fix(geometry): stabilize triangulation winding at large coordinates

2026-09-28 20:37:38 -04:00
parent 1f637ca43c
commit fb32d508f8
2 changed files with 75 additions and 7 deletions
@@ -0,0 +1,70 @@
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests.Geometry;
+
+public class CollisionTranslationTests
+{
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void Check_ContainedClockwisePolygonFarFromOriginDoesNotDependOnOperandOrder(bool swap)
+    {
+        var outer = Square(0, 0, 1e9);
+        var small = Square(999999998, 999999998, 1);
+        small.Reverse();
+
+        var result = swap ? Collision.Check(small, outer) : Collision.Check(outer, small);
+
+        Assert.True(result.Overlaps);
+        // Do not use Polygon.Area here: this test isolates triangulation, not that legacy API.
+        Assert.Equal(1, result.OverlapRegions.Sum(StableArea), 8);
+    }
+
+    [Fact]
+    public void Check_ClockwiseHoleFarFromOriginIsSubtracted()
+    {
+        var outer = Square(0, 0, 1e9);
+        var hole = Square(999999998, 999999998, 1);
+        hole.Reverse();
+        var insert = Square(999999998.25, 999999998.25, 0.5);
+
+        var result = Collision.Check(outer, insert, new List<Polygon> { hole });
+
+        Assert.False(result.Overlaps);
+        Assert.Empty(result.OverlapRegions);
+    }
+
+    [Theory]
+    [InlineData(1000000000)]
+    [InlineData(-1000000000)]
+    public void Triangulate_ClockwiseTranslatedUnitSquareHasFullArea(double offset)
+    {
+        var polygon = Square(offset, offset, 1);
+        polygon.Reverse();
+        var triangles = ConvexDecomposition.Triangulate(polygon);
+        Assert.Equal(2, triangles.Count);
+        Assert.Equal(1, triangles.Sum(StableArea), 8);
+    }
+
+    private static Polygon Square(double x, double y, double size)
+    {
+        var polygon = new Polygon();
+        polygon.Vertices.AddRange(new[] { new Vector(x, y), new Vector(x + size, y),
+            new Vector(x + size, y + size), new Vector(x, y + size), new Vector(x, y) });
+        polygon.UpdateBounds();
+        return polygon;
+    }
+
+    private static double StableArea(Polygon polygon)
+    {
+        var area = 0.0;
+        var origin = polygon.Vertices[0];
+        for (var i = 1; i + 1 < polygon.Vertices.Count; i++)
+        {
+            var a = polygon.Vertices[i] - origin;
+            var b = polygon.Vertices[i + 1] - origin;
+            area += a.X * b.Y - a.Y * b.X;
+        }
+        return System.Math.Abs(area) / 2;
+    }
+}