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;
+        }
     }
 }