feat(ui): add drawing selector, color scheme, and async loading to BestFitViewer

Add drawing dropdown to switch between drawings without reopening the
form. Change color scheme to light backgrounds with blue/red part fills
and auto-detect text color. Fix swapped bounding box width/length. Run
best-fit computation on a background thread so the UI stays responsive
during long calculations, with cancellation on drawing switch.

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

OpenNest/Controls/BestFitCell.cs

@@ -9,9 +9,16 @@ namespace OpenNest.Controls
     public class BestFitCell : PlateView
     {
         private string[] metadataLines;
+        private Color? partColor;
 
         public BestFitResult Result { get; set; }
 
+        public Color? PartColor
+        {
+            get => partColor;
+            set => partColor = value;
+        }
+
         public BestFitCell(ColorScheme colorScheme)
             : base(colorScheme)
         {
@@ -22,6 +29,8 @@ namespace OpenNest.Controls
             AllowZoom = false;
             AllowDrop = false;
             Cursor = Cursors.Hand;
+
+            Plate.PartAdded += (s, e) => ApplyPartColor();
         }
 
         public void SetMetadata(BestFitResult result, int rank)
@@ -59,13 +68,22 @@ namespace OpenNest.Controls
             PaintMetadata(e.Graphics);
         }
 
+        private void ApplyPartColor()
+        {
+            if (!partColor.HasValue)
+                return;
+
+            foreach (var lp in parts)
+                lp.Color = partColor.Value;
+        }
+
         private void PaintMetadata(Graphics g)
         {
             if (metadataLines == null)
                 return;
 
             var font = Font;
-            var brush = Brushes.White;
+            var textColor = IsDarkBackground() ? Brushes.White : Brushes.Black;
             var lineHeight = font.GetHeight(g) + 1;
             var y = 2f;
 
@@ -74,9 +92,16 @@ namespace OpenNest.Controls
                 if (line.Length == 0)
                     continue;
 
-                g.DrawString(line, font, brush, 2, y);
+                g.DrawString(line, font, textColor, 2, y);
                 y += lineHeight;
             }
         }
+
+        private bool IsDarkBackground()
+        {
+            var bg = ColorScheme.BackgroundColor;
+            var brightness = bg.R * 0.299 + bg.G * 0.587 + bg.B * 0.114;
+            return brightness < 128;
+        }
     }
 }

OpenNest/Controls/PlateView.cs

@@ -30,7 +30,7 @@ namespace OpenNest.Controls
         private Plate plate;
         private Action currentAction;
         private Action previousAction;
-        private List<LayoutPart> parts;
+        protected List<LayoutPart> parts;
         private List<LayoutPart> stationaryParts = new List<LayoutPart>();
         private List<LayoutPart> activeParts = new List<LayoutPart>();
         private Point middleMouseDownPoint;

OpenNest/Forms/BestFitViewerForm.Designer.cs

@@ -14,11 +14,15 @@ namespace OpenNest.Forms
         private void InitializeComponent()
         {
             this.gridPanel = new System.Windows.Forms.TableLayoutPanel();
+            this.toolbarPanel = new System.Windows.Forms.Panel();
+            this.lblDrawing = new System.Windows.Forms.Label();
+            this.cboDrawing = new System.Windows.Forms.ComboBox();
             this.navPanel = new System.Windows.Forms.Panel();
             this.btnPrev = new System.Windows.Forms.Button();
             this.btnNext = new System.Windows.Forms.Button();
             this.txtPage = new System.Windows.Forms.TextBox();
             this.lblPageCount = new System.Windows.Forms.Label();
+            this.toolbarPanel.SuspendLayout();
             this.navPanel.SuspendLayout();
             this.SuspendLayout();
             //
@@ -31,15 +35,42 @@ namespace OpenNest.Forms
             this.gridPanel.ColumnStyles.Add(new System.Windows.Forms.ColumnStyle(System.Windows.Forms.SizeType.Percent, 20F));
             this.gridPanel.ColumnStyles.Add(new System.Windows.Forms.ColumnStyle(System.Windows.Forms.SizeType.Percent, 20F));
             this.gridPanel.Dock = System.Windows.Forms.DockStyle.Fill;
-            this.gridPanel.Location = new System.Drawing.Point(0, 0);
+            this.gridPanel.Location = new System.Drawing.Point(0, 32);
             this.gridPanel.Name = "gridPanel";
             this.gridPanel.RowCount = 3;
             this.gridPanel.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 33.33F));
             this.gridPanel.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 33.34F));
             this.gridPanel.RowStyles.Add(new System.Windows.Forms.RowStyle(System.Windows.Forms.SizeType.Percent, 33.33F));
-            this.gridPanel.Size = new System.Drawing.Size(1200, 764);
+            this.gridPanel.Size = new System.Drawing.Size(1200, 732);
             this.gridPanel.TabIndex = 0;
             //
+            // toolbarPanel
+            //
+            this.toolbarPanel.Controls.Add(this.lblDrawing);
+            this.toolbarPanel.Controls.Add(this.cboDrawing);
+            this.toolbarPanel.Dock = System.Windows.Forms.DockStyle.Top;
+            this.toolbarPanel.Location = new System.Drawing.Point(0, 0);
+            this.toolbarPanel.Name = "toolbarPanel";
+            this.toolbarPanel.Size = new System.Drawing.Size(1200, 32);
+            this.toolbarPanel.TabIndex = 2;
+            //
+            // lblDrawing
+            //
+            this.lblDrawing.Location = new System.Drawing.Point(6, 0);
+            this.lblDrawing.Name = "lblDrawing";
+            this.lblDrawing.Size = new System.Drawing.Size(55, 32);
+            this.lblDrawing.TabIndex = 0;
+            this.lblDrawing.Text = "Drawing:";
+            this.lblDrawing.TextAlign = System.Drawing.ContentAlignment.MiddleLeft;
+            //
+            // cboDrawing
+            //
+            this.cboDrawing.DropDownStyle = System.Windows.Forms.ComboBoxStyle.DropDownList;
+            this.cboDrawing.Location = new System.Drawing.Point(64, 5);
+            this.cboDrawing.Name = "cboDrawing";
+            this.cboDrawing.Size = new System.Drawing.Size(250, 21);
+            this.cboDrawing.TabIndex = 1;
+            //
             // navPanel
             //
             this.navPanel.Controls.Add(this.btnPrev);
@@ -54,9 +85,7 @@ namespace OpenNest.Forms
             //
             // btnPrev
             //
-            this.btnPrev.Anchor = System.Windows.Forms.AnchorStyles.Top;
             this.btnPrev.FlatStyle = System.Windows.Forms.FlatStyle.Flat;
-            this.btnPrev.Location = new System.Drawing.Point(480, 4);
             this.btnPrev.Name = "btnPrev";
             this.btnPrev.Size = new System.Drawing.Size(80, 28);
             this.btnPrev.TabIndex = 0;
@@ -65,8 +94,6 @@ namespace OpenNest.Forms
             //
             // txtPage
             //
-            this.txtPage.Anchor = System.Windows.Forms.AnchorStyles.Top;
-            this.txtPage.Location = new System.Drawing.Point(564, 7);
             this.txtPage.Name = "txtPage";
             this.txtPage.Size = new System.Drawing.Size(40, 20);
             this.txtPage.TabIndex = 1;
@@ -76,8 +103,6 @@ namespace OpenNest.Forms
             //
             // lblPageCount
             //
-            this.lblPageCount.Anchor = System.Windows.Forms.AnchorStyles.Top;
-            this.lblPageCount.Location = new System.Drawing.Point(606, 4);
             this.lblPageCount.Name = "lblPageCount";
             this.lblPageCount.Size = new System.Drawing.Size(50, 28);
             this.lblPageCount.TabIndex = 2;
@@ -86,9 +111,7 @@ namespace OpenNest.Forms
             //
             // btnNext
             //
-            this.btnNext.Anchor = System.Windows.Forms.AnchorStyles.Top;
             this.btnNext.FlatStyle = System.Windows.Forms.FlatStyle.Flat;
-            this.btnNext.Location = new System.Drawing.Point(660, 4);
             this.btnNext.Name = "btnNext";
             this.btnNext.Size = new System.Drawing.Size(80, 28);
             this.btnNext.TabIndex = 3;
@@ -101,18 +124,23 @@ namespace OpenNest.Forms
             this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
             this.ClientSize = new System.Drawing.Size(1200, 800);
             this.Controls.Add(this.gridPanel);
+            this.Controls.Add(this.toolbarPanel);
             this.Controls.Add(this.navPanel);
             this.KeyPreview = true;
             this.Name = "BestFitViewerForm";
             this.StartPosition = System.Windows.Forms.FormStartPosition.CenterParent;
             this.Text = "Best-Fit Viewer";
             this.WindowState = System.Windows.Forms.FormWindowState.Maximized;
+            this.toolbarPanel.ResumeLayout(false);
             this.navPanel.ResumeLayout(false);
             this.navPanel.PerformLayout();
             this.ResumeLayout(false);
         }
 
         private System.Windows.Forms.TableLayoutPanel gridPanel;
+        private System.Windows.Forms.Panel toolbarPanel;
+        private System.Windows.Forms.Label lblDrawing;
+        private System.Windows.Forms.ComboBox cboDrawing;
         private System.Windows.Forms.Panel navPanel;
         private System.Windows.Forms.Button btnPrev;
         private System.Windows.Forms.Button btnNext;

OpenNest/Forms/BestFitViewerForm.cs

@@ -1,10 +1,14 @@
+using OpenNest.Collections;
 using OpenNest.Controls;
 using OpenNest.Engine.BestFit;
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Drawing;
+using System.Linq;
 using System.Runtime.InteropServices;
+using System.Threading;
+using System.Threading.Tasks;
 using System.Windows.Forms;
 
 namespace OpenNest.Forms
@@ -20,12 +24,15 @@ namespace OpenNest.Forms
         private const int Rows = 3;
         private const int ItemsPerPage = Columns * Rows;
 
-        private static readonly Color KeptColor = Color.FromArgb(0, 0, 100);
+        private static readonly Color KeptBackground = Color.FromArgb(240, 240, 240);
-        private static readonly Color DroppedColor = Color.FromArgb(100, 0, 0);
+        private static readonly Color DroppedBackground = Color.FromArgb(255, 235, 235);
+        private static readonly Color KeptPartColor = Color.FromArgb(50, 120, 190);
+        private static readonly Color DroppedPartColor = Color.FromArgb(180, 80, 80);
 
-        private readonly Drawing drawing;
+        private readonly List<Drawing> drawings;
         private readonly Plate plate;
 
+        private Drawing activeDrawing;
         private List<BestFitResult> results;
         private int totalResults;
         private int keptCount;
@@ -33,30 +40,37 @@ namespace OpenNest.Forms
         private double totalSeconds;
         private int currentPage;
         private int pageCount;
+        private CancellationTokenSource computeCts;
 
         public BestFitResult SelectedResult { get; private set; }
+        public Drawing SelectedDrawing => activeDrawing;
 
-        public BestFitViewerForm(Drawing drawing, Plate plate)
+        public BestFitViewerForm(DrawingCollection drawings, Plate plate)
         {
-            this.drawing = drawing;
+            this.drawings = drawings.ToList();
             this.plate = plate;
+            this.activeDrawing = this.drawings[0];
             DoubleBuffered = true;
             InitializeComponent();
+
+            foreach (var d in drawings)
+                cboDrawing.Items.Add(d.Name);
+            cboDrawing.SelectedIndex = 0;
+            cboDrawing.SelectedIndexChanged += cboDrawing_SelectedIndexChanged;
+
+            navPanel.SizeChanged += (s, ev) => CenterNavControls();
             Shown += BestFitViewerForm_Shown;
         }
 
-        private void BestFitViewerForm_Shown(object sender, System.EventArgs e)
+        private void BestFitViewerForm_Shown(object sender, EventArgs e)
         {
-            Cursor = Cursors.WaitCursor;
+            LoadResultsAsync();
-            try
+        }
-            {
+
-                ComputeResults();
+        protected override void OnFormClosed(FormClosedEventArgs e)
-                ShowPage(0);
+        {
-            }
+            computeCts?.Cancel();
-            finally
+            base.OnFormClosed(e);
-            {
-                Cursor = Cursors.Default;
-            }
         }
 
         protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
@@ -79,27 +93,97 @@ namespace OpenNest.Forms
             return base.ProcessCmdKey(ref msg, keyData);
         }
 
-        private void ComputeResults()
+        private void cboDrawing_SelectedIndexChanged(object sender, EventArgs e)
+        {
+            var index = cboDrawing.SelectedIndex;
+            if (index < 0 || index >= drawings.Count)
+                return;
+
+            activeDrawing = drawings[index];
+            LoadResultsAsync();
+        }
+
+        private async void LoadResultsAsync()
+        {
+            computeCts?.Cancel();
+            var cts = new CancellationTokenSource();
+            computeCts = cts;
+
+            SetLoading(true);
+
+            try
+            {
+                var drawing = activeDrawing;
+                var length = plate.Size.Length;
+                var width = plate.Size.Width;
+                var spacing = plate.PartSpacing;
+
+                var result = await Task.Run(() => ComputeResults(drawing, length, width, spacing), cts.Token);
+
+                if (cts.Token.IsCancellationRequested)
+                    return;
+
+                results = result.Results;
+                totalResults = result.TotalResults;
+                keptCount = result.KeptCount;
+                computeSeconds = result.ComputeSeconds;
+                totalSeconds = result.TotalSeconds;
+                pageCount = System.Math.Max(1, (int)System.Math.Ceiling(results.Count / (double)ItemsPerPage));
+
+                ShowPage(0);
+            }
+            catch (OperationCanceledException)
+            {
+            }
+            finally
+            {
+                if (cts == computeCts)
+                    SetLoading(false);
+            }
+        }
+
+        private void SetLoading(bool loading)
+        {
+            Cursor = loading ? Cursors.WaitCursor : Cursors.Default;
+            cboDrawing.Enabled = !loading;
+            btnPrev.Enabled = !loading;
+            btnNext.Enabled = !loading;
+            txtPage.Enabled = !loading;
+
+            if (loading)
+            {
+                Text = "Best-Fit Viewer — Computing...";
+                gridPanel.SuspendLayout();
+                gridPanel.Controls.Clear();
+                gridPanel.ResumeLayout(true);
+            }
+        }
+
+        private static ComputeResult ComputeResults(Drawing drawing, double length, double width, double spacing)
         {
             var sw = Stopwatch.StartNew();
 
-            var all = BestFitCache.GetOrCompute(
+            var all = BestFitCache.GetOrCompute(drawing, length, width, spacing);
-                drawing, plate.Size.Length, plate.Size.Width, plate.PartSpacing);
 
-            computeSeconds = sw.ElapsedMilliseconds / 1000.0;
+            var computeMs = sw.ElapsedMilliseconds;
-            totalResults = all.Count;
+            var total = all.Count;
-            keptCount = 0;
+            var kept = 0;
 
             foreach (var r in all)
             {
-                if (r.Keep) keptCount++;
+                if (r.Keep) kept++;
             }
 
-            results = all;
-            pageCount = System.Math.Max(1, (int)System.Math.Ceiling(results.Count / (double)ItemsPerPage));
-
             sw.Stop();
-            totalSeconds = sw.Elapsed.TotalSeconds;
+
+            return new ComputeResult
+            {
+                Results = all,
+                TotalResults = total,
+                KeptCount = kept,
+                ComputeSeconds = computeMs / 1000.0,
+                TotalSeconds = sw.Elapsed.TotalSeconds
+            };
         }
 
         private void ShowPage(int page)
@@ -122,7 +206,7 @@ namespace OpenNest.Forms
                 for (var i = 0; i < count; i++)
                 {
                     var result = results[start + i];
-                    var cell = CreateCell(result, drawing, start + i + 1);
+                    var cell = CreateCell(result, activeDrawing, start + i + 1);
                     gridPanel.Controls.Add(cell, i % Columns, i / Columns);
                 }
 
@@ -144,9 +228,28 @@ namespace OpenNest.Forms
                 start + 1, start + count, results.Count);
         }
 
-        private void btnPrev_Click(object sender, System.EventArgs e) => NavigatePage(-1);
+        private void btnPrev_Click(object sender, EventArgs e) => NavigatePage(-1);
 
-        private void btnNext_Click(object sender, System.EventArgs e) => NavigatePage(1);
+        private void btnNext_Click(object sender, EventArgs e) => NavigatePage(1);
+
+        private void CenterNavControls()
+        {
+            var gap = 6;
+            var groupWidth = btnPrev.Width + gap + txtPage.Width + gap + lblPageCount.Width + gap + btnNext.Width;
+            var x = (navPanel.Width - groupWidth) / 2;
+            var midY = navPanel.Height / 2;
+
+            btnPrev.Location = new Point(x, midY - btnPrev.Height / 2);
+            x += btnPrev.Width + gap;
+
+            txtPage.Location = new Point(x, midY - txtPage.Height / 2);
+            x += txtPage.Width + gap;
+
+            lblPageCount.Location = new Point(x, midY - lblPageCount.Height / 2);
+            x += lblPageCount.Width + gap;
+
+            btnNext.Location = new Point(x, midY - btnNext.Height / 2);
+        }
 
         private void NavigatePage(int delta)
         {
@@ -169,12 +272,14 @@ namespace OpenNest.Forms
 
         private BestFitCell CreateCell(BestFitResult result, Drawing drawing, int rank)
         {
-            var bgColor = result.Keep ? KeptColor : DroppedColor;
+            var kept = result.Keep;
+            var bgColor = kept ? KeptBackground : DroppedBackground;
+            var partColor = kept ? KeptPartColor : DroppedPartColor;
 
             var colorScheme = new ColorScheme
             {
                 BackgroundColor = bgColor,
-                LayoutOutlineColor = bgColor,
+                LayoutOutlineColor = Color.Gray,
                 LayoutFillColor = bgColor,
                 BoundingBoxColor = bgColor,
                 RapidColor = Color.DodgerBlue,
@@ -183,10 +288,11 @@ namespace OpenNest.Forms
             };
 
             var cell = new BestFitCell(colorScheme);
+            cell.PartColor = partColor;
             cell.Dock = DockStyle.Fill;
             cell.Plate.Size = new Geometry.Size(
-                result.BoundingWidth,
+                result.BoundingHeight,
-                result.BoundingHeight);
+                result.BoundingWidth);
 
             var parts = result.BuildParts(drawing);
 
@@ -204,5 +310,14 @@ namespace OpenNest.Forms
 
             return cell;
         }
+
+        private struct ComputeResult
+        {
+            public List<BestFitResult> Results;
+            public int TotalResults;
+            public int KeptCount;
+            public double ComputeSeconds;
+            public double TotalSeconds;
+        }
     }
 }

OpenNest/Forms/MainForm.cs

@@ -576,22 +576,20 @@ namespace OpenNest.Forms
                 return;
 
             var plate = activeForm.PlateView.Plate;
-            var drawing = activeForm.Nest.Drawings.Count > 0
+            var drawings = activeForm.Nest.Drawings;
-                ? activeForm.Nest.Drawings.First()
-                : null;
 
-            if (drawing == null)
+            if (drawings.Count == 0)
             {
                 MessageBox.Show("No drawings available.", "Best-Fit Viewer",
                     MessageBoxButtons.OK, MessageBoxIcon.Information);
                 return;
             }
 
-            using (var form = new BestFitViewerForm(drawing, plate))
+            using (var form = new BestFitViewerForm(drawings, plate))
             {
                 if (form.ShowDialog(this) == DialogResult.OK && form.SelectedResult != null)
                 {
-                    var parts = form.SelectedResult.BuildParts(drawing);
+                    var parts = form.SelectedResult.BuildParts(form.SelectedDrawing);
                     activeForm.PlateView.SetAction(typeof(ActionClone), parts);
                 }
             }