.SetEnabled to outer evaluation loop
  to avoid repeated enable/disable per remnant fill

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

OpenNest.Engine/Fill/GridDedup.cs

@@ -0,0 +1,75 @@
+using System;
+using System.Collections.Concurrent;
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Fill;
+
+/// <summary>
+/// Tracks evaluated grid configurations so duplicate pattern/direction/workArea
+/// combinations can be skipped across fill strategies.
+/// </summary>
+public class GridDedup
+{
+    public const string SharedStateKey = "GridDedup";
+
+    private readonly ConcurrentDictionary<GridKey, byte> _seen = new();
+
+    /// <summary>
+    /// Returns true if this configuration has NOT been seen before (i.e., should be evaluated).
+    /// Returns false if it's a duplicate.
+    /// </summary>
+    public bool TryAdd(Box patternBox, Box workArea, NestDirection dir)
+    {
+        var key = new GridKey(patternBox, workArea, dir);
+        return _seen.TryAdd(key, 0);
+    }
+
+    public int Count => _seen.Count;
+
+    /// <summary>
+    /// Gets or creates a GridDedup from FillContext.SharedState.
+    /// </summary>
+    public static GridDedup GetOrCreate(System.Collections.Generic.Dictionary<string, object> sharedState)
+    {
+        if (sharedState.TryGetValue(SharedStateKey, out var existing))
+            return (GridDedup)existing;
+
+        var dedup = new GridDedup();
+        sharedState[SharedStateKey] = dedup;
+        return dedup;
+    }
+
+    private readonly struct GridKey : IEquatable<GridKey>
+    {
+        private readonly int _patternW, _patternL, _workW, _workL, _dir;
+
+        public GridKey(Box patternBox, Box workArea, NestDirection dir)
+        {
+            _patternW = (int)System.Math.Round(patternBox.Width * 10);
+            _patternL = (int)System.Math.Round(patternBox.Length * 10);
+            _workW = (int)System.Math.Round(workArea.Width * 10);
+            _workL = (int)System.Math.Round(workArea.Length * 10);
+            _dir = (int)dir;
+        }
+
+        public bool Equals(GridKey other) =>
+            _patternW == other._patternW && _patternL == other._patternL &&
+            _workW == other._workW && _workL == other._workL &&
+            _dir == other._dir;
+
+        public override bool Equals(object obj) => obj is GridKey other && Equals(other);
+
+        public override int GetHashCode()
+        {
+            unchecked
+            {
+                var hash = _patternW;
+                hash = hash * 397 ^ _patternL;
+                hash = hash * 397 ^ _workW;
+                hash = hash * 397 ^ _workL;
+                hash = hash * 397 ^ _dir;
+                return hash;
+            }
+        }
+    }
+}

OpenNest.Engine/Fill/PairFiller.cs

@@ -7,6 +7,7 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Threading;
+using System.Threading.Tasks;
 using OpenNest.Engine;
 
 namespace OpenNest.Engine.Fill
@@ -32,13 +33,15 @@ namespace OpenNest.Engine.Fill
         private readonly Size plateSize;
         private readonly double partSpacing;
         private readonly IFillComparer comparer;
+        private readonly GridDedup dedup;
 
-        public PairFiller(Plate plate, IFillComparer comparer = null)
+        public PairFiller(Plate plate, IFillComparer comparer = null, GridDedup dedup = null)
         {
             this.plate = plate;
             this.plateSize = plate.Size;
             this.partSpacing = plate.PartSpacing;
             this.comparer = comparer ?? new DefaultFillComparer();
+            this.dedup = dedup ?? new GridDedup();
         }
 
         public PairFillResult Fill(NestItem item, Box workArea,
@@ -68,20 +71,41 @@ namespace OpenNest.Engine.Fill
             List<Part> best = null;
             var sinceImproved = 0;
             var effectiveWorkArea = workArea;
+            var batchSize = System.Math.Max(2, Environment.ProcessorCount);
 
+            var maxUtilization = candidates.Count > 0 ? candidates.Max(c => c.Utilization) : 1.0;
+            var partBox = drawing.Program.BoundingBox();
+            var partArea = System.Math.Max(partBox.Width * partBox.Length, 1);
+
+            FillStrategyRegistry.SetEnabled("Pairs", "RectBestFit", "Extents", "Linear");
             try
             {
-                for (var i = 0; i < candidates.Count; i++)
+                for (var batchStart = 0; batchStart < candidates.Count; batchStart += batchSize)
                 {
                     token.ThrowIfCancellationRequested();
 
-                    var filled = EvaluateCandidate(candidates[i], drawing, effectiveWorkArea, token);
+                    var batchEnd = System.Math.Min(batchStart + batchSize, candidates.Count);
+                    var batchCount = batchEnd - batchStart;
+                    var batchWorkArea = effectiveWorkArea;
+                    var minCountToBeat = best?.Count ?? 0;
 
-                    if (comparer.IsBetter(filled, best, effectiveWorkArea))
+                    var results = new List<Part>[batchCount];
+                    Parallel.For(0, batchCount,
+                        new ParallelOptions { CancellationToken = token },
+                        j =>
                         {
-                        best = filled;
+                            results[j] = EvaluateCandidate(
+                                candidates[batchStart + j], drawing, batchWorkArea,
+                                minCountToBeat, maxUtilization, partArea, token);
+                        });
+
+                    for (var j = 0; j < batchCount; j++)
+                    {
+                        if (comparer.IsBetter(results[j], best, effectiveWorkArea))
+                        {
+                            best = results[j];
                             sinceImproved = 0;
-                        effectiveWorkArea = TryReduceWorkArea(filled, targetCount, workArea, effectiveWorkArea);
+                            effectiveWorkArea = TryReduceWorkArea(best, targetCount, workArea, effectiveWorkArea);
                         }
                         else
                         {
@@ -94,12 +118,13 @@ namespace OpenNest.Engine.Fill
                             PlateNumber = plateNumber,
                             Parts = best,
                             WorkArea = workArea,
-                        Description = $"Pairs: {i + 1}/{candidates.Count} candidates, best = {best?.Count ?? 0} parts",
+                            Description = $"Pairs: {batchStart + j + 1}/{candidates.Count} candidates, best = {best?.Count ?? 0} parts",
                         });
+                    }
 
-                    if (i + 1 >= EarlyExitMinTried && sinceImproved >= EarlyExitStaleLimit)
+                    if (batchEnd >= EarlyExitMinTried && sinceImproved >= EarlyExitStaleLimit)
                     {
-                        Debug.WriteLine($"[PairFiller] Early exit at {i + 1}/{candidates.Count} — no improvement in last {sinceImproved} candidates");
+                        Debug.WriteLine($"[PairFiller] Early exit at {batchEnd}/{candidates.Count} — no improvement in last {sinceImproved} candidates");
                         break;
                     }
                 }
@@ -108,6 +133,10 @@ namespace OpenNest.Engine.Fill
             {
                 Debug.WriteLine("[PairFiller] Cancelled mid-phase, using results so far");
             }
+            finally
+            {
+                FillStrategyRegistry.SetEnabled(null);
+            }
 
             Debug.WriteLine($"[PairFiller] Best pair result: {best?.Count ?? 0} parts");
             return best ?? new List<Part>();
@@ -151,7 +180,8 @@ namespace OpenNest.Engine.Fill
         }
 
         private List<Part> EvaluateCandidate(BestFitResult candidate, Drawing drawing,
-            Box workArea, CancellationToken token)
+            Box workArea, int minCountToBeat, double maxUtilization, double partArea,
+            CancellationToken token)
         {
             var pairParts = candidate.BuildParts(drawing);
             var angles = BuildTilingAngles(candidate);
@@ -168,6 +198,9 @@ namespace OpenNest.Engine.Fill
                 var engine = new FillLinear(workArea, partSpacing);
                 foreach (var dir in new[] { NestDirection.Horizontal, NestDirection.Vertical })
                 {
+                    if (!dedup.TryAdd(pattern.BoundingBox, workArea, dir))
+                        continue;
+
                     var gridParts = engine.Fill(pattern, dir);
                     if (gridParts != null && gridParts.Count > 0)
                         grids.Add((gridParts, dir));
@@ -180,17 +213,34 @@ namespace OpenNest.Engine.Fill
             // Sort by count descending so we try the best grids first
             grids.Sort((a, b) => b.Parts.Count.CompareTo(a.Parts.Count));
 
+            // Early abort: if the best grid + optimistic remnant can't beat the global best, skip Phase 2
+            if (minCountToBeat > 0)
+            {
+                var topCount = grids[0].Parts.Count;
+                var optimisticRemnant = EstimateRemnantUpperBound(
+                    grids[0].Parts, workArea, maxUtilization, partArea);
+                if (topCount + optimisticRemnant <= minCountToBeat)
+                {
+                    Debug.WriteLine($"[PairFiller] Skipping candidate: grid {topCount} + estimate {optimisticRemnant} <= best {minCountToBeat}");
+                    return null;
+                }
+            }
+
             // Phase 2: try remnant for each grid, skip if grid is too far behind
             List<Part> best = null;
-            var maxRemnantEstimate = EstimateMaxRemnantParts(drawing, workArea);
 
             foreach (var (gridParts, dir) in grids)
             {
                 token.ThrowIfCancellationRequested();
 
                 // If this grid + max possible remnant can't beat current best, skip
-                if (best != null && gridParts.Count + maxRemnantEstimate <= best.Count)
+                if (best != null)
+                {
+                    var remnantBound = EstimateRemnantUpperBound(
+                        gridParts, workArea, maxUtilization, partArea);
+                    if (gridParts.Count + remnantBound <= best.Count)
                         break; // sorted descending, so remaining are even smaller
+                }
 
                 var remnantParts = FillRemnant(gridParts, drawing, workArea, token);
                 List<Part> total;
@@ -212,12 +262,20 @@ namespace OpenNest.Engine.Fill
             return best;
         }
 
-        private static int EstimateMaxRemnantParts(Drawing drawing, Box workArea)
+        private int EstimateRemnantUpperBound(List<Part> gridParts, Box workArea,
+            double maxUtilization, double partArea)
         {
-            var partBox = drawing.Program.BoundingBox();
+            var gridBox = ((IEnumerable<IBoundable>)gridParts).GetBoundingBox();
-            var partArea = System.Math.Max(partBox.Width * partBox.Length, 1);
+
-            var remnantArea = workArea.Area() * 0.3; // remnant is at most ~30% of work area
+            // L-shaped remnant: top strip (full width) + right strip (grid height only)
-            return (int)(remnantArea / partArea) + 1;
+            var topHeight = System.Math.Max(0, workArea.Top - gridBox.Top);
+            var rightWidth = System.Math.Max(0, workArea.Right - gridBox.Right);
+
+            var topArea = workArea.Width * topHeight;
+            var rightArea = rightWidth * System.Math.Min(gridBox.Top - workArea.Y, workArea.Length);
+            var remnantArea = topArea + rightArea;
+
+            return (int)(remnantArea * maxUtilization / partArea) + 1;
         }
 
         private List<Part> FillRemnant(List<Part> gridParts, Drawing drawing,
@@ -263,9 +321,6 @@ namespace OpenNest.Engine.Fill
                 return cachedResult;
             }
 
-            FillStrategyRegistry.SetEnabled("Pairs", "RectBestFit", "Extents", "Linear");
-            try
-            {
             var remnantEngine = NestEngineRegistry.Create(plate);
             var item = new NestItem { Drawing = drawing };
             var parts = remnantEngine.Fill(item, remnantBox, null, token);
@@ -281,11 +336,6 @@ namespace OpenNest.Engine.Fill
 
             return null;
         }
-            finally
-            {
-                FillStrategyRegistry.SetEnabled(null);
-            }
-        }
 
         private static List<double> BuildTilingAngles(BestFitResult candidate)
         {

OpenNest.Engine/Fill/StripeFiller.cs

@@ -20,6 +20,7 @@ public class StripeFiller
     private readonly FillContext _context;
     private readonly NestDirection _primaryAxis;
     private readonly IFillComparer _comparer;
+    private readonly GridDedup _dedup;
 
     /// <summary>
     /// When true, only complete stripes are placed — no partial rows/columns.
@@ -38,6 +39,7 @@ public class StripeFiller
         _context = context;
         _primaryAxis = primaryAxis;
         _comparer = context.Policy?.Comparer ?? new DefaultFillComparer();
+        _dedup = GridDedup.GetOrCreate(context.SharedState);
     }
 
     public List<Part> Fill()
@@ -115,6 +117,10 @@ public class StripeFiller
         var rotatedPattern = FillHelpers.BuildRotatedPattern(pairParts, angle);
         var perpDim = GetDimension(rotatedPattern.BoundingBox, perpAxis);
         var stripeBox = MakeStripeBox(workArea, perpDim, primaryAxis);
+
+        if (!_dedup.TryAdd(rotatedPattern.BoundingBox, workArea, primaryAxis))
+            return null;
+
         var stripeEngine = new FillLinear(stripeBox, spacing);
         var stripeParts = stripeEngine.Fill(rotatedPattern, primaryAxis);
 

OpenNest.Engine/Strategies/PairsFillStrategy.cs

@@ -12,7 +12,8 @@ namespace OpenNest.Engine.Strategies
         public List<Part> Fill(FillContext context)
         {
             var comparer = context.Policy?.Comparer;
-            var filler = new PairFiller(context.Plate, comparer);
+            var dedup = GridDedup.GetOrCreate(context.SharedState);
+            var filler = new PairFiller(context.Plate, comparer, dedup);
             var result = filler.Fill(context.Item, context.WorkArea,
                 context.PlateNumber, context.Token, context.Progress);