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fix: correct NFP polygon computation and inflation direction

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Three bugs fixed in NfpSlideStrategy pipeline:

1. NoFitPolygon.Reflect() incorrectly reversed vertex order. Point
   reflection (negating both axes) is a 180° rotation that preserves
   winding — the Reverse() call was converting CCW to CW, producing
   self-intersecting bowtie NFPs.

2. PolygonHelper inflation used OffsetSide.Left which is inward for
   CCW perimeters. Changed to OffsetSide.Right for outward inflation
   so NFP boundary positions give properly-spaced part placements.

3. Removed incorrect correction vector — same-drawing pairs have
   identical polygon-to-part offsets that cancel out in the NFP
   displacement.

Also refactored NfpSlideStrategy to be immutable (removed mutable
cache fields, single constructor with required data, added Create
factory method). BestFitFinder remains on RotationSlideStrategy
as default.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
AJ Isaacs
2026-03-20 23:24:04 -04:00
parent 38dcaf16d3
commit 7f96d632f3
5 changed files with 181 additions and 70 deletions
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OpenNest.Engine/BestFit/PolygonHelper.cs
+15 -19
View File
@@ -22,13 +22,10 @@ namespace OpenNest.Engine.BestFit
if (perimeter == null)
return new PolygonExtractionResult(null, Vector.Zero);
// Compute the perimeter bounding box before inflation for coordinate correction.
perimeter.UpdateBounds();
var perimeterBb = perimeter.BoundingBox;
// Inflate by half-spacing if spacing is non-zero.
// OffsetSide.Right = outward for CCW perimeters (standard for outer contours).
var inflated = halfSpacing > 0
? (perimeter.OffsetEntity(halfSpacing, OffsetSide.Left) as Shape ?? perimeter)
? (perimeter.OffsetEntity(halfSpacing, OffsetSide.Right) as Shape ?? perimeter)
: perimeter;
// Convert to polygon with circumscribed arcs for tight nesting.
@@ -37,22 +34,18 @@ namespace OpenNest.Engine.BestFit
if (polygon.Vertices.Count < 3)
return new PolygonExtractionResult(null, Vector.Zero);
// Compute correction: difference between program origin and perimeter origin.
// Part.CreateAtOrigin normalizes to program bbox; polygon normalizes to perimeter bbox.
var programBb = drawing.Program.BoundingBox();
var correction = new Vector(
perimeterBb.Left - programBb.Location.X,
perimeterBb.Bottom - programBb.Location.Y);
// Normalize: move reference point to origin.
// Normalize: move polygon to origin.
polygon.UpdateBounds();
var bb = polygon.BoundingBox;
polygon.Offset(-bb.Left, -bb.Bottom);
return new PolygonExtractionResult(polygon, correction);
// No correction needed: BestFitFinder always pairs the same drawing with
// itself, so the polygon-to-part offset is identical for both parts and
// cancels out in the NFP displacement.
return new PolygonExtractionResult(polygon, Vector.Zero);
}
public static Polygon RotatePolygon(Polygon polygon, double angle)
public static Polygon RotatePolygon(Polygon polygon, double angle, bool reNormalize = true)
{
if (angle.IsEqualTo(0))
return polygon;
@@ -68,10 +61,13 @@ namespace OpenNest.Engine.BestFit
v.X * sin + v.Y * cos));
}
// Re-normalize to origin.
result.UpdateBounds();
var bb = result.BoundingBox;
result.Offset(-bb.Left, -bb.Bottom);
if (reNormalize)
{
// Re-normalize to origin.
result.UpdateBounds();
var bb = result.BoundingBox;
result.Offset(-bb.Left, -bb.Bottom);
}
return result;
}