update

tests/TraceCad.Tests/GeometryTests.cs

@@ -14,6 +14,79 @@ public sealed class GeometryTests
         Assert.Equal(5.0, line.Length, 9);
     }
 
+    [Fact]
+    public void ParallelConstraintPreservesTargetLengthAndMatchesReferenceDirection()
+    {
+        var reference = new LineEntity(Guid.NewGuid(), Layer.Cut.Name, new Point2(0, 0), new Point2(10, 0));
+        var target = new LineEntity(Guid.NewGuid(), Layer.Cut.Name, new Point2(0, 5), new Point2(0, 9));
+
+        var success = ConstraintGeometry.TryMakeParallel(reference, target, out var replacement);
+
+        Assert.True(success);
+        Assert.Equal(target.Length, replacement.Length, 9);
+        Assert.Equal(0.0, replacement.Start.Y - replacement.End.Y, 9);
+    }
+
+    [Fact]
+    public void ParallelDistanceMeasuresPerpendicularSpacing()
+    {
+        var first = new LineEntity(Guid.NewGuid(), Layer.Cut.Name, new Point2(0, 0), new Point2(10, 0));
+        var second = new LineEntity(Guid.NewGuid(), Layer.Cut.Name, new Point2(3, 7), new Point2(13, 7));
+
+        var success = ConstraintGeometry.TryMeasureParallelDistance(first, second, out var distance);
+
+        Assert.True(success);
+        Assert.Equal(7.0, distance, 9);
+    }
+
+    [Fact]
+    public void TangentConstraintMovesLineOntoNearestArcEndpointTangent()
+    {
+        var arc = new ArcEntity(Guid.NewGuid(), Layer.Cut.Name, new Point2(0, 0), 10, 0, 90, false);
+        var line = new LineEntity(Guid.NewGuid(), Layer.Cut.Name, new Point2(10.2, 0.1), new Point2(16.2, 2.1));
+
+        var success = ConstraintGeometry.TryMakeLineTangentToArc(line, arc, out var replacement);
+
+        Assert.True(success);
+        Assert.Equal(arc.StartPoint.X, replacement.Start.X, 9);
+        Assert.Equal(arc.StartPoint.Y, replacement.Start.Y, 9);
+        var direction = (replacement.End - replacement.Start).Normalized();
+        var tangent = GeometryHelpers.TangentAtAngle(arc.StartAngleDeg, arc.IsClockwise);
+        Assert.True(Math.Abs(direction.Dot(tangent)) > 0.999);
+    }
+
+    [Fact]
+    public void SolverAppliesDrivingRadiusDimension()
+    {
+        var document = SketchDocument.CreateDefault();
+        var arcId = Guid.NewGuid();
+        document.AddEntity(new ArcEntity(arcId, Layer.Cut.Name, new Point2(0, 0), 10, 0, 90, false));
+        document.AddConstraint(new SketchConstraint(Guid.NewGuid(), ConstraintType.Radius, new[] { arcId }, 25));
+
+        SketchConstraintSolver.Solve(document);
+
+        var arc = Assert.IsType<ArcEntity>(document.Entities.Single(entity => entity.Id == arcId));
+        Assert.Equal(25.0, arc.Radius, 9);
+    }
+
+    [Fact]
+    public void SolverAppliesDrivingParallelDistanceDimension()
+    {
+        var document = SketchDocument.CreateDefault();
+        var firstId = Guid.NewGuid();
+        var secondId = Guid.NewGuid();
+        document.AddEntity(new LineEntity(firstId, Layer.Cut.Name, new Point2(0, 0), new Point2(10, 0)));
+        document.AddEntity(new LineEntity(secondId, Layer.Cut.Name, new Point2(0, 2), new Point2(10, 2)));
+        document.AddConstraint(new SketchConstraint(Guid.NewGuid(), ConstraintType.Distance, new[] { firstId, secondId }, 7));
+
+        SketchConstraintSolver.Solve(document);
+
+        var first = Assert.IsType<LineEntity>(document.Entities.Single(entity => entity.Id == firstId));
+        var second = Assert.IsType<LineEntity>(document.Entities.Single(entity => entity.Id == secondId));
+        Assert.True(ConstraintGeometry.TryMeasureParallelDistance(first, second, out var distance));
+        Assert.Equal(7.0, distance, 9);
+    }
+
     [Fact]
     public void CircleFromThreePointsComputesCenterAndRadius()
     {
@@ -69,6 +142,34 @@ public sealed class GeometryTests
         Assert.False(success);
     }
 
+    [Fact]
+    public void ArcFromStartTangentAndEndPointMatchesRequestedTangent()
+    {
+        var success = GeometryHelpers.TryCreateArcFromStartTangentAndEndPoint(
+            new Point2(0, 0),
+            new Vector2(1, 0),
+            new Point2(10, 10),
+            new Point2(8, 2),
+            out var arc);
+
+        Assert.True(success);
+        var tangent = GeometryHelpers.TangentAtAngle(arc.StartAngleDeg, arc.IsClockwise);
+        Assert.True(tangent.Dot(new Vector2(1, 0)) > 0.999);
+    }
+
+    [Fact]
+    public void ArcFromStartTangentFailsWhenEndPointLiesOnTangentLine()
+    {
+        var success = GeometryHelpers.TryCreateArcFromStartTangentAndEndPoint(
+            new Point2(0, 0),
+            new Vector2(1, 0),
+            new Point2(10, 0),
+            null,
+            out _);
+
+        Assert.False(success);
+    }
+
     [Theory]
     [InlineData(360, 0)]
     [InlineData(-90, 270)]