feat(io): add title block region detection with corner/edge scoring (phase 3)

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

OpenNest.IO/TitleBlockDetector.cs

@@ -19,6 +19,8 @@ namespace OpenNest.IO
             var flagged = new HashSet<Guid>();
             DetectByLayerName(entities, flagged);
             DetectBorder(entities, flagged);
+            if (document != null)
+                DetectTitleBlockRegion(entities, document, flagged);
             return flagged;
         }
 
@@ -126,5 +128,185 @@ namespace OpenNest.IO
                     flagged.Add(line.Id);
             }
         }
+
+        private static void DetectTitleBlockRegion(List<Entity> entities, CadDocument document, HashSet<Guid> flagged)
+        {
+            var textPositions = ExtractTextPositions(document);
+            if (textPositions.Count < 3) return;
+
+            var unflagged = entities.Where(e => !flagged.Contains(e.Id)).ToList();
+            if (unflagged.Count == 0) return;
+
+            var bounds = entities.GetBoundingBox();
+            if (bounds == null || bounds.Area() < OpenNest.Math.Tolerance.Epsilon) return;
+
+            var bestRegion = FindBestTitleBlockRegion(bounds, textPositions, unflagged);
+            if (bestRegion == null) return;
+
+            var initiallyInside = unflagged.Where(e => {
+                var c = EntityCenter(e);
+                return c.HasValue && RegionContains(bestRegion, c.Value);
+            }).ToList();
+
+            var expandedBounds = initiallyInside.Count > 0 ? initiallyInside.GetBoundingBox() : null;
+
+            foreach (var entity in unflagged)
+            {
+                var center = EntityCenter(entity);
+                if (!center.HasValue) continue;
+                if (RegionContains(bestRegion, center.Value)
+                    || (expandedBounds != null && RegionContains(expandedBounds, center.Value)))
+                    flagged.Add(entity.Id);
+            }
+        }
+
+        private static List<Vector> ExtractTextPositions(CadDocument document)
+        {
+            var positions = new List<Vector>();
+            foreach (var entity in document.Entities)
+            {
+                switch (entity)
+                {
+                    case ACadSharp.Entities.MText mtext:
+                        positions.Add(new Vector(mtext.InsertPoint.X, mtext.InsertPoint.Y));
+                        break;
+                    case ACadSharp.Entities.TextEntity text:
+                        var pt = text.HorizontalAlignment != 0 || text.VerticalAlignment != 0
+                            ? text.AlignmentPoint : text.InsertPoint;
+                        positions.Add(new Vector(pt.X, pt.Y));
+                        break;
+                }
+            }
+            return positions;
+        }
+
+        private static Box FindBestTitleBlockRegion(Box bounds, List<Vector> textPositions, List<Entity> entities)
+        {
+            var candidates = GenerateCandidateRegions(bounds);
+            Box bestRegion = null;
+            var bestScore = 0.0;
+
+            var openLines = FindOpenLines(entities);
+
+            foreach (var region in candidates)
+            {
+                var textCount = textPositions.Count(p => RegionContains(region, p));
+                if (textCount < 3) continue;
+
+                var openLineCount = openLines.Count(l => RegionContains(region, l.MidPoint));
+
+                var area = region.Area();
+                if (area < OpenNest.Math.Tolerance.Epsilon) continue;
+
+                var score = (double)textCount + openLineCount * 0.5;
+
+                var regionCenterX = (region.Left + region.Right) / 2;
+                var regionCenterY = (region.Bottom + region.Top) / 2;
+                if (regionCenterX > bounds.Center.X) score *= 1.3;
+                if (regionCenterY < bounds.Center.Y) score *= 1.3;
+
+                if (score > bestScore)
+                {
+                    bestScore = score;
+                    bestRegion = region;
+                }
+            }
+
+            return bestRegion;
+        }
+
+        private static List<Box> GenerateCandidateRegions(Box bounds)
+        {
+            var regions = new List<Box>();
+            var fractions = new[] { 0.25, 0.333, 0.5 };
+
+            foreach (var fx in fractions)
+            {
+                foreach (var fy in fractions)
+                {
+                    var w = bounds.Length * fx;
+                    var h = bounds.Width * fy;
+
+                    regions.Add(new Box(bounds.Right - w, bounds.Bottom, w, h));
+                    regions.Add(new Box(bounds.Left, bounds.Bottom, w, h));
+                    regions.Add(new Box(bounds.Right - w, bounds.Top - h, w, h));
+                    regions.Add(new Box(bounds.Left, bounds.Top - h, w, h));
+                }
+            }
+
+            foreach (var fy in fractions)
+            {
+                var h = bounds.Width * fy;
+                regions.Add(new Box(bounds.Left, bounds.Bottom, bounds.Length, h));
+            }
+
+            foreach (var fx in fractions)
+            {
+                var w = bounds.Length * fx;
+                regions.Add(new Box(bounds.Right - w, bounds.Bottom, w, bounds.Width));
+            }
+
+            return regions;
+        }
+
+        private static List<Line> FindOpenLines(List<Entity> entities)
+        {
+            var endpointUsers = new Dictionary<long, int>();
+
+            foreach (var entity in entities)
+            {
+                foreach (var ep in GetEntityEndpoints(entity))
+                {
+                    var key = QuantizePoint(ep);
+                    endpointUsers[key] = endpointUsers.GetValueOrDefault(key) + 1;
+                }
+            }
+
+            var openLines = new List<Line>();
+            foreach (var line in entities.OfType<Line>())
+            {
+                var startKey = QuantizePoint(line.StartPoint);
+                var endKey = QuantizePoint(line.EndPoint);
+
+                if (endpointUsers.GetValueOrDefault(startKey) <= 1 || endpointUsers.GetValueOrDefault(endKey) <= 1)
+                    openLines.Add(line);
+            }
+
+            return openLines;
+        }
+
+        private static List<Vector> GetEntityEndpoints(Entity entity)
+        {
+            return entity switch
+            {
+                Line line => new List<Vector> { line.StartPoint, line.EndPoint },
+                Arc arc => new List<Vector> { arc.StartPoint(), arc.EndPoint() },
+                _ => new List<Vector>()
+            };
+        }
+
+        private static long QuantizePoint(Vector pt)
+        {
+            var qx = (long)(pt.X * 1000);
+            var qy = (long)(pt.Y * 1000);
+            return qx * 100000000L + qy;
+        }
+
+        private static Vector? EntityCenter(Entity entity)
+        {
+            return entity switch
+            {
+                Line line => line.MidPoint,
+                Arc arc => arc.Center,
+                Circle circle => circle.Center,
+                _ => null
+            };
+        }
+
+        private static bool RegionContains(Box box, Vector pt)
+        {
+            return pt.X >= box.Left && pt.X <= box.Right
+                && pt.Y >= box.Bottom && pt.Y <= box.Top;
+        }
     }
 }

OpenNest.Tests/IO/TitleBlockDetectorTests.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using CSMath;
 using OpenNest.Geometry;
 using OpenNest.IO;
 using Xunit;
@@ -148,5 +149,97 @@ namespace OpenNest.Tests.IO
 
             Assert.Contains(entities[0].Id, result);
         }
+
+        [Fact]
+        public void DetectTitleBlock_FlagsEntitiesInTextDenseCorner()
+        {
+            var partLine1 = new Line(5, 70, 25, 120) { Layer = new Layer("0") };
+            var partLine2 = new Line(25, 120, 45, 70) { Layer = new Layer("0") };
+            var partLine3 = new Line(45, 70, 5, 70) { Layer = new Layer("0") };
+
+            var tbLines = new List<Entity>();
+            for (var x = 50; x <= 85; x += 5)
+                tbLines.Add(new Line(x, 0, x, 30) { Layer = new Layer("0") });
+            for (var y = 0; y <= 30; y += 5)
+                tbLines.Add(new Line(50, y, 85, y) { Layer = new Layer("0") });
+
+            var entities = new List<Entity> { partLine1, partLine2, partLine3 };
+            entities.AddRange(tbLines);
+
+            var doc = BuildDocWithTexts(
+                (60, 5, "TITLE: Test Part"),
+                (60, 10, "DWG NO: 12345"),
+                (60, 15, "SCALE: 1:1"),
+                (60, 20, "REV: A"),
+                (60, 25, "MATERIAL: STEEL"));
+
+            var result = TitleBlockDetector.Detect(entities, doc);
+
+            foreach (var tb in tbLines)
+                Assert.Contains(tb.Id, result);
+            Assert.DoesNotContain(partLine1.Id, result);
+            Assert.DoesNotContain(partLine2.Id, result);
+            Assert.DoesNotContain(partLine3.Id, result);
+        }
+
+        [Fact]
+        public void DetectTitleBlock_NoFalsePositivesWithoutText()
+        {
+            var entities = new List<Entity>
+            {
+                new Line(30, 40, 50, 90) { Layer = new Layer("0") },
+                new Line(50, 90, 70, 40) { Layer = new Layer("0") },
+                new Line(70, 40, 30, 40) { Layer = new Layer("0") },
+            };
+
+            var result = TitleBlockDetector.Detect(entities, null);
+
+            Assert.Empty(result);
+        }
+
+        [Fact]
+        public void DetectTitleBlock_BottomEdgeStrip()
+        {
+            var partLine = new Line(20, 40, 80, 40) { Layer = new Layer("0") };
+
+            var tbLines = new List<Entity>();
+            for (var x = 0; x <= 100; x += 10)
+                tbLines.Add(new Line(x, 0, x, 20) { Layer = new Layer("0") });
+            for (var y = 0; y <= 20; y += 5)
+                tbLines.Add(new Line(0, y, 100, y) { Layer = new Layer("0") });
+
+            var entities = new List<Entity> { partLine };
+            entities.AddRange(tbLines);
+
+            var doc = BuildDocWithTexts(
+                (10, 5, "TITLE"),
+                (30, 5, "DWG NO"),
+                (50, 5, "SCALE"),
+                (70, 5, "REV"),
+                (90, 5, "DATE"));
+
+            var result = TitleBlockDetector.Detect(entities, doc);
+
+            foreach (var tb in tbLines)
+                Assert.Contains(tb.Id, result);
+            Assert.DoesNotContain(partLine.Id, result);
+        }
+
+        private static ACadSharp.CadDocument BuildDocWithTexts(
+            params (double x, double y, string value)[] texts)
+        {
+            var doc = new ACadSharp.CadDocument();
+            foreach (var (x, y, value) in texts)
+            {
+                var mtext = new ACadSharp.Entities.MText
+                {
+                    InsertPoint = new XYZ(x, y, 0),
+                    Value = value,
+                    Height = 2.0
+                };
+                doc.Entities.Add(mtext);
+            }
+            return doc;
+        }
     }
 }