feat: overhaul SplitDrawingForm — EntityView, draggable feature handles, UI fixes

- Replace raw Panel with EntityView (via SplitPreview subclass) for proper
  zoom-to-point, middle-button pan, and double-buffered rendering
- Add draggable handles for tab/spike positions along split lines; positions
  flow through to WeldGapTabSplit and SpikeGrooveSplit via SplitLine.FeaturePositions
- Fix OK/Cancel buttons hidden off-screen by putting them in a bottom-docked panel
- Fix DrawControl not invalidating on resize
- Swap plate Width/Length label order, default edge spacing to 0.5
- Rename tab labels: Tab Width→Tab Length, Tab Height→Weld Gap, default count 2
- Spike depth now calculated (read-only), groove depth means positioning depth
  beyond spike tip (default 0.125), converted to total depth internally
- Set entity layers visible so EntityView renders them

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

OpenNest.Core/Geometry/Intersect.cs

@@ -219,6 +219,14 @@ namespace OpenNest.Geometry
         }
 
         internal static bool Intersects(Line line1, Line line2, out Vector pt)
+        {
+            if (!IntersectsUnbounded(line1, line2, out pt))
+                return false;
+
+            return line1.BoundingBox.Contains(pt) && line2.BoundingBox.Contains(pt);
+        }
+
+        internal static bool IntersectsUnbounded(Line line1, Line line2, out Vector pt)
         {
             var a1 = line1.EndPoint.Y - line1.StartPoint.Y;
             var b1 = line1.StartPoint.X - line1.EndPoint.X;
@@ -240,7 +248,7 @@ namespace OpenNest.Geometry
             var y = (a1 * c2 - a2 * c1) / d;
 
             pt = new Vector(x, y);
-            return line1.BoundingBox.Contains(pt) && line2.BoundingBox.Contains(pt);
+            return true;
         }
 
         internal static bool Intersects(Line line, Shape shape, out List<Vector> pts)

OpenNest.Core/Geometry/Shape.cs

@@ -534,7 +534,7 @@ namespace OpenNest.Geometry
         {
             Vector intersection;
 
-            if (Intersect.Intersects(offsetLine, lastOffsetLine, out intersection))
+            if (Intersect.IntersectsUnbounded(offsetLine, lastOffsetLine, out intersection))
             {
                 offsetLine.StartPoint = intersection;
                 lastOffsetLine.EndPoint = intersection;
@@ -558,6 +558,46 @@ namespace OpenNest.Geometry
             throw new NotImplementedException();
         }
 
+        /// <summary>
+        /// Offsets the shape outward by the given distance, detecting winding direction
+        /// to choose the correct offset side. Falls back to the opposite side if the
+        /// bounding box shrinks (indicating the offset went inward).
+        /// </summary>
+        public Shape OffsetOutward(double distance)
+        {
+            var poly = ToPolygon();
+            var side = poly.Vertices.Count >= 3 && poly.RotationDirection() == RotationType.CW
+                ? OffsetSide.Left
+                : OffsetSide.Right;
+
+            var result = OffsetEntity(distance, side) as Shape;
+
+            if (result == null)
+                return null;
+
+            UpdateBounds();
+            var originalBB = BoundingBox;
+            result.UpdateBounds();
+            var offsetBB = result.BoundingBox;
+
+            if (offsetBB.Width < originalBB.Width || offsetBB.Length < originalBB.Length)
+            {
+                Trace.TraceWarning(
+                    "Shape.OffsetOutward: offset shrank bounding box " +
+                    $"(original={originalBB.Width:F3}x{originalBB.Length:F3}, " +
+                    $"offset={offsetBB.Width:F3}x{offsetBB.Length:F3}). " +
+                    "Retrying with opposite side.");
+
+                var opposite = side == OffsetSide.Left ? OffsetSide.Right : OffsetSide.Left;
+                var retry = OffsetEntity(distance, opposite) as Shape;
+
+                if (retry != null)
+                    result = retry;
+            }
+
+            return result;
+        }
+
         /// <summary>
         /// Gets the closest point on the shape to the given point.
         /// </summary>

OpenNest.Core/PartGeometry.cs

@@ -49,7 +49,7 @@ namespace OpenNest
             {
                 // Add chord tolerance to compensate for inscribed polygon chords
                 // being inside the actual offset arcs.
-                var offsetEntity = shape.OffsetEntity(spacing + chordTolerance, OffsetSide.Left) as Shape;
+                var offsetEntity = shape.OffsetOutward(spacing + chordTolerance);
 
                 if (offsetEntity == null)
                     continue;
@@ -71,7 +71,7 @@ namespace OpenNest
 
             foreach (var shape in shapes)
             {
-                var offsetEntity = shape.OffsetEntity(spacing + chordTolerance, OffsetSide.Left) as Shape;
+                var offsetEntity = shape.OffsetOutward(spacing + chordTolerance);
 
                 if (offsetEntity == null)
                     continue;
@@ -109,7 +109,7 @@ namespace OpenNest
 
             foreach (var shape in shapes)
             {
-                var offsetEntity = shape.OffsetEntity(spacing + chordTolerance, OffsetSide.Left) as Shape;
+                var offsetEntity = shape.OffsetOutward(spacing + chordTolerance);
 
                 if (offsetEntity == null)
                     continue;

OpenNest.Core/Splitting/SpikeGrooveSplit.cs

@@ -26,15 +26,19 @@ public class SpikeGrooveSplit : ISplitFeature
         var isVertical = line.Axis == CutOffAxis.Vertical;
         var pos = line.Position;
 
-        // Place pairs evenly: one near each end, with margin
-        var margin = extent * 0.15;
+        // Use custom positions if provided, otherwise place evenly with margin
         var pairPositions = new List<double>();
-        if (pairCount == 1)
+        if (line.FeaturePositions.Count > 0)
+        {
+            pairPositions.AddRange(line.FeaturePositions);
+        }
+        else if (pairCount == 1)
         {
             pairPositions.Add(extentStart + extent / 2);
         }
         else
         {
+            var margin = extent * 0.15;
             var usable = extent - 2 * margin;
             for (var i = 0; i < pairCount; i++)
                 pairPositions.Add(extentStart + margin + usable * i / (pairCount - 1));

OpenNest.Core/Splitting/SplitLine.cs

@@ -1,3 +1,5 @@
+using System.Collections.Generic;
+
 namespace OpenNest;
 
 /// <summary>
@@ -9,6 +11,13 @@ public class SplitLine
     public double Position { get; }
     public CutOffAxis Axis { get; }
 
+    /// <summary>
+    /// Optional custom center positions for features (tabs/spikes) along the split line.
+    /// Values are absolute coordinates on the perpendicular axis.
+    /// When empty, feature generators use their default even spacing.
+    /// </summary>
+    public List<double> FeaturePositions { get; set; } = new();
+
     public SplitLine(double position, CutOffAxis axis)
     {
         Position = position;

OpenNest.Core/Splitting/WeldGapTabSplit.cs

@@ -18,8 +18,18 @@ public class WeldGapTabSplit : ISplitFeature
         var tabWidth = parameters.TabWidth;
         var tabHeight = parameters.TabHeight;
 
-        // Evenly space tabs along the split line
-        var spacing = extent / (tabCount + 1);
+        // Use custom positions if provided, otherwise evenly space
+        var tabCenters = new List<double>();
+        if (line.FeaturePositions.Count > 0)
+        {
+            tabCenters.AddRange(line.FeaturePositions);
+        }
+        else
+        {
+            var spacing = extent / (tabCount + 1);
+            for (var i = 0; i < tabCount; i++)
+                tabCenters.Add(extentStart + spacing * (i + 1));
+        }
 
         var negEntities = new List<Entity>();
         var isVertical = line.Axis == CutOffAxis.Vertical;
@@ -30,9 +40,9 @@ public class WeldGapTabSplit : ISplitFeature
 
         var cursor = extentStart;
 
-        for (var i = 0; i < tabCount; i++)
+        for (var i = 0; i < tabCenters.Count; i++)
         {
-            var tabCenter = extentStart + spacing * (i + 1);
+            var tabCenter = tabCenters[i];
             var tabStart = tabCenter - tabWidth / 2;
             var tabEnd = tabCenter + tabWidth / 2;
 

OpenNest.Engine/Fill/PartBoundary.cs

@@ -33,7 +33,7 @@ namespace OpenNest.Engine.Fill
 
             if (perimeter != null)
             {
-                var offsetEntity = perimeter.OffsetEntity(spacing, OffsetSide.Left) as Shape;
+                var offsetEntity = perimeter.OffsetOutward(spacing);
 
                 if (offsetEntity != null)
                 {

OpenNest/Controls/DrawControl.cs

@@ -167,6 +167,7 @@ namespace OpenNest.Controls
             origin.Y += (Size.Height - lastSize.Height) * 0.5f;
 
             lastSize = Size;
+            Invalidate();
         }
 
         public float LengthWorldToGui(double length)

OpenNest/Forms/SplitDrawingForm.cs

@@ -4,6 +4,7 @@ using System.Drawing;
 using System.Drawing.Drawing2D;
 using System.Linq;
 using System.Windows.Forms;
+using OpenNest.Controls;
 using OpenNest.Converters;
 using OpenNest.Geometry;
 
@@ -18,13 +19,12 @@ public partial class SplitDrawingForm : Form
     private CutOffAxis _currentAxis = CutOffAxis.Vertical;
     private bool _placingLine;
 
-    // Zoom/pan state
-    private float _zoom = 1f;
-    private PointF _pan;
-    private Point _lastMouse;
-    private bool _panning;
-
-    // Snap threshold in screen pixels
+    // Feature handle drag state
+    private int _dragLineIndex = -1;
+    private int _dragFeatureIndex = -1;
+    private int _hoverLineIndex = -1;
+    private int _hoverFeatureIndex = -1;
+    private const float HandleRadius = 5f;
     private const double SnapThreshold = 5.0;
 
     public List<Drawing> ResultDrawings { get; private set; }
@@ -33,20 +33,20 @@ public partial class SplitDrawingForm : Form
     {
         InitializeComponent();
 
-        // Enable double buffering on the preview panel to reduce flicker
-        typeof(Panel).InvokeMember(
-            "DoubleBuffered",
-            System.Reflection.BindingFlags.SetProperty | System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic,
-            null, pnlPreview, new object[] { true });
-
         _drawing = drawing;
         _drawingEntities = ConvertProgram.ToGeometry(drawing.Program)
             .Where(e => e.Layer != SpecialLayers.Rapid).ToList();
         _drawingBounds = drawing.Program.BoundingBox();
 
+        foreach (var entity in _drawingEntities)
+            entity.Layer.IsVisible = true;
+
+        pnlPreview.Entities = _drawingEntities;
+        pnlPreview.DrawOverlays = PaintOverlays;
+
         Text = $"Split Drawing: {drawing.Name}";
         UpdateUI();
-        FitToView();
+        pnlPreview.ZoomToFit(true);
     }
 
     // --- Split Method Selection ---
@@ -72,7 +72,7 @@ public partial class SplitDrawingForm : Form
             var overhang = GetCurrentParameters().FeatureOverhang;
             var axisIndex = cboSplitAxis.SelectedIndex;
 
-            if (axisIndex == 1) // Vertical Only — split the part width using the plate size
+            if (axisIndex == 1)
             {
                 var usable = System.Math.Min(plateW, plateH) - 2 * spacing - overhang;
                 if (usable > 0)
@@ -86,7 +86,7 @@ public partial class SplitDrawingForm : Form
                     }
                 }
             }
-            else if (axisIndex == 2) // Horizontal Only — split the part height using the plate size
+            else if (axisIndex == 2)
             {
                 var usable = System.Math.Min(plateW, plateH) - 2 * spacing - overhang;
                 if (usable > 0)
@@ -100,7 +100,7 @@ public partial class SplitDrawingForm : Form
                     }
                 }
             }
-            else // Auto — both axes
+            else
             {
                 _splitLines.AddRange(AutoSplitCalculator.FitToPlate(_drawingBounds, plateW, plateH, spacing, overhang));
             }
@@ -112,6 +112,7 @@ public partial class SplitDrawingForm : Form
             _splitLines.AddRange(AutoSplitCalculator.SplitByCount(_drawingBounds, hPieces, vPieces));
         }
 
+        InitializeAllFeaturePositions();
         UpdateUI();
         pnlPreview.Invalidate();
     }
@@ -134,8 +135,30 @@ public partial class SplitDrawingForm : Form
     {
         grpTabParams.Visible = radTabs.Checked;
         grpSpikeParams.Visible = radSpike.Checked;
+        InitializeAllFeaturePositions();
         if (radFitToPlate.Checked)
-            RecalculateAutoSplitLines(); // overhang changed
+            RecalculateAutoSplitLines();
+        pnlPreview.Invalidate();
+    }
+
+    private void UpdateSpikeDepth()
+    {
+        var grooveDepth = (double)nudGrooveDepth.Value;
+        var weldGap = (double)nudSpikeWeldGap.Value;
+        nudSpikeDepth.Value = (decimal)(grooveDepth + weldGap);
+    }
+
+    private void OnSpikeParamChanged(object sender, EventArgs e)
+    {
+        UpdateSpikeDepth();
+        if (radFitToPlate.Checked)
+            RecalculateAutoSplitLines();
+        pnlPreview.Invalidate();
+    }
+
+    private void OnFeatureCountChanged(object sender, EventArgs e)
+    {
+        InitializeAllFeaturePositions();
         pnlPreview.Invalidate();
     }
 
@@ -153,7 +176,7 @@ public partial class SplitDrawingForm : Form
         {
             p.Type = SplitType.SpikeGroove;
             p.SpikeDepth = (double)nudSpikeDepth.Value;
-            p.GrooveDepth = (double)nudGrooveDepth.Value;
+            p.GrooveDepth = p.SpikeDepth + (double)nudGrooveDepth.Value;
             p.SpikeWeldGap = (double)nudSpikeWeldGap.Value;
             p.SpikeAngle = (double)nudSpikeAngle.Value;
             p.SpikePairCount = (int)nudSpikePairCount.Value;
@@ -161,51 +184,162 @@ public partial class SplitDrawingForm : Form
         return p;
     }
 
-    // --- Manual Split Line Placement ---
+    // --- Feature Position Management ---
+
+    private int GetFeatureCount()
+    {
+        if (radTabs.Checked) return (int)nudTabCount.Value;
+        if (radSpike.Checked) return (int)nudSpikePairCount.Value;
+        return 0;
+    }
+
+    private void GetExtent(SplitLine sl, out double start, out double end)
+    {
+        if (sl.Axis == CutOffAxis.Vertical)
+        {
+            start = _drawingBounds.Bottom;
+            end = _drawingBounds.Top;
+        }
+        else
+        {
+            start = _drawingBounds.Left;
+            end = _drawingBounds.Right;
+        }
+    }
+
+    private void InitializeFeaturePositions(SplitLine sl)
+    {
+        var count = GetFeatureCount();
+        GetExtent(sl, out var start, out var end);
+        var extent = end - start;
+
+        sl.FeaturePositions.Clear();
+        if (count <= 0 || extent <= 0) return;
+
+        if (radSpike.Checked)
+        {
+            var margin = extent * 0.15;
+            if (count == 1)
+            {
+                sl.FeaturePositions.Add(start + extent / 2);
+            }
+            else
+            {
+                var usable = extent - 2 * margin;
+                for (var i = 0; i < count; i++)
+                    sl.FeaturePositions.Add(start + margin + usable * i / (count - 1));
+            }
+        }
+        else
+        {
+            var spacing = extent / (count + 1);
+            for (var i = 0; i < count; i++)
+                sl.FeaturePositions.Add(start + spacing * (i + 1));
+        }
+    }
+
+    private void InitializeAllFeaturePositions()
+    {
+        foreach (var sl in _splitLines)
+            InitializeFeaturePositions(sl);
+    }
+
+    // --- Mouse Interaction ---
 
     private void OnPreviewMouseDown(object sender, MouseEventArgs e)
     {
-        if (e.Button == MouseButtons.Left && radManual.Checked && _placingLine)
+        if (e.Button != MouseButtons.Left) return;
+
+        var worldPt = pnlPreview.PointControlToWorld(e.Location);
+
+        // Check for feature handle hit
+        var (lineIdx, featIdx) = HitTestFeatureHandle(worldPt);
+        if (lineIdx >= 0)
         {
-            var pt = ScreenToDrawing(e.Location);
-            var snapped = SnapToMidpoint(pt);
+            _dragLineIndex = lineIdx;
+            _dragFeatureIndex = featIdx;
+            return;
+        }
+
+        // Split line placement
+        if (radManual.Checked && _placingLine)
+        {
+            var snapped = SnapToMidpoint(worldPt);
             var position = _currentAxis == CutOffAxis.Vertical ? snapped.X : snapped.Y;
-            _splitLines.Add(new SplitLine(position, _currentAxis));
+            var sl = new SplitLine(position, _currentAxis);
+            InitializeFeaturePositions(sl);
+            _splitLines.Add(sl);
             UpdateUI();
             pnlPreview.Invalidate();
         }
-        else if (e.Button == MouseButtons.Middle)
-        {
-            _panning = true;
-            _lastMouse = e.Location;
-        }
     }
 
     private void OnPreviewMouseMove(object sender, MouseEventArgs e)
     {
-        if (_panning)
+        var worldPt = pnlPreview.PointControlToWorld(e.Location);
+
+        if (_dragLineIndex >= 0)
         {
-            _pan.X += e.X - _lastMouse.X;
-            _pan.Y += e.Y - _lastMouse.Y;
-            _lastMouse = e.Location;
+            var sl = _splitLines[_dragLineIndex];
+            GetExtent(sl, out var start, out var end);
+            var pos = sl.Axis == CutOffAxis.Vertical ? worldPt.Y : worldPt.X;
+            pos = System.Math.Max(start, System.Math.Min(end, pos));
+            sl.FeaturePositions[_dragFeatureIndex] = pos;
             pnlPreview.Invalidate();
         }
+        else
+        {
+            var (lineIdx, featIdx) = HitTestFeatureHandle(worldPt);
+            if (lineIdx != _hoverLineIndex || featIdx != _hoverFeatureIndex)
+            {
+                _hoverLineIndex = lineIdx;
+                _hoverFeatureIndex = featIdx;
+                pnlPreview.Cursor = _hoverLineIndex >= 0
+                    ? (_splitLines[_hoverLineIndex].Axis == CutOffAxis.Vertical ? Cursors.SizeNS : Cursors.SizeWE)
+                    : Cursors.Cross;
+                pnlPreview.Invalidate();
+            }
+        }
 
-        var drawPt = ScreenToDrawing(e.Location);
-        lblCursor.Text = $"Cursor: {drawPt.X:F2}, {drawPt.Y:F2}";
+        lblCursor.Text = $"Cursor: {worldPt.X:F2}, {worldPt.Y:F2}";
     }
 
     private void OnPreviewMouseUp(object sender, MouseEventArgs e)
     {
-        if (e.Button == MouseButtons.Middle)
-            _panning = false;
+        if (e.Button == MouseButtons.Left && _dragLineIndex >= 0)
+        {
+            _dragLineIndex = -1;
+            _dragFeatureIndex = -1;
+            pnlPreview.Invalidate();
+        }
     }
 
-    private void OnPreviewMouseWheel(object sender, MouseEventArgs e)
+    private (int lineIndex, int featureIndex) HitTestFeatureHandle(Vector worldPt)
     {
-        var factor = e.Delta > 0 ? 1.1f : 0.9f;
-        _zoom *= factor;
-        pnlPreview.Invalidate();
+        if (radStraight.Checked) return (-1, -1);
+
+        var hitRadius = HandleRadius / pnlPreview.ViewScale;
+        for (var li = 0; li < _splitLines.Count; li++)
+        {
+            var sl = _splitLines[li];
+            for (var fi = 0; fi < sl.FeaturePositions.Count; fi++)
+            {
+                var center = GetFeatureHandleWorld(sl, fi);
+                var dx = worldPt.X - center.X;
+                var dy = worldPt.Y - center.Y;
+                if (dx * dx + dy * dy <= hitRadius * hitRadius)
+                    return (li, fi);
+            }
+        }
+        return (-1, -1);
+    }
+
+    private Vector GetFeatureHandleWorld(SplitLine sl, int featureIndex)
+    {
+        var pos = sl.FeaturePositions[featureIndex];
+        return sl.Axis == CutOffAxis.Vertical
+            ? new Vector(sl.Position, pos)
+            : new Vector(pos, sl.Position);
     }
 
     protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
@@ -227,7 +361,7 @@ public partial class SplitDrawingForm : Form
     {
         var midX = _drawingBounds.Center.X;
         var midY = _drawingBounds.Center.Y;
-        var threshold = SnapThreshold / _zoom;
+        var threshold = SnapThreshold / pnlPreview.ViewScale;
 
         if (_currentAxis == CutOffAxis.Vertical && System.Math.Abs(pt.X - midX) < threshold)
             return new Vector(midX, pt.Y);
@@ -236,53 +370,65 @@ public partial class SplitDrawingForm : Form
         return pt;
     }
 
-    // --- Rendering ---
+    // --- Rendering (drawn on top of entities via SplitPreview) ---
 
-    private void OnPreviewPaint(object sender, PaintEventArgs e)
+    private void PaintOverlays(Graphics g)
     {
-        var g = e.Graphics;
         g.SmoothingMode = SmoothingMode.AntiAlias;
-        g.Clear(Color.FromArgb(26, 26, 26));
 
-        g.TranslateTransform(_pan.X, _pan.Y);
-        g.ScaleTransform(_zoom, -_zoom); // flip Y for CNC coordinates
+        // Piece color overlays
+        var regions = BuildPreviewRegions();
+        for (var i = 0; i < regions.Count; i++)
+        {
+            var color = PieceColors[i % PieceColors.Length];
+            using var brush = new SolidBrush(color);
+            var r = regions[i];
+            var tl = pnlPreview.PointWorldToGraph(r.Left, r.Top);
+            var br = pnlPreview.PointWorldToGraph(r.Right, r.Bottom);
+            g.FillRectangle(brush, System.Math.Min(tl.X, br.X), System.Math.Min(tl.Y, br.Y),
+                System.Math.Abs(br.X - tl.X), System.Math.Abs(br.Y - tl.Y));
+        }
 
-        // Draw part outline
-        using var partPen = new Pen(Color.LightGray, 1f / _zoom);
-        DrawEntities(g, _drawingEntities, partPen);
-
-        // Draw split lines
-        using var splitPen = new Pen(Color.FromArgb(255, 82, 82), 1f / _zoom);
+        // Split lines
+        using var splitPen = new Pen(Color.FromArgb(255, 82, 82));
         splitPen.DashStyle = DashStyle.Dash;
         foreach (var sl in _splitLines)
         {
+            PointF p1, p2;
             if (sl.Axis == CutOffAxis.Vertical)
-                g.DrawLine(splitPen, (float)sl.Position, (float)(_drawingBounds.Bottom - 10), (float)sl.Position, (float)(_drawingBounds.Top + 10));
+            {
+                p1 = pnlPreview.PointWorldToGraph(sl.Position, _drawingBounds.Bottom - 10);
+                p2 = pnlPreview.PointWorldToGraph(sl.Position, _drawingBounds.Top + 10);
+            }
             else
-                g.DrawLine(splitPen, (float)(_drawingBounds.Left - 10), (float)sl.Position, (float)(_drawingBounds.Right + 10), (float)sl.Position);
+            {
+                p1 = pnlPreview.PointWorldToGraph(_drawingBounds.Left - 10, sl.Position);
+                p2 = pnlPreview.PointWorldToGraph(_drawingBounds.Right + 10, sl.Position);
+            }
+            g.DrawLine(splitPen, p1, p2);
         }
 
-        // Draw piece color overlays
-        DrawPieceOverlays(g);
-    }
-
-    private void DrawEntities(Graphics g, List<Entity> entities, Pen pen)
-    {
-        foreach (var entity in entities)
+        // Feature position handles
+        if (!radStraight.Checked)
         {
-            if (entity is Line line)
-                g.DrawLine(pen, (float)line.StartPoint.X, (float)line.StartPoint.Y, (float)line.EndPoint.X, (float)line.EndPoint.Y);
-            else if (entity is Arc arc)
+            for (var li = 0; li < _splitLines.Count; li++)
             {
-                var rect = new RectangleF(
-                    (float)(arc.Center.X - arc.Radius),
-                    (float)(arc.Center.Y - arc.Radius),
-                    (float)(arc.Radius * 2),
-                    (float)(arc.Radius * 2));
-                var startDeg = (float)OpenNest.Math.Angle.ToDegrees(arc.StartAngle);
-                var sweepDeg = (float)OpenNest.Math.Angle.ToDegrees(arc.EndAngle - arc.StartAngle);
-                if (rect.Width > 0 && rect.Height > 0)
-                    g.DrawArc(pen, rect, startDeg, sweepDeg);
+                var sl = _splitLines[li];
+                for (var fi = 0; fi < sl.FeaturePositions.Count; fi++)
+                {
+                    var center = pnlPreview.PointWorldToGraph(GetFeatureHandleWorld(sl, fi));
+                    var isDrag = li == _dragLineIndex && fi == _dragFeatureIndex;
+                    var isHover = li == _hoverLineIndex && fi == _hoverFeatureIndex;
+                    var fillColor = isDrag ? Color.FromArgb(255, 82, 82)
+                                  : isHover ? Color.FromArgb(255, 183, 77)
+                                  : Color.White;
+                    using var fill = new SolidBrush(fillColor);
+                    using var border = new Pen(Color.FromArgb(80, 80, 80));
+                    g.FillEllipse(fill, center.X - HandleRadius, center.Y - HandleRadius,
+                        HandleRadius * 2, HandleRadius * 2);
+                    g.DrawEllipse(border, center.X - HandleRadius, center.Y - HandleRadius,
+                        HandleRadius * 2, HandleRadius * 2);
+                }
             }
         }
     }
@@ -297,19 +443,6 @@ public partial class SplitDrawingForm : Form
         Color.FromArgb(40, 128, 222, 234)
     };
 
-    private void DrawPieceOverlays(Graphics g)
-    {
-        // Simple region overlay based on split lines and bounding box
-        var regions = BuildPreviewRegions();
-        for (var i = 0; i < regions.Count; i++)
-        {
-            var color = PieceColors[i % PieceColors.Length];
-            using var brush = new SolidBrush(color);
-            var r = regions[i];
-            g.FillRectangle(brush, (float)r.Left, (float)r.Bottom, (float)r.Width, (float)r.Length);
-        }
-    }
-
     private List<Box> BuildPreviewRegions()
     {
         var verticals = _splitLines.Where(l => l.Axis == CutOffAxis.Vertical).OrderBy(l => l.Position).ToList();
@@ -331,27 +464,6 @@ public partial class SplitDrawingForm : Form
         return regions;
     }
 
-    // --- Coordinate transforms ---
-
-    private Vector ScreenToDrawing(Point screen)
-    {
-        var x = (screen.X - _pan.X) / _zoom;
-        var y = -(screen.Y - _pan.Y) / _zoom; // flip Y
-        return new Vector(x, y);
-    }
-
-    private void FitToView()
-    {
-        if (_drawingBounds.Width <= 0 || _drawingBounds.Length <= 0) return;
-        var pad = 40f;
-        var scaleX = (pnlPreview.Width - pad * 2) / (float)_drawingBounds.Width;
-        var scaleY = (pnlPreview.Height - pad * 2) / (float)_drawingBounds.Length;
-        _zoom = System.Math.Min(scaleX, scaleY);
-        _pan = new PointF(
-            pad - (float)_drawingBounds.Left * _zoom,
-            pnlPreview.Height - pad + (float)_drawingBounds.Bottom * _zoom);
-    }
-
     // --- OK/Cancel ---
 
     private void OnOK(object sender, EventArgs e)
@@ -396,4 +508,17 @@ public partial class SplitDrawingForm : Form
         var pieceCount = _splitLines.Count == 0 ? 1 : BuildPreviewRegions().Count;
         lblStatus.Text = $"Part: {_drawingBounds.Width:F2} x {_drawingBounds.Length:F2} | {_splitLines.Count} split lines | {pieceCount} pieces";
     }
+
+    // --- SplitPreview control ---
+
+    private class SplitPreview : EntityView
+    {
+        public Action<Graphics> DrawOverlays { get; set; }
+
+        protected override void OnPaint(PaintEventArgs e)
+        {
+            base.OnPaint(e);
+            DrawOverlays?.Invoke(e.Graphics);
+        }
+    }
 }

OpenNest/Forms/SplitDrawingForm.resx

@@ -0,0 +1,126 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <!--
+    Microsoft ResX Schema
+
+    Version 2.0
+
+    The primary goals of this format is to allow a simple XML format
+    that is mostly human readable. The generation and parsing of the
+    various data types are done through the TypeConverter classes
+    associated with the data types.
+
+    Example:
+
+    ... ado.net/XML headers & schema ...
+    <resheader name="resmimetype">text/microsoft-resx</resheader>
+    <resheader name="version">2.0</resheader>
+    <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>
+    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>
+    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>
+    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>
+    <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">
+        <value>[base64 mime encoded serialized .NET Framework object]</value>
+    </data>
+    <data name="Icon1" type="System.Drawing.Icon, System.Drawing" mimetype="application/x-microsoft.net.object.bytearray.base64">
+        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
+        <comment>This is a comment</comment>
+    </data>
+
+    There are any number of "resheader" rows that contain simple
+    name/value pairs.
+
+    Each data row contains a name, and value. The row also contains a
+    type or mimetype. Type corresponds to a .NET class that support
+    text/value conversion through the TypeConverter architecture.
+    Classes that don't support this are serialized and stored with the
+    mimetype set.
+
+    The mimetype is used for serialized objects, and tells the
+    ResXResourceReader how to depersist the object. This is currently not
+    extensible. For a given mimetype the value must be set accordingly:
+
+    Note - application/x-microsoft.net.object.binary.base64 is the format
+    that the ResXResourceWriter will generate, however the reader can
+    read any of the formats listed below.
+
+    mimetype: application/x-microsoft.net.object.binary.base64
+    value   : The object must be serialized with
+            : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
+            : and then encoded with base64 encoding.
+
+    mimetype: application/x-microsoft.net.object.soap.base64
+    value   : The object must be serialized with
+            : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
+            : and then encoded with base64 encoding.
+
+    mimetype: application/x-microsoft.net.object.bytearray.base64
+    value   : The object must be serialized into a byte array
+            : using a System.ComponentModel.TypeConverter
+            : and then encoded with base64 encoding.
+    -->
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />
+    <xsd:element name="root" msdata:IsDataSet="true">
+      <xsd:complexType>
+        <xsd:choice maxOccurs="unbounded">
+          <xsd:element name="metadata">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" />
+              </xsd:sequence>
+              <xsd:attribute name="name" use="required" type="xsd:string" />
+              <xsd:attribute name="type" type="xsd:string" />
+              <xsd:attribute name="mimetype" type="xsd:string" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="assembly">
+            <xsd:complexType>
+              <xsd:attribute name="alias" type="xsd:string" />
+              <xsd:attribute name="name" type="xsd:string" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="data">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />
+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />
+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="resheader">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" />
+            </xsd:complexType>
+          </xsd:element>
+        </xsd:choice>
+      </xsd:complexType>
+    </xsd:element>
+  </xsd:schema>
+  <resheader name="resmimetype">
+    <value>text/microsoft-resx</value>
+  </resheader>
+  <resheader name="version">
+    <value>2.0</value>
+  </resheader>
+  <resheader name="reader">
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <resheader name="writer">
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <metadata name="toolStrip.TrayLocation" type="System.Drawing.Point, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a">
+    <value>17, 17</value>
+  </metadata>
+  <metadata name="statusStrip.TrayLocation" type="System.Drawing.Point, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a">
+    <value>116, 17</value>
+  </metadata>
+</root>

OpenNest/LayoutPart.cs

@@ -182,7 +182,7 @@ namespace OpenNest
 
             foreach (var shape in shapes)
             {
-                var offsetEntity = shape.OffsetEntity(spacing, OffsetSide.Left) as Shape;
+                var offsetEntity = shape.OffsetOutward(spacing);
 
                 if (offsetEntity == null)
                     continue;