feat(ui): draw library previews in one shared style from the color scheme

The Shape Library, drawing library and drawing set preview each drew
parts their own way (hardcoded green fill, steel-blue fallback, black
outlines with gray etch). They now share a library style on ColorScheme
(background, fill, outline, etch and bend colors) that ignores drawing
colors, follows the active scheme (Dark gets a dark variant) and
round-trips through saved schemes, defaulting when absent. Nest part
colors are unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.WinForms.Tests/Controls/LibraryPreviewStyleTests.cs

@@ -0,0 +1,68 @@
+using System.Drawing;
+using OpenNest.CNC;
+using OpenNest.Controls;
+
+namespace OpenNest.WinForms.Tests.Controls;
+
+public class LibraryPreviewStyleTests
+{
+    private const int ViewSize = 200;
+
+    [Fact]
+    public void LibraryColorsRoundTripAndOlderSchemesKeepTheDefaults()
+    {
+        var scheme = ColorSchemeRegistry.Get("Dark");
+        var restored = ColorSchemeSerializer.Deserialize(ColorSchemeSerializer.Serialize(scheme));
+
+        Assert.Equal(scheme.LibraryBackgroundColor.ToArgb(), restored.LibraryBackgroundColor.ToArgb());
+        Assert.Equal(scheme.LibraryFillColor.ToArgb(), restored.LibraryFillColor.ToArgb());
+        Assert.Equal(scheme.LibraryOutlineColor.ToArgb(), restored.LibraryOutlineColor.ToArgb());
+        Assert.Equal(scheme.LibraryEtchColor.ToArgb(), restored.LibraryEtchColor.ToArgb());
+        Assert.Equal(scheme.LibraryBendColor.ToArgb(), restored.LibraryBendColor.ToArgb());
+
+        var legacy = ColorSchemeSerializer.Deserialize("{\"name\":\"Old\",\"backgroundColor\":\"#101010\"}");
+        var defaults = new ColorScheme();
+        Assert.Equal(defaults.LibraryBackgroundColor.ToArgb(), legacy.LibraryBackgroundColor.ToArgb());
+        Assert.Equal(defaults.LibraryFillColor.ToArgb(), legacy.LibraryFillColor.ToArgb());
+        Assert.Equal(defaults.LibraryBendColor.ToArgb(), legacy.LibraryBendColor.ToArgb());
+    }
+
+    [Fact]
+    public void ShapePreviewFillsWithTheLibraryStyleNotTheDrawingColor() => ArchUnitsTests.RunSta(() =>
+    {
+        using var preview = new ShapePreviewControl { Size = new Size(ViewSize, ViewSize) };
+        preview.ShowDrawing(RedSquare());
+
+        AssertLibraryStyle(preview);
+    });
+
+    [Fact]
+    public void DrawingSetPreviewFillsWithTheLibraryStyleNotTheDrawingColor() => ArchUnitsTests.RunSta(() =>
+    {
+        using var preview = new DrawingSetPreviewControl { Size = new Size(ViewSize, ViewSize) };
+        preview.ShowDrawings(new[] { (RedSquare(), "") });
+
+        AssertLibraryStyle(preview);
+    });
+
+    private static void AssertLibraryStyle(PlateView preview)
+    {
+        using var bitmap = new Bitmap(ViewSize, ViewSize);
+        preview.DrawToBitmap(bitmap, new Rectangle(0, 0, ViewSize, ViewSize));
+        var scheme = ColorScheme.Default;
+
+        Assert.Equal(scheme.LibraryBackgroundColor.ToArgb(), preview.BackColor.ToArgb());
+        Assert.Equal(scheme.LibraryFillColor.ToArgb(), bitmap.GetPixel(ViewSize / 2, ViewSize / 2 + 10).ToArgb());
+    }
+
+    private static Drawing RedSquare()
+    {
+        var program = new Program();
+        program.Codes.Add(new RapidMove(0, 0));
+        program.Codes.Add(new LinearMove(10, 0));
+        program.Codes.Add(new LinearMove(10, 10));
+        program.Codes.Add(new LinearMove(0, 10));
+        program.Codes.Add(new LinearMove(0, 0));
+        return new Drawing("square", program) { Color = Color.Red };
+    }
+}

OpenNest/ColorScheme.cs

@@ -29,6 +29,18 @@ namespace OpenNest
 
         public Color EtchColor { get; set; } = Color.Lime;
 
+        // Library previews (Shape Library, drawing library, drawing set preview) show drawings
+        // that are not in the nest yet, so they share one style instead of nest part colors.
+        public Color LibraryBackgroundColor { get; set; } = Color.White;
+
+        public Color LibraryFillColor { get; set; } = Color.FromArgb(214, 219, 226);
+
+        public Color LibraryOutlineColor { get; set; } = Color.FromArgb(64, 70, 80);
+
+        public Color LibraryEtchColor { get; set; } = Color.FromArgb(0, 150, 60);
+
+        public Color LibraryBendColor { get; set; } = Color.FromArgb(40, 100, 210);
+
         public Color GetPartOutlineColor(Color fill) =>
             PartOutlineColor.IsEmpty ? System.Windows.Forms.ControlPaint.Dark(fill) : PartOutlineColor;
 

OpenNest/ColorSchemeRegistry.cs

@@ -72,6 +72,11 @@ namespace OpenNest
             d.PartOutlineColor = scheme.PartOutlineColor;
             d.SelectedPartColor = scheme.SelectedPartColor;
             d.EtchColor = scheme.EtchColor;
+            d.LibraryBackgroundColor = scheme.LibraryBackgroundColor;
+            d.LibraryFillColor = scheme.LibraryFillColor;
+            d.LibraryOutlineColor = scheme.LibraryOutlineColor;
+            d.LibraryEtchColor = scheme.LibraryEtchColor;
+            d.LibraryBendColor = scheme.LibraryBendColor;
 
             Drawing.PartColors = scheme.PartColors;
             Drawing.UseGoldenAngleColors = scheme.UseGoldenAngleColors;
@@ -333,6 +338,11 @@ namespace OpenNest
                 OriginColor = Color.FromArgb(120, 120, 130),
                 EdgeSpacingColor = Color.FromArgb(90, 90, 100),
                 PreviewPartColor = Color.FromArgb(255, 170, 60),
+                LibraryBackgroundColor = Color.FromArgb(30, 30, 34),
+                LibraryFillColor = Color.FromArgb(70, 76, 86),
+                LibraryOutlineColor = Color.FromArgb(205, 210, 220),
+                LibraryEtchColor = Color.FromArgb(120, 230, 120),
+                LibraryBendColor = Color.FromArgb(100, 180, 255),
                 PartColors = new[]
                 {
                     Color.FromArgb(255, 85, 85), // Neon Red

OpenNest/ColorSchemeSerializer.cs

@@ -29,6 +29,11 @@ namespace OpenNest
                 PartOutlineColor = scheme.PartOutlineColor.IsEmpty ? null : ToHex(scheme.PartOutlineColor),
                 SelectedPartColor = scheme.SelectedPartColor.IsEmpty ? null : ToHex(scheme.SelectedPartColor),
                 EtchColor = ToHex(scheme.EtchColor),
+                LibraryBackgroundColor = ToHex(scheme.LibraryBackgroundColor),
+                LibraryFillColor = ToHex(scheme.LibraryFillColor),
+                LibraryOutlineColor = ToHex(scheme.LibraryOutlineColor),
+                LibraryEtchColor = ToHex(scheme.LibraryEtchColor),
+                LibraryBendColor = ToHex(scheme.LibraryBendColor),
                 PartColors = scheme.PartColors.Select(ToHex).ToArray(),
                 UseGoldenAngleColors = scheme.UseGoldenAngleColors,
             };
@@ -41,7 +46,7 @@ namespace OpenNest
                 JsonSerializer.Deserialize<ColorSchemeDto>(json, JsonOptions)
                 ?? throw new JsonException("ColorScheme JSON was null");
 
-            return new ColorScheme
+            var scheme = new ColorScheme
             {
                 Name = dto.Name ?? "Unnamed",
                 BackgroundColor = FromHex(dto.BackgroundColor),
@@ -58,8 +63,19 @@ namespace OpenNest
                 PartColors = (dto.PartColors ?? new string[0]).Select(FromHex).ToArray(),
                 UseGoldenAngleColors = dto.UseGoldenAngleColors,
             };
+
+            // Schemes saved before the library style keep its defaults.
+            scheme.LibraryBackgroundColor = FromHexOr(dto.LibraryBackgroundColor, scheme.LibraryBackgroundColor);
+            scheme.LibraryFillColor = FromHexOr(dto.LibraryFillColor, scheme.LibraryFillColor);
+            scheme.LibraryOutlineColor = FromHexOr(dto.LibraryOutlineColor, scheme.LibraryOutlineColor);
+            scheme.LibraryEtchColor = FromHexOr(dto.LibraryEtchColor, scheme.LibraryEtchColor);
+            scheme.LibraryBendColor = FromHexOr(dto.LibraryBendColor, scheme.LibraryBendColor);
+            return scheme;
         }
 
+        private static Color FromHexOr(string hex, Color fallback) =>
+            string.IsNullOrWhiteSpace(hex) ? fallback : FromHex(hex);
+
         private static string ToHex(Color c) =>
             "#" + c.R.ToString("X2") + c.G.ToString("X2") + c.B.ToString("X2");
 
@@ -102,6 +118,11 @@ namespace OpenNest
             public string PartOutlineColor { get; set; }
             public string SelectedPartColor { get; set; }
             public string EtchColor { get; set; }
+            public string LibraryBackgroundColor { get; set; }
+            public string LibraryFillColor { get; set; }
+            public string LibraryOutlineColor { get; set; }
+            public string LibraryEtchColor { get; set; }
+            public string LibraryBendColor { get; set; }
             public string[] PartColors { get; set; }
             public bool UseGoldenAngleColors { get; set; }
         }

OpenNest/Controls/DrawingLibraryView.Designer.cs

@@ -514,7 +514,6 @@ namespace OpenNest.Controls
             previewBox.AllowPan = false;
             previewBox.AllowSelect = false;
             previewBox.AllowZoom = false;
-            previewBox.BackColor = System.Drawing.Color.White;
             previewBox.Cursor = System.Windows.Forms.Cursors.Default;
             previewBox.Dock = System.Windows.Forms.DockStyle.Fill;
             previewBox.Name = "previewBox";

OpenNest/Controls/DrawingSetPreviewControl.cs

@@ -8,7 +8,7 @@ using OpenNest.Geometry;
 namespace OpenNest.Controls
 {
     /// <summary>
-    /// Shows every drawing of a set side by side at one scale, outlined without fill, packed by
+    /// Shows every drawing of a set side by side at one scale in the library style, packed by
     /// <see cref="DrawingSetPreviewLayout"/> with a label under each and the info lines above.
     /// The layout is repacked to fit whenever the control is resized; the wheel zooms, the
     /// middle button pans and a middle double-click fits the set again.
@@ -29,7 +29,7 @@ namespace OpenNest.Controls
             AllowSelect = false;
             AllowZoom = true;
             AllowDrop = false;
-            BackColor = Color.White;
+            BackColor = ColorScheme.Default.LibraryBackgroundColor;
             // A large set in millimeters fits at well under the default floor of 0.3 px per unit.
             ViewScaleMin = 1e-5f;
         }
@@ -138,28 +138,13 @@ namespace OpenNest.Controls
             e.Graphics.SmoothingMode = SmoothingMode.HighQuality;
 
             e.Graphics.TranslateTransform(origin.X, origin.Y);
-            PaintOutlines(e.Graphics);
+            Renderer.DrawLibraryParts(e.Graphics, ColorScheme.Default);
             PaintLabels(e.Graphics);
             e.Graphics.ResetTransform();
 
             PaintInfo(e.Graphics);
         }
 
-        // Outlines only: cuts in black, etch marks dashed in gray.
-        private void PaintOutlines(Graphics g)
-        {
-            using var etchPen = new Pen(Color.Gray) { DashStyle = DashStyle.Dash };
-            foreach (var part in LayoutParts)
-            {
-                if (part.IsDirty)
-                    part.Update(this);
-                if (part.EtchPath?.PointCount > 0)
-                    g.DrawPath(etchPen, part.EtchPath);
-                if (part.Path?.PointCount > 0)
-                    g.DrawPath(Pens.Black, part.Path);
-            }
-        }
-
         private void PaintLabels(Graphics g)
         {
             if (layout == null)
@@ -172,13 +157,14 @@ namespace OpenNest.Controls
                 Trimming = StringTrimming.EllipsisCharacter,
                 FormatFlags = StringFormatFlags.NoWrap,
             };
+            using var text = new SolidBrush(ColorScheme.Default.LibraryOutlineColor);
 
             foreach (var placement in layout.Placements)
             {
                 var corner = PointWorldToGraph(placement.CellX, placement.LabelTop);
                 var rect = new RectangleF(corner.X, corner.Y + 1,
                     LengthWorldToGui(placement.CellWidth), System.Math.Max(LengthWorldToGui(layout.LabelHeight), Font.Height));
-                g.DrawString(items[placement.Index].Label, Font, Brushes.Black, rect, format);
+                g.DrawString(items[placement.Index].Label, Font, text, rect, format);
             }
         }
 
@@ -191,12 +177,13 @@ namespace OpenNest.Controls
                 Trimming = StringTrimming.EllipsisCharacter,
                 FormatFlags = StringFormatFlags.NoWrap,
             };
+            using var text = new SolidBrush(ColorScheme.Default.LibraryOutlineColor);
 
             foreach (var line in infoLines)
             {
                 if (string.IsNullOrEmpty(line))
                     continue;
-                g.DrawString(line, Font, Brushes.Black, new RectangleF(4, y, System.Math.Max(Width - 8, 1), lineHeight), format);
+                g.DrawString(line, Font, text, new RectangleF(4, y, System.Math.Max(Width - 8, 1), lineHeight), format);
                 y += lineHeight;
             }
         }

OpenNest/Controls/PlateRenderer.cs

@@ -109,6 +109,22 @@ namespace OpenNest.Controls
             );
         }
 
+        /// <summary>
+        /// Draws every part in <paramref name="scheme"/>'s library style with its bend lines,
+        /// without ids, selection or validation states.
+        /// </summary>
+        public void DrawLibraryParts(Graphics g, ColorScheme scheme)
+        {
+            using var bendPen = new Pen(scheme.LibraryBendColor, 1.5f) { DashStyle = DashStyle.Dash };
+            foreach (var part in view.DisplayLayoutParts)
+            {
+                if (part.IsDirty)
+                    part.UpdateView(view);
+                part.DrawLibrary(g, scheme);
+                DrawBendLines(g, part.BasePart, bendPen);
+            }
+        }
+
         public void DrawParts(Graphics g)
         {
             var viewBounds = view.GetViewBounds();
@@ -439,6 +455,13 @@ namespace OpenNest.Controls
             {
                 DashStyle = System.Drawing.Drawing2D.DashStyle.Dash,
             };
+            DrawBendLines(g, part, bendPen);
+        }
+
+        private void DrawBendLines(Graphics g, Part part, Pen bendPen)
+        {
+            if (part.BaseDrawing.Bends == null)
+                return;
 
             foreach (var bend in part.BaseDrawing.Bends)
             {

OpenNest/Controls/ShapePreviewControl.cs

@@ -16,7 +16,7 @@ namespace OpenNest.Controls
             AllowSelect = false;
             AllowZoom = false;
             AllowDrop = false;
-            BackColor = Color.White;
+            BackColor = ColorScheme.Default.LibraryBackgroundColor;
         }
 
         public void SetInfo(params string[] lines)
@@ -55,7 +55,7 @@ namespace OpenNest.Controls
 
             e.Graphics.TranslateTransform(origin.X, origin.Y);
             Renderer.DrawPlate(e.Graphics);
-            Renderer.DrawParts(e.Graphics);
+            Renderer.DrawLibraryParts(e.Graphics, ColorScheme.Default);
             e.Graphics.ResetTransform();
 
             PaintInfo(e.Graphics);
@@ -68,12 +68,13 @@ namespace OpenNest.Controls
 
             var lineHeight = Font.GetHeight(g) + 1;
             var y = 4f;
+            using var text = new SolidBrush(ColorScheme.Default.LibraryOutlineColor);
 
             foreach (var line in infoLines)
             {
                 if (string.IsNullOrEmpty(line))
                     continue;
-                g.DrawString(line, Font, Brushes.Black, 4, y);
+                g.DrawString(line, Font, text, 4, y);
                 y += lineHeight;
             }
         }

OpenNest/Forms/ShapeLibraryForm.Designer.cs

@@ -202,7 +202,6 @@ namespace OpenNest.Forms
             previewBox.AllowPan = false;
             previewBox.AllowSelect = false;
             previewBox.AllowZoom = false;
-            previewBox.BackColor = System.Drawing.Color.White;
             colorScheme1.BackgroundColor = System.Drawing.Color.DarkGray;
             colorScheme1.BoundingBoxColor = System.Drawing.Color.FromArgb(128, 128, 255);
             colorScheme1.EdgeSpacingColor = System.Drawing.Color.FromArgb(180, 180, 180);

OpenNest/Forms/ShapeLibraryForm.cs

@@ -27,9 +27,6 @@ namespace OpenNest.Forms
         private const int TileColumns = 3;
         private const int LVM_SETICONSPACING = 0x1000 + 53;
 
-        // The fill the preview gives a drawing without a color, so tiles match it.
-        private static readonly Color ThumbnailFill = Color.FromArgb(130, 204, 130);
-
         [DllImport("user32.dll")]
         private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam);
 
@@ -125,6 +122,8 @@ namespace OpenNest.Forms
                 ImageSize = new Size(ThumbnailSize, ThumbnailSize),
             };
             shapeListView.LargeImageList = images;
+            shapeListView.BackColor = ColorScheme.Default.LibraryBackgroundColor;
+            shapeListView.ForeColor = ColorScheme.Default.LibraryOutlineColor;
             shapeListView.HandleCreated += (_, _) => ApplyTileSpacing();
             Disposed += (_, _) => images.Dispose();
 
@@ -161,9 +160,10 @@ namespace OpenNest.Forms
                 // GetImage draws without antialiasing; render at twice the size and
                 // downsample so curved edges stay smooth at thumbnail scale.
                 var renderSize = new Size(ThumbnailSize * 2, ThumbnailSize * 2);
-                using var brush = new SolidBrush(ThumbnailFill);
-                using var pen = new Pen(ColorScheme.Default.GetPartOutlineColor(ThumbnailFill), 2f);
-                using var large = program.GetImage(renderSize, pen, brush);
+                var scheme = ColorScheme.Default;
+                using var brush = new SolidBrush(scheme.LibraryFillColor);
+                using var pen = new Pen(scheme.LibraryOutlineColor, 2f);
+                using var large = program.GetImage(renderSize, pen, brush, scheme.LibraryEtchColor);
                 using var graphics = Graphics.FromImage(thumbnail);
                 graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
                 graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;

OpenNest/GraphicsHelper.cs

@@ -108,7 +108,8 @@ namespace OpenNest
             this Program pgm,
             System.Drawing.Size size,
             Pen pen,
-            Brush brush
+            Brush brush,
+            Color? etchColor = null
         )
         {
             var img = new Bitmap(size.Width, size.Height);
@@ -152,7 +153,7 @@ namespace OpenNest
             if (pen == null)
                 pen = Pens.Black;
 
-            using var etchPen = new Pen(ColorScheme.Default.EtchColor, 1.5f);
+            using var etchPen = new Pen(etchColor ?? ColorScheme.Default.EtchColor, 1.5f);
             graphics.DrawPath(etchPen, etchPath);
             // A coincident cut must remain visible over an etch.
             graphics.DrawPath(pen, path);

OpenNest/LayoutPart.cs

@@ -143,6 +143,23 @@ namespace OpenNest
                 g.DrawPath(muted ? Pens.Gray : LeadInPen, LeadInPath);
         }
 
+        /// <summary>
+        /// Draws the part in the scheme's library style, ignoring its drawing color: library
+        /// previews show drawings that are not in the nest yet.
+        /// </summary>
+        internal void DrawLibrary(Graphics g, ColorScheme scheme)
+        {
+            using var fill = new SolidBrush(scheme.LibraryFillColor);
+            using var outline = new Pen(scheme.LibraryOutlineColor);
+            using var etch = new Pen(scheme.LibraryEtchColor, 1.5f);
+            g.FillPath(fill, MaterialPath);
+            DrawDisplay(g, false);
+            if (EtchPath?.PointCount > 0)
+                g.DrawPath(etch, EtchPath);
+            // Keep real cuts visible even where an etch overlaps them.
+            g.DrawPath(outline, Path);
+        }
+
         public void Draw(Graphics g, string id) => Draw(g, id, false);
 
         internal void Draw(Graphics g, string id, bool muted)