feat(plateview): annotate overlap centroids

OpenNest.Core/Diagnostics/OverlapHoverPages.cs

@@ -0,0 +1,120 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+
+namespace OpenNest.Diagnostics;
+
+/// <summary>
+/// Viewport-sized pages of cached overlap details, including continuation pages for a
+/// single long pair. The caller supplies its actual single-line font measurement.
+/// No names or numeric details are elided, and no geometry is queried here.
+/// </summary>
+public sealed class OverlapHoverPages
+{
+    private readonly IReadOnlyList<string>[] pages;
+    private readonly IReadOnlyList<string>[] navigation;
+
+    private OverlapHoverPages(IReadOnlyList<string>[] pages, IReadOnlyList<string>[] navigation,
+        bool needsLargerViewport = false)
+    {
+        this.pages = pages;
+        this.navigation = navigation;
+        NeedsLargerViewport = needsLargerViewport;
+    }
+
+    public IReadOnlyList<string> Lines => PageCount == 0 ? Array.Empty<string>() : pages[PageIndex];
+    public IReadOnlyList<string> NavigationLines => PageCount == 0 ? Array.Empty<string>() : navigation[PageIndex];
+    public int PageIndex { get; private set; }
+    public int PageCount => pages.Length;
+    public bool NeedsLargerViewport { get; }
+
+    public void MovePage(int delta) => PageIndex = (int)System.Math.Clamp((long)PageIndex + delta, 0,
+        System.Math.Max(0, PageCount - 1));
+
+    public static OverlapHoverPages Create(string text, int pairCount, int maxRows,
+        double maxWidth, Func<string, double> measure)
+    {
+        var tooSmall = new OverlapHoverPages([], [], true);
+        if (maxRows < 1 || !double.IsFinite(maxWidth) || maxWidth <= 0)
+            return tooSmall;
+        var lines = Wrap(text, maxWidth, measure);
+        if (lines == null)
+            return tooSmall;
+        if (lines.Count <= maxRows)
+            return new OverlapHoverPages([lines.AsReadOnly()], [Array.Empty<string>()]);
+
+        // Reserve the real, wrapped hint as well as content. Increasing the reserved
+        // rows can increase the page count/digit count, so converge before slicing.
+        for (var hintRows = 2; hintRows < maxRows;)
+        {
+            var contentRows = maxRows - hintRows;
+            var count = (lines.Count - 1) / contentRows + 1;
+            var hints = new IReadOnlyList<string>[count];
+            var requiredHintRows = hintRows;
+            for (var page = 0; page < count; page++)
+            {
+                var hint = Wrap($"Page {page + 1}/{count} · {pairCount} pairs\nPgUp/PgDn", maxWidth, measure);
+                if (hint == null)
+                    return tooSmall;
+                hints[page] = hint.AsReadOnly();
+                requiredHintRows = System.Math.Max(requiredHintRows, hint.Count);
+            }
+            if (requiredHintRows > hintRows)
+            {
+                hintRows = requiredHintRows;
+                continue;
+            }
+            var pages = Enumerable.Range(0, count)
+                .Select(page => (IReadOnlyList<string>)Array.AsReadOnly(lines.Skip(page * contentRows).Take(contentRows).ToArray()))
+                .ToArray();
+            return new OverlapHoverPages(pages, hints);
+        }
+        // There must be room for at least one complete content line AND navigation.
+        return tooSmall;
+    }
+
+    private static List<string> Wrap(string text, double width, Func<string, double> measure)
+    {
+        var lines = new List<string>();
+        foreach (var paragraph in text.Replace("\r\n", "\n").Split('\n'))
+        {
+            if (paragraph.Length == 0)
+            {
+                lines.Add("");
+                continue;
+            }
+            var starts = StringInfo.ParseCombiningCharacters(paragraph).Append(paragraph.Length).ToArray();
+            for (var first = 0; first < starts.Length - 1;)
+            {
+                var low = first;
+                var high = starts.Length - 1;
+                while (low < high)
+                {
+                    var end = low + (high - low + 1) / 2;
+                    if (measure(paragraph[starts[first]..starts[end]]) <= width)
+                        low = end;
+                    else
+                        high = end - 1;
+                }
+                if (low == first)
+                    return null; // Even one grapheme cannot fit; do not silently clip it.
+                var last = low;
+                if (last < starts.Length - 1)
+                {
+                    for (var end = last; end > first; end--)
+                    {
+                        if (char.IsWhiteSpace(paragraph[starts[end - 1]]))
+                        {
+                            last = end;
+                            break;
+                        }
+                    }
+                }
+                lines.Add(paragraph[starts[first]..starts[last]]);
+                first = last;
+            }
+        }
+        return lines;
+    }
+}

OpenNest.Core/Diagnostics/OverlapPairPresentation.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using OpenNest.Geometry;
+
+namespace OpenNest.Diagnostics;
+
+/// <summary>Read-only pair presentation; no geometry preparation or collision queries.</summary>
+public static class OverlapPairPresentation
+{
+    public static string Label(PlateOverlapPair pair) => $"{pair.PartAId + 1}/{pair.PartBId + 1}";
+
+    public static string Details(PlateOverlapPair pair, Units capturedUnits, IFormatProvider provider = null)
+    {
+        var units = UnitsHelper.GetShortString(capturedUnits);
+        return $"Pair {Label(pair)}: {pair.PartAName} / {pair.PartBName}\n"
+            + $"Shared area ≈ {Number(pair.Area, provider)} {units}²\n"
+            + $"Centroid: ({Number(pair.Centroid.X, provider)}, {Number(pair.Centroid.Y, provider)}) {units}";
+    }
+
+    // Significant figures adapt to scale: a positive sliver must never read as zero.
+    public static string Number(double value, IFormatProvider provider = null) =>
+        value.ToString("G6", provider ?? CultureInfo.CurrentCulture);
+
+    public static double MarkerHalfSize(int deviceDpi) => 6.0 * deviceDpi / 96;
+    public static double HitRadius(int deviceDpi) => 10.0 * deviceDpi / 96;
+
+    /// <summary>
+    /// Projects cached centroids into a screen-pixel coordinate space. The pointer must
+    /// use that same space; view zoom never scales the DPI-adjusted hit radius.
+    /// Coincident or nearby markers return every matching pair in stable ID order.
+    /// </summary>
+    public static IReadOnlyList<PlateOverlapPair> HitTest(IEnumerable<PlateOverlapPair> pairs,
+        Func<Vector, Vector> worldToScreen, Vector pointer, int deviceDpi)
+    {
+        var radius = HitRadius(deviceDpi);
+        return pairs.Where(pair =>
+        {
+            var center = worldToScreen(pair.Centroid);
+            var dx = pointer.X - center.X;
+            var dy = pointer.Y - center.Y;
+            return dx * dx + dy * dy <= radius * radius;
+        }).OrderBy(pair => pair.PartAId).ThenBy(pair => pair.PartBId).ToArray();
+    }
+}

OpenNest.Core/Diagnostics/OverlapReportState.cs

@@ -2,7 +2,7 @@ using System.Collections.Generic;
 
 namespace OpenNest.Diagnostics;
 
-public enum OverlapDisplayMode { Off, Areas }
+public enum OverlapDisplayMode { Off, Areas, Centroids, Both }
 public enum OverlapCheckStatus { NotChecked, Checking, Current, Incomplete, Failed, Canceled, Stale }
 
 /// <summary>UI-thread lifecycle policy, independent of workers, GDI and view transforms.</summary>
@@ -34,7 +34,8 @@ public sealed class OverlapReportState
     {
         Clear(OverlapCheckStatus.Checking);
         stamp = OverlapGeometryStamp.Capture(plate);
-        DisplayMode = OverlapDisplayMode.Areas;
+        if (DisplayMode == OverlapDisplayMode.Off)
+            DisplayMode = OverlapDisplayMode.Areas;
         return Generation;
     }
 

OpenNest.Core/Diagnostics/PlateOverlapAnalyzer.cs

@@ -150,14 +150,26 @@ public static class PlateOverlapAnalyzer
                     var result = Collision.Check(localA.Outer, localB.Outer, localA.Holes, localB.Holes);
                     if (!result.Overlaps)
                         continue;
-                    var regions = result.OverlapRegions.Select(region => new PlateOverlapRegion(
-                        region.Vertices.Select(point => point + origin),
-                        OverlapMaterial.Area(region.Vertices))).ToList();
-                    var area = regions.Sum(region => region.Area);
-                    if (!double.IsFinite(area) || area <= 0)
-                        throw new ArithmeticException("Overlap area is not finite and positive.");
+                    // Evaluate every hole-subtracted fragment before restoring world space.
+                    // A failed moment must make this pair incomplete, never an origin marker.
+                    var moments = new List<PolygonAreaMoments>();
+                    var regions = new List<PlateOverlapRegion>();
+                    foreach (var region in result.OverlapRegions)
+                    {
+                        cancellationToken.ThrowIfCancellationRequested();
+                        if (!PolygonAreaMoments.TryCompute(region.Vertices, out var fragment))
+                            throw new ArithmeticException("Overlap fragment area moments are invalid.");
+                        moments.Add(fragment);
+                        regions.Add(new PlateOverlapRegion(region.Vertices.Select(point => point + origin),
+                            fragment.Area));
+                    }
+                    if (!PolygonAreaMoments.TryCombine(moments, out var combined))
+                        throw new ArithmeticException("Combined overlap area moments are invalid.");
+                    var centroid = combined.Centroid + origin;
+                    if (!OverlapMaterial.IsFinite(centroid))
+                        throw new ArithmeticException("Overlap centroid is not finite in world coordinates.");
                     pairs.Add(new PlateOverlapPair(a.Input.Id, b.Input.Id,
-                        a.Input.Name, b.Input.Name, regions));
+                        a.Input.Name, b.Input.Name, regions, centroid));
                 }
                 catch (Exception exception) when (IsGeometryFailure(exception))
                 {

OpenNest.Core/Diagnostics/PlateOverlapReport.cs

@@ -25,7 +25,7 @@ public sealed class PlateOverlapPair
     private readonly Box bounds;
 
     internal PlateOverlapPair(int partAId, int partBId, string partAName, string partBName,
-        List<PlateOverlapRegion> regions)
+        List<PlateOverlapRegion> regions, Vector centroid)
     {
         PartAId = partAId;
         PartBId = partBId;
@@ -33,6 +33,7 @@ public sealed class PlateOverlapPair
         PartBName = partBName;
         Regions = regions.AsReadOnly();
         Area = regions.Sum(region => region.Area);
+        Centroid = centroid;
         var points = regions.SelectMany(region => region.Vertices).ToArray();
         var left = points.Min(point => point.X);
         var bottom = points.Min(point => point.Y);
@@ -47,6 +48,11 @@ public sealed class PlateOverlapPair
     /// <summary>Convex fragments, not connected islands; no mutable kernel polygons are exposed.</summary>
     public IReadOnlyList<PlateOverlapRegion> Regions { get; }
     public double Area { get; }
+    /// <summary>
+    /// Finite world-coordinate area centroid of all shared material, after hole subtraction.
+    /// This can lie outside disconnected or concave shared material. Returned by value.
+    /// </summary>
+    public Vector Centroid { get; }
     /// <summary>A fresh world-coordinate bounds copy.</summary>
     public Box Bounds => new(bounds.X, bounds.Y, bounds.Length, bounds.Width);
 }

OpenNest.Core/Geometry/PolygonAreaMoments.cs

@@ -0,0 +1,101 @@
+using System.Collections.Generic;
+
+namespace OpenNest.Geometry;
+
+/// <summary>
+/// Positive area and area centroid of a simple polygon, independent of winding.
+/// Moments are evaluated about a nearby origin rather than the world origin.
+/// </summary>
+public readonly struct PolygonAreaMoments
+{
+    private PolygonAreaMoments(double area, Vector centroid)
+    {
+        Area = area;
+        Centroid = centroid;
+    }
+
+    public double Area { get; }
+    public Vector Centroid { get; }
+
+    /// <summary>
+    /// Accepts an open vertex list or an exactly repeated closing vertex. Returns false
+    /// for degenerate or nonfinite moments; does not validate polygon topology.
+    /// </summary>
+    public static bool TryCompute(IReadOnlyList<Vector> vertices, out PolygonAreaMoments moments)
+    {
+        moments = default;
+        if (vertices == null || vertices.Count < 3)
+            return false;
+        foreach (var point in vertices)
+            if (!IsFinite(point))
+                return false;
+
+        var origin = vertices[0];
+        var count = vertices.Count;
+        if (vertices[count - 1].X == origin.X && vertices[count - 1].Y == origin.Y)
+            count--;
+        if (count < 3)
+            return false;
+
+        var twiceArea = 0.0;
+        var momentX = 0.0;
+        var momentY = 0.0;
+        // The closing edges meet the local origin and contribute zero. The signed
+        // triangle fan also handles concavity without averaging polygon vertices.
+        for (var i = 1; i + 1 < count; i++)
+        {
+            var a = vertices[i] - origin;
+            var b = vertices[i + 1] - origin;
+            var cross = a.X * b.Y - a.Y * b.X;
+            twiceArea += cross;
+            momentX += (a.X + b.X) * cross;
+            momentY += (a.Y + b.Y) * cross;
+        }
+
+        var area = System.Math.Abs(twiceArea) * 0.5;
+        if (!double.IsFinite(area) || area <= 0
+            || !double.IsFinite(momentX) || !double.IsFinite(momentY))
+            return false;
+        // Dividing signed moments by signed area cancels the winding, while Area
+        // stays positive so independently wound fragments always add material.
+        var centroid = origin + new Vector(momentX / twiceArea / 3, momentY / twiceArea / 3);
+        if (!IsFinite(centroid))
+            return false;
+        moments = new PolygonAreaMoments(area, centroid);
+        return true;
+    }
+
+    /// <summary>
+    /// Combines nonoverlapping, already hole-subtracted fragments using positive area
+    /// weights and another local origin. The centroid may lie outside the material.
+    /// Empty input or any invalid fragment fails the entire result.
+    /// </summary>
+    public static bool TryCombine(IEnumerable<PolygonAreaMoments> fragments, out PolygonAreaMoments moments)
+    {
+        moments = default;
+        if (fragments == null)
+            return false;
+        var area = 0.0;
+        var origin = Vector.Zero;
+        var firstMoment = Vector.Zero;
+        foreach (var fragment in fragments)
+        {
+            if (!double.IsFinite(fragment.Area) || fragment.Area <= 0 || !IsFinite(fragment.Centroid))
+                return false;
+            if (area == 0)
+                origin = fragment.Centroid;
+            firstMoment += (fragment.Centroid - origin) * fragment.Area;
+            area += fragment.Area;
+        }
+
+        if (!double.IsFinite(area) || area <= 0 || !IsFinite(firstMoment))
+            return false;
+        var centroid = origin + firstMoment / area;
+        if (!IsFinite(centroid))
+            return false;
+        moments = new PolygonAreaMoments(area, centroid);
+        return true;
+    }
+
+    private static bool IsFinite(Vector point) => double.IsFinite(point.X) && double.IsFinite(point.Y);
+}