Merge pull request #86 from hfutrell/issue-81-contour-disappears

Issue 81 contour disappears
hfutrell · Jan 22, 2021 · 00b7870 · 00b7870
2 parents 38b45b3 + b57bff8
commit 00b7870
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Showing 2 changed files with 14 additions and 2 deletions.
diff --git a/BezierKit/BezierKitTests/UtilsTests.swift b/BezierKit/BezierKitTests/UtilsTests.swift
@@ -70,6 +70,17 @@ class UtilsTests: XCTestCase {
 //        XCTAssertEqual(filtered.first!, CGFloat(0.00149972), accuracy: 1.0e-4)
 //    }
 
+    func testDrootsCubicWorldIssue3() {
+        // this data causes issue #81 on GitHub
+        // discriminant is positive but very close to zero (8.46e-10)
+        // https://github.com/hfutrell/BezierKit/issues/81
+        let firstValue: CGFloat = -14.999127297400882
+        let otherValues: CGFloat = 0.00087270259911775838
+        let roots = drootsCubicTestHelper(firstValue, otherValues, otherValues, otherValues)
+        XCTAssertEqual(roots.count, 1)
+        XCTAssertEqual(roots[0], CGFloat(0.961251), accuracy: 1.0e-4)
+    }
+
     func testDrootsQuadratic() {
         let a: CGFloat = 0.36159566118413977
         let b: CGFloat = -3.2979288390483816

diff --git a/BezierKit/Library/Utils.swift b/BezierKit/Library/Utils.swift
@@ -187,7 +187,8 @@ internal class Utils {
         let q = (2 * a * a * a - 9 * a * b + 27 * c) / 27
         let q2 = q/2
         let discriminant = q2 * q2 + p * p * p / 27
-        if discriminant < -smallValue {
+        let tinyValue = 1.0e-14
+        if discriminant < -tinyValue {
             let r = sqrt(-p * p * p / 27)
             let t = -q / (2 * r)
             let cosphi = t < -1 ? -1 : t > 1 ? 1 : t
@@ -204,7 +205,7 @@ internal class Utils {
             if root3 > root2 {
                 callback(root3)
             }
-        } else if discriminant > smallValue {
+        } else if discriminant > tinyValue {
             let sd = sqrt(discriminant)
             let u1 = crt(-q2 + sd)
             let v1 = crt(q2 + sd)