feat: add WeldGapTabSplit implementation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

OpenNest.Core/Splitting/WeldGapTabSplit.cs

@@ -0,0 +1,82 @@
+using System.Collections.Generic;
+using OpenNest.Geometry;
+
+namespace OpenNest;
+
+/// <summary>
+/// Generates rectangular tabs on one side of the split edge (negative side).
+/// The positive side remains a straight line. Tabs act as weld-gap spacers.
+/// </summary>
+public class WeldGapTabSplit : ISplitFeature
+{
+    public string Name => "Weld-Gap Tabs";
+
+    public SplitFeatureResult GenerateFeatures(SplitLine line, double extentStart, double extentEnd, SplitParameters parameters)
+    {
+        var extent = extentEnd - extentStart;
+        var tabCount = parameters.TabCount;
+        var tabWidth = parameters.TabWidth;
+        var tabHeight = parameters.TabHeight;
+
+        // Evenly space tabs along the split line
+        var spacing = extent / (tabCount + 1);
+
+        var negEntities = new List<Entity>();
+        var isVertical = line.Axis == CutOffAxis.Vertical;
+        var pos = line.Position;
+
+        // Tabs protrude toward the negative side (lower coordinate on the split axis)
+        var tabDir = -1.0;
+
+        var cursor = extentStart;
+
+        for (var i = 0; i < tabCount; i++)
+        {
+            var tabCenter = extentStart + spacing * (i + 1);
+            var tabStart = tabCenter - tabWidth / 2;
+            var tabEnd = tabCenter + tabWidth / 2;
+
+            if (isVertical)
+            {
+                if (tabStart > cursor + OpenNest.Math.Tolerance.Epsilon)
+                    negEntities.Add(new Line(new Vector(pos, cursor), new Vector(pos, tabStart)));
+
+                negEntities.Add(new Line(new Vector(pos, tabStart), new Vector(pos + tabDir * tabHeight, tabStart)));
+                negEntities.Add(new Line(new Vector(pos + tabDir * tabHeight, tabStart), new Vector(pos + tabDir * tabHeight, tabEnd)));
+                negEntities.Add(new Line(new Vector(pos + tabDir * tabHeight, tabEnd), new Vector(pos, tabEnd)));
+            }
+            else
+            {
+                if (tabStart > cursor + OpenNest.Math.Tolerance.Epsilon)
+                    negEntities.Add(new Line(new Vector(cursor, pos), new Vector(tabStart, pos)));
+
+                negEntities.Add(new Line(new Vector(tabStart, pos), new Vector(tabStart, pos + tabDir * tabHeight)));
+                negEntities.Add(new Line(new Vector(tabStart, pos + tabDir * tabHeight), new Vector(tabEnd, pos + tabDir * tabHeight)));
+                negEntities.Add(new Line(new Vector(tabEnd, pos + tabDir * tabHeight), new Vector(tabEnd, pos)));
+            }
+
+            cursor = tabEnd;
+        }
+
+        // Final segment from last tab to extent end
+        if (isVertical)
+        {
+            if (extentEnd > cursor + OpenNest.Math.Tolerance.Epsilon)
+                negEntities.Add(new Line(new Vector(pos, cursor), new Vector(pos, extentEnd)));
+        }
+        else
+        {
+            if (extentEnd > cursor + OpenNest.Math.Tolerance.Epsilon)
+                negEntities.Add(new Line(new Vector(cursor, pos), new Vector(extentEnd, pos)));
+        }
+
+        // Positive side: plain straight line (reversed direction)
+        var posEntities = new List<Entity>();
+        if (isVertical)
+            posEntities.Add(new Line(new Vector(pos, extentEnd), new Vector(pos, extentStart)));
+        else
+            posEntities.Add(new Line(new Vector(extentEnd, pos), new Vector(extentStart, pos)));
+
+        return new SplitFeatureResult(negEntities, posEntities);
+    }
+}

OpenNest.Tests/Splitting/SplitFeatureTests.cs

@@ -1,9 +1,53 @@
+using System.Linq;
 using OpenNest.Geometry;
 
 namespace OpenNest.Tests.Splitting;
 
 public class SplitFeatureTests
 {
+    [Fact]
+    public void WeldGapTabSplit_Vertical_TabsOnNegativeSide()
+    {
+        var feature = new WeldGapTabSplit();
+        var line = new SplitLine(50.0, CutOffAxis.Vertical);
+        var parameters = new SplitParameters
+        {
+            Type = SplitType.WeldGapTabs,
+            TabWidth = 2.0,
+            TabHeight = 0.25,
+            TabCount = 2
+        };
+
+        var result = feature.GenerateFeatures(line, 0.0, 100.0, parameters);
+
+        // Positive side (right): single straight line (no tabs)
+        Assert.Single(result.PositiveSideEdge);
+        Assert.IsType<Line>(result.PositiveSideEdge[0]);
+
+        // Negative side (left): has tab protrusions — more than 1 entity
+        Assert.True(result.NegativeSideEdge.Count > 1);
+
+        // All entities should be lines
+        Assert.All(result.NegativeSideEdge, e => Assert.IsType<Line>(e));
+
+        // First entity starts at extent start, last ends at extent end
+        var first = (Line)result.NegativeSideEdge[0];
+        var last = (Line)result.NegativeSideEdge[^1];
+        Assert.Equal(0.0, first.StartPoint.Y, 6);
+        Assert.Equal(100.0, last.EndPoint.Y, 6);
+
+        // Tabs protrude in the negative-X direction (left of split line)
+        var tabEntities = result.NegativeSideEdge.Cast<Line>().ToList();
+        var minX = tabEntities.Min(l => System.Math.Min(l.StartPoint.X, l.EndPoint.X));
+        Assert.Equal(50.0 - 0.25, minX, 6); // tabHeight = 0.25
+    }
+
+    [Fact]
+    public void WeldGapTabSplit_Name()
+    {
+        Assert.Equal("Weld-Gap Tabs", new WeldGapTabSplit().Name);
+    }
+
     [Fact]
     public void StraightSplit_Vertical_ProducesSingleLineEachSide()
     {