feat: add Box.Translate and improve NFP/IFP geometry APIs

Add immutable Translate methods to Box. Make NoFitPolygon
ToClipperPath/FromClipperPath public with optional offset parameter.
Refactor InnerFitPolygon.ComputeFeasibleRegion to accept PathsD
directly, letting Clipper2 handle implicit union. Add UpdateBounds
calls after polygon construction.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Core/Geometry/Box.cs

@@ -74,6 +74,16 @@ namespace OpenNest.Geometry
             Location += voffset;
         }
 
+        public Box Translate(double x, double y)
+        {
+            return new Box(X + x, Y + y, Width, Length);
+        }
+
+        public Box Translate(Vector offset)
+        {
+            return new Box(X + offset.X, Y + offset.Y, Width, Length);
+        }
+
         public double Left
         {
             get { return X; }

OpenNest.Core/Geometry/InnerFitPolygon.cs

@@ -52,6 +52,7 @@ namespace OpenNest.Geometry
             result.Vertices.Add(new Vector(ifpRight, ifpTop));
             result.Vertices.Add(new Vector(ifpLeft, ifpTop));
             result.Close();
+            result.UpdateBounds();
 
             return result;
         }
@@ -62,36 +63,20 @@ namespace OpenNest.Geometry
         /// Returns the polygon representing valid placement positions, or an empty
         /// polygon if no valid position exists.
         /// </summary>
-        public static Polygon ComputeFeasibleRegion(Polygon ifp, Polygon[] nfps)
+        public static Polygon ComputeFeasibleRegion(Polygon ifp, PathsD nfpPaths)
         {
             if (ifp.Vertices.Count < 3)
                 return new Polygon();
 
-            if (nfps == null || nfps.Length == 0)
+            if (nfpPaths == null || nfpPaths.Count == 0)
                 return ifp;
 
             var ifpPath = NoFitPolygon.ToClipperPath(ifp);
             var ifpPaths = new PathsD { ifpPath };
 
-            // Union all NFPs.
-            var nfpPaths = new PathsD();
-
-            foreach (var nfp in nfps)
-            {
-                if (nfp.Vertices.Count >= 3)
-                {
-                    var path = NoFitPolygon.ToClipperPath(nfp);
-                    nfpPaths.Add(path);
-                }
-            }
-
-            if (nfpPaths.Count == 0)
-                return ifp;
-
-            var nfpUnion = Clipper.Union(nfpPaths, FillRule.NonZero);
-
-            // Subtract the NFP union from the IFP.
-            var feasible = Clipper.Difference(ifpPaths, nfpUnion, FillRule.NonZero);
+            // Subtract the NFPs from the IFP.
+            // Clipper2 handles the implicit union of the clip paths.
+            var feasible = Clipper.Difference(ifpPaths, nfpPaths, FillRule.NonZero);
 
             if (feasible.Count == 0)
                 return new Polygon();
@@ -118,6 +103,25 @@ namespace OpenNest.Geometry
             return bestPath != null ? NoFitPolygon.FromClipperPath(bestPath) : new Polygon();
         }
 
+        /// <summary>
+        /// Computes the feasible region for placing a part given already-placed parts.
+        /// (Legacy overload for backward compatibility).
+        /// </summary>
+        public static Polygon ComputeFeasibleRegion(Polygon ifp, Polygon[] nfps)
+        {
+            if (nfps == null || nfps.Length == 0)
+                return ifp;
+
+            var nfpPaths = new PathsD(nfps.Length);
+            foreach (var nfp in nfps)
+            {
+                if (nfp.Vertices.Count >= 3)
+                    nfpPaths.Add(NoFitPolygon.ToClipperPath(nfp));
+            }
+
+            return ComputeFeasibleRegion(ifp, nfpPaths);
+        }
+
         /// <summary>
         /// Finds the bottom-left-most point on a polygon boundary.
         /// "Bottom-left" means: minimize Y first, then minimize X.

OpenNest.Core/Geometry/NoFitPolygon.cs

@@ -250,9 +250,9 @@ namespace OpenNest.Geometry
         }
 
         /// <summary>
-        /// Converts an OpenNest Polygon to a Clipper2 PathD.
+        /// Converts an OpenNest Polygon to a Clipper2 PathD, with an optional offset.
         /// </summary>
-        internal static PathD ToClipperPath(Polygon polygon)
+        public static PathD ToClipperPath(Polygon polygon, Vector offset = default)
         {
             var path = new PathD();
             var verts = polygon.Vertices;
@@ -263,7 +263,7 @@ namespace OpenNest.Geometry
                 n--;
 
             for (var i = 0; i < n; i++)
-                path.Add(new PointD(verts[i].X, verts[i].Y));
+                path.Add(new PointD(verts[i].X + offset.X, verts[i].Y + offset.Y));
 
             return path;
         }
@@ -271,7 +271,7 @@ namespace OpenNest.Geometry
         /// <summary>
         /// Converts a Clipper2 PathD to an OpenNest Polygon.
         /// </summary>
-        internal static Polygon FromClipperPath(PathD path)
+        public static Polygon FromClipperPath(PathD path)
         {
             var polygon = new Polygon();
 
@@ -279,6 +279,7 @@ namespace OpenNest.Geometry
                 polygon.Vertices.Add(new Vector(pt.x, pt.y));
 
             polygon.Close();
+            polygon.UpdateBounds();
             return polygon;
         }
     }