Fix numerical stability for almost parallel lines, fixes #287

tdewolff · Apr 15, 2024 · 9df26aa · 9df26aa
1 parent e923d93
commit 9df26aa
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Showing 2 changed files with 19 additions and 6 deletions.
diff --git a/path_intersection_test.go b/path_intersection_test.go
@@ -816,8 +816,20 @@ func TestSelfIntersections(t *testing.T) {
 		//{"L10 10L10 0L0 10z", Intersections{ {Point{5.0, 5.0}, 1, 3, 0.5, 0.5, 0.25 * math.Pi, 0.75 * math.Pi, BintoA, NoParallel, false},
 		//}},
 
-		/// bugs
-		{"M3.512162397982181 1.239754268684486L3.3827323986701674 1.1467946944092953L3.522449858001167 1.2493787337129587A0.21166666666666667 0.21166666666666667 0 0 1 3.5121623979821806 1.2397542686844856z", []PathIntersection{}},
+		// parallel segment
+		{"L10 0L5 0L15 0", []PathIntersection{
+			{Point{5.0, 0.0}, 1, 0.5, 0.0, false, true, false},
+			{Point{10.0, 0.0}, 3, 0.5, 0.0, false, true, false},
+		}},
+		{"M-0.1997406229376793 296.9999999925494L-0.1997406229376793 158.88740153238177L-0.19974062293732664 158.8874019079834L-0.19999999999964735 20.77454766193328", []PathIntersection{
+			{Point{-0.1997406229376793, 158.88740172019808}, 1, 0.9999999986401219, 270.0 * math.Pi / 180.0, true, false, false},
+			{Point{-0.1997406229376793, 158.88740172019808}, 3, 1.359651237533596e-09, 269.9998923980606 * math.Pi / 180.0, false, false, false},
+		}}, // #287
+
+		// bugs
+		{"M3.512162397982181 1.239754268684486L3.3827323986701674 1.1467946944092953L3.522449858001167 1.2493787337129587A0.21166666666666667 0.21166666666666667 0 0 1 3.5121623979821806 1.2397542686844856z", []PathIntersection{
+			// TODO: add
+		}},
 	}
 	for _, tt := range tts {
 		t.Run(fmt.Sprint(tt.p), func(t *testing.T) {

diff --git a/path_intersection_util.go b/path_intersection_util.go
@@ -650,6 +650,7 @@ func pathIntersections(p, q *Path, withTangents, withParallelTangents bool) ([]P
 								})
 							}
 						} else {
+
 							// intersection is parallel
 							m := 0
 							for {
@@ -1031,13 +1032,12 @@ func intersectionLineLine(zs Intersections, a0, a1, b0, b1 Point) Intersections
 
 	da := a1.Sub(a0)
 	db := b1.Sub(b0)
-	div := da.PerpDot(db)
-	if Equal(div, 0.0) {
+	angle0 := da.Angle()
+	angle1 := db.Angle()
+	if angleEqual(angle0, angle1) || angleEqual(angle0, angle1+math.Pi) {
 		// parallel
 		if Equal(da.PerpDot(b1.Sub(a0)), 0.0) {
 			// aligned, rotate to x-axis
-			angle0 := da.Angle()
-			angle1 := db.Angle()
 			a := a0.Rot(-angle0, Point{}).X
 			b := a1.Rot(-angle0, Point{}).X
 			c := b0.Rot(-angle0, Point{}).X
@@ -1071,6 +1071,7 @@ func intersectionLineLine(zs Intersections, a0, a1, b0, b1 Point) Intersections
 		return zs
 	}
 
+	div := da.PerpDot(db)
 	ta := db.PerpDot(a0.Sub(b0)) / div
 	tb := da.PerpDot(a0.Sub(b0)) / div
 	if Interval(ta, 0.0, 1.0) && Interval(tb, 0.0, 1.0) {