feat: add BestFitCell control with screen-space text overlay

Extract a BestFitCell subclass from PlateView for the Best-Fit Viewer
grid cells. Text metadata is now painted in screen coordinates (after
resetting the graphics transform) so it stays fixed regardless of zoom.
Parts auto-zoom to fit on every resize.

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

OpenNest/Controls/BestFitCell.cs

@@ -0,0 +1,82 @@
+using System.Drawing;
+using System.Drawing.Drawing2D;
+using System.Windows.Forms;
+using OpenNest.Engine.BestFit;
+using OpenNest.Math;
+
+namespace OpenNest.Controls
+{
+    public class BestFitCell : PlateView
+    {
+        private string[] metadataLines;
+
+        public BestFitResult Result { get; set; }
+
+        public BestFitCell(ColorScheme colorScheme)
+            : base(colorScheme)
+        {
+            DrawOrigin = false;
+            DrawBounds = false;
+            AllowPan = false;
+            AllowSelect = false;
+            AllowZoom = false;
+            AllowDrop = false;
+            Cursor = Cursors.Hand;
+        }
+
+        public void SetMetadata(BestFitResult result, int rank)
+        {
+            Result = result;
+
+            metadataLines = new[]
+            {
+                string.Format("#{0}  {1:F1}x{2:F1}  Area={3:F1}",
+                    rank, result.BoundingWidth, result.BoundingHeight, result.RotatedArea),
+                string.Format("Util={0:P1}  Rot={1:F1}\u00b0",
+                    result.Utilization,
+                    Angle.ToDegrees(result.OptimalRotation)),
+                result.Keep ? "" : result.Reason
+            };
+        }
+
+        protected override void OnResize(System.EventArgs e)
+        {
+            base.OnResize(e);
+
+            if (Plate.Parts.Count > 0)
+                ZoomToFit(false);
+        }
+
+        protected override void OnPaint(PaintEventArgs e)
+        {
+            e.Graphics.SmoothingMode = SmoothingMode.HighSpeed;
+
+            e.Graphics.TranslateTransform(origin.X, origin.Y);
+            DrawPlate(e.Graphics);
+            DrawParts(e.Graphics);
+            e.Graphics.ResetTransform();
+
+            PaintMetadata(e.Graphics);
+        }
+
+        private void PaintMetadata(Graphics g)
+        {
+            if (metadataLines == null)
+                return;
+
+            var font = Font;
+            var brush = Brushes.White;
+            var lineHeight = font.GetHeight(g) + 1;
+            var y = 2f;
+
+            foreach (var line in metadataLines)
+            {
+                if (line.Length == 0)
+                    continue;
+
+                g.DrawString(line, font, brush, 2, y);
+                y += lineHeight;
+            }
+        }
+    }
+}

OpenNest/Controls/PlateView.cs

@@ -370,7 +370,7 @@ namespace OpenNest.Controls
             Invalidate();
         }
 
-        private void DrawPlate(Graphics g)
+        protected void DrawPlate(Graphics g)
         {
             var plateRect = new RectangleF
             {
@@ -441,7 +441,7 @@ namespace OpenNest.Controls
                 plateRect.Height);
         }
 
-        private void DrawParts(Graphics g)
+        protected void DrawParts(Graphics g)
         {
             var viewBounds = new RectangleF(-origin.X, -origin.Y, Width, Height);
 
@@ -856,10 +856,13 @@ namespace OpenNest.Controls
             var stationaryBoxes = new List<Box>(stationaryParts.Count);
 
             var opposite = Helper.OppositeDirection(direction);
+            var halfSpacing = Plate.PartSpacing / 2;
 
             foreach (var part in stationaryParts)
             {
-                stationaryLines.Add(Helper.GetPartLines(part.BasePart, opposite));
+                stationaryLines.Add(halfSpacing > 0
+                    ? Helper.GetOffsetPartLines(part.BasePart, halfSpacing, opposite)
+                    : Helper.GetPartLines(part.BasePart, opposite));
                 stationaryBoxes.Add(part.BoundingBox);
             }
 
@@ -868,9 +871,9 @@ namespace OpenNest.Controls
 
             foreach (var selected in SelectedParts)
             {
-                // Get offset lines for the moving part.
-                var movingLines = Plate.PartSpacing > 0
-                    ? Helper.GetOffsetPartLines(selected.BasePart, Plate.PartSpacing, direction)
+                // Get offset lines for the moving part (half-spacing, symmetric with stationary).
+                var movingLines = halfSpacing > 0
+                    ? Helper.GetOffsetPartLines(selected.BasePart, halfSpacing, direction)
                     : Helper.GetPartLines(selected.BasePart, direction);
 
                 var movingBox = selected.BoundingBox;

OpenNest/Forms/BestFitViewerForm.cs

@@ -1,11 +1,8 @@
-using System.Collections.Generic;
 using System.Diagnostics;
 using System.Drawing;
 using System.Windows.Forms;
 using OpenNest.Controls;
 using OpenNest.Engine.BestFit;
-using OpenNest.Geometry;
-using OpenNest.Math;
 
 namespace OpenNest.Forms
 {
@@ -85,8 +82,8 @@ namespace OpenNest.Forms
                 for (var i = 0; i < count; i++)
                 {
                     var result = results[i];
-                    var view = CreateCellView(result, drawing, i + 1);
-                    gridPanel.Controls.Add(view, i % Columns, i / Columns);
+                    var cell = CreateCell(result, drawing, i + 1);
+                    gridPanel.Controls.Add(cell, i % Columns, i / Columns);
                 }
             }
             finally
@@ -99,7 +96,7 @@ namespace OpenNest.Forms
                 total, kept, findMs / 1000.0, sw.Elapsed.TotalSeconds, count);
         }
 
-        private PlateView CreateCellView(BestFitResult result, Drawing drawing, int rank)
+        private BestFitCell CreateCell(BestFitResult result, Drawing drawing, int rank)
         {
             var bgColor = result.Keep ? KeptColor : DroppedColor;
 
@@ -114,70 +111,27 @@ namespace OpenNest.Forms
                 EdgeSpacingColor = bgColor
             };
 
-            var view = new PlateView(colorScheme);
-            view.DrawOrigin = false;
-            view.DrawBounds = false;
-            view.AllowPan = false;
-            view.AllowSelect = false;
-            view.AllowZoom = false;
-            view.AllowDrop = false;
-            view.Dock = DockStyle.Fill;
-            view.Plate.Size = new Geometry.Size(
+            var cell = new BestFitCell(colorScheme);
+            cell.Dock = DockStyle.Fill;
+            cell.Plate.Size = new Geometry.Size(
                 result.BoundingWidth,
                 result.BoundingHeight);
 
             var parts = result.BuildParts(drawing);
 
             foreach (var part in parts)
-                view.Plate.Parts.Add(part);
+                cell.Plate.Parts.Add(part);
 
-            view.Paint += (sender, e) =>
-            {
-                PaintMetadata(e.Graphics, view, result, rank);
-            };
+            cell.SetMetadata(result, rank);
 
-            view.Resize += (sender, e) =>
-            {
-                view.ZoomToFit(false);
-            };
-
-            view.DoubleClick += (sender, e) =>
+            cell.DoubleClick += (sender, e) =>
             {
                 SelectedResult = result;
                 DialogResult = DialogResult.OK;
                 Close();
             };
 
-            view.Cursor = Cursors.Hand;
-
-            return view;
-        }
-
-        private void PaintMetadata(Graphics g, PlateView view, BestFitResult result, int rank)
-        {
-            var font = view.Font;
-            var brush = Brushes.White;
-            var lineHeight = font.GetHeight(g) + 1;
-
-            var lines = new[]
-            {
-                string.Format("#{0}  {1:F1}x{2:F1}  Area={3:F1}",
-                    rank, result.BoundingWidth, result.BoundingHeight, result.RotatedArea),
-                string.Format("Util={0:P1}  Rot={1:F1}\u00b0",
-                    result.Utilization,
-                    Angle.ToDegrees(result.OptimalRotation)),
-                result.Keep ? "" : result.Reason
-            };
-
-            var y = 2f;
-
-            foreach (var line in lines)
-            {
-                if (line.Length == 0)
-                    continue;
-                g.DrawString(line, font, brush, 2, y);
-                y += lineHeight;
-            }
+            return cell;
         }
     }
 }