feat(core): add CanonicalAngle helper for MBR-aligning angle

2026-04-20 08:57:03 -04:00
parent d2f9597b0c
commit 9a6b656e3c
2 changed files with 177 additions and 0 deletions
@@ -0,0 +1,78 @@
+using OpenNest.Converters;
+using OpenNest.Geometry;
+using System.Linq;
+
+namespace OpenNest
+{
+    /// <summary>
+    /// Computes the rotation that maps a drawing to its canonical (MBR-axis-aligned) frame.
+    /// Lives in OpenNest.Core so Drawing.Program setter can invoke it directly without
+    /// a circular dependency on OpenNest.Engine.
+    /// </summary>
+    public static class CanonicalAngle
+    {
+        /// <summary>Angles with |v| below this (radians) are snapped to 0.</summary>
+        public const double SnapToZero = 0.001;
+
+        /// <summary>
+        /// Derives the canonical angle from a pre-computed MBR. Used both by Compute (which
+        /// computes the MBR itself) and by PartClassifier (which already has one). Single formula
+        /// across both callers.
+        /// </summary>
+        public static double FromMbr(BoundingRectangleResult mbr)
+        {
+            if (mbr.Area <= OpenNest.Math.Tolerance.Epsilon)
+                return 0.0;
+
+            // The MBR edge angle can represent any of four equivalent orientations
+            // (edge-i, edge-i + π/2, edge-i + π, edge-i - π/2) depending on which hull
+            // edge the algorithm happened to pick. Normalize -mbr.Angle to the
+            // representative in [-π/4, π/4] so snap-to-zero works for inputs near
+            // ANY of the equivalent orientations.
+            var angle = -mbr.Angle;
+            const double halfPi = System.Math.PI / 2.0;
+            angle -= halfPi * System.Math.Round(angle / halfPi);
+
+            if (System.Math.Abs(angle) < SnapToZero)
+                return 0.0;
+
+            return angle;
+        }
+
+        public static double Compute(Drawing drawing)
+        {
+            if (drawing?.Program == null)
+                return 0.0;
+
+            var entities = ConvertProgram.ToGeometry(drawing.Program)
+                .Where(e => e.Layer != SpecialLayers.Rapid);
+
+            var shapes = ShapeBuilder.GetShapes(entities);
+            if (shapes.Count == 0)
+                return 0.0;
+
+            var perimeter = shapes[0];
+            var perimeterArea = perimeter.Area();
+            for (var i = 1; i < shapes.Count; i++)
+            {
+                var area = shapes[i].Area();
+                if (area > perimeterArea)
+                {
+                    perimeter = shapes[i];
+                    perimeterArea = area;
+                }
+            }
+
+            var polygon = perimeter.ToPolygonWithTolerance(0.1);
+            if (polygon == null || polygon.Vertices.Count < 3)
+                return 0.0;
+
+            var hull = ConvexHull.Compute(polygon.Vertices);
+            if (hull.Vertices.Count < 3)
+                return 0.0;
+
+            var mbr = RotatingCalipers.MinimumBoundingRectangle(hull);
+            return FromMbr(mbr);
+        }
+    }
+}