Fix bug in windings for open paths, fixes #346

Author: tdewolff

path.go

@@ -10,9 +10,10 @@ import (
 	"strings"
 
 	"github.com/srwiley/scanx"
-	"github.com/tdewolff/parse/v2/strconv"
 	"golang.org/x/image/math/fixed"
 	"golang.org/x/image/vector"
+
+	"github.com/tdewolff/parse/v2/strconv"
 )
 
 // Tolerance is the maximum deviation from the original path in millimeters when e.g. flatting. Used for flattening in the renderers, font decorations, and path intersections.
@@ -872,7 +873,7 @@ func windings(zs []Intersection) (int, bool) {
 			if !z.Same {
 				n += d
 			}
-		} else {
+		} else if i+1 < len(zs) {
 			same := z.Same || zs[i+1].Same
 			if !same {
 				if z.Into() == zs[i+1].Into() {

path_intersection.go

@@ -16,8 +16,9 @@ import (
 var BentleyOttmannEpsilon = 1e-8
 
 // RayIntersections returns the intersections of a path with a ray starting at (x,y) to (∞,y).
-// An intersection is tangent only when it is at (x,y), i.e. the start of the ray. Intersections
-// are sorted along the ray. This function runs in O(n) with n the number of path segments.
+// An intersection is tangent only when it is at (x,y), i.e. the start of the ray. The parameter T
+// along the ray is zero at the start but NaN otherwise. Intersections are sorted along the ray.
+// This function runs in O(n) with n the number of path segments.
 func (p *Path) RayIntersections(x, y float64) []Intersection {
 	var start, end Point
 	var zs []Intersection

path_test.go

@@ -10,12 +10,13 @@ import (
 	"testing"
 
 	"github.com/srwiley/scanx"
-	"github.com/tdewolff/test"
 	"golang.org/x/image/vector"
 	"gonum.org/v1/plot"
 	"gonum.org/v1/plot/plotter"
 	"gonum.org/v1/plot/vg"
 	"gonum.org/v1/plot/vg/draw"
+
+	"github.com/tdewolff/test"
 )
 
 func TestPathEmpty(t *testing.T) {
@@ -252,6 +253,10 @@ func TestPathCrossingsWindings(t *testing.T) {
 		{"L10 10L10 -10L-10 10L20 40L20 -40L-10 -10z", Point{0.0, 0.0}, 2, 0, true},
 		{"L10 10L10 -10L-10 10L20 40L20 -40L-10 -10z", Point{1.0, 0.0}, 2, -2, false},
 		{"L10 10L10 -10L-10 10L20 40L20 -40L-10 -10z", Point{-1.0, 0.0}, 4, 0, false},
+
+		// bugs
+		{"M0 35.43000000000029L0 385.82000000000016L11.819999999999709 397.6300000000001L185.03999999999996 397.6300000000001L188.97999999999956 393.7000000000003L196.85000000000036 385.8299999999999L196.85000000000036 19.68000000000029", Point{89.4930000000003, 19.68000000000019}, 0, 0, false}, // #346
+		{"M0 35.43000000000029L0 385.82000000000016L11.819999999999709 397.6300000000001L185.03999999999996 397.6300000000001L188.97999999999956 393.7000000000003L196.85000000000036 385.8299999999999L196.85000000000036 19.68000000000029", Point{89.4930000000003, 20}, 1, -1, false},               // #346
 	}
 	for _, tt := range tts {
 		t.Run(fmt.Sprint(tt.p, " at ", tt.pos), func(t *testing.T) {