Keep non-intersection subpaths as-in, without flattening, but X-monot…

…one, see #290

path_intersection.go

@@ -168,9 +168,8 @@ func (p *Path) Settle(fillRule FillRule) *Path {
 
 	// zp is an list of even length where each ith intersections is a pseudo-vertex of the ith+len/2
 	zp, zq := pathIntersections(p, nil, false, false)
-	if 0 < len(zp) {
-		ps = p.Split() // otherwise, keep unflattened path
-	}
+	psOrig := ps
+	ps = p.Split()
 	//for i, z := range zp {
 	//	fmt.Println(i, z)
 	//}
@@ -246,6 +245,20 @@ func (p *Path) Settle(fillRule FillRule) *Path {
 			continue // consists solely of MoveTo and Close
 		}
 
+		j1 := j0
+		for _, z := range zp[j0:] {
+			if segs[i] <= z.Seg {
+				break
+			}
+			j1++
+		}
+		hasIntersections := j0 != j1
+
+		if !hasIntersections {
+			// use unflattened path when subpath has no intersections, but make sure it is XMonotone
+			pi = psOrig[i].XMonotone()
+		}
+
 		// Find the left-most path segment coordinate for each subpath, we thus know that to the
 		// right of the coordinate the path is filled and that it is an outer ring. If the path
 		// runs counter clock-wise at the coordinate, the LHS is filled, otherwise it runs
@@ -282,14 +295,7 @@ func (p *Path) Settle(fillRule FillRule) *Path {
 		parentWindings := leftmostWindings(i, ps, pos.X, pos.Y)
 
 		// find the intersections for the subpath
-		j1 := j0
-		for _, z := range zp[j0:] {
-			if segs[i] <= z.Seg {
-				break
-			}
-			j1++
-		}
-		if j0 == j1 {
+		if !hasIntersections {
 			// subpath has no intersections
 			winding := 1
 			if !ccw {
@@ -402,6 +408,7 @@ func (p *Path) Settle(fillRule FillRule) *Path {
 		}
 		ring++
 	}
+	// TODO: undo X-Monotone to give a more optimal path?
 	return R.Append(simple).Append(open)
 }
 

path_intersection_test.go

@@ -959,6 +959,7 @@ func TestPathSettle(t *testing.T) {
 		//{NonZero, "L2 0L2 2L0 2L0 1L-1 2L-2 2L-1 2L0 1z", ""}, // parallel left-most endpoint
 		//{NonZero, "L0 1L-1 2L0 1z", ""},                       // all parallel
 		{NonZero, "M1 0L1 2.1L1.1 2.1L1.1 2L0 2L0 3L2 3L2 1L5 1L5 2L5.1 2.1L5.1 1.9L5 2L5 3L6 3L6 0z", "M5 1L2 1L2 3L0 3L0 2L1 2L1 0L6 0L6 3L5 3z"}, // CCW open first leg for CW path
+		{Positive, "M4.428086304186892 0.375A0.375 0.375 0 0 1 4.428086304186892 -0.375L6.428086304186892 -0.375A0.375 0.375 0 0 1 6.428086304186892 0.375z", "M4.428086304186892 0.375A0.375 0.375 0 0 1 4.053086304186892 4.592425496802568e-17A0.375 0.375 0 0 1 4.428086304186892 -0.375L6.428086304186892 -0.375A0.375 0.375 0 0 1 6.803086304186892 -9.184850993605136e-17A0.375 0.375 0 0 1 6.428086304186892 0.375z"}, // two arcs as leftmost point
 
 		// example from Subramaniam's thesis
 		{NonZero, "L5.5 10L4.5 10L9 1.5L1 8L9 8L1.6 2L3 1L5 7L8 0z", "M3.349892008639309 6.090712742980562L0 0L8 0L6.479452054794521 3.547945205479452L9 1.5L6.592324805339266 6.047830923248053L9 8L5.5588235294117645 8L4.990463215258855 9.073569482288828L4.3999999999999995 8L1 8L3.349892008639309 6.090712742980561zM3.9753086419753085 3.9259259259259265L3 1L1.6 2L3.975308641975309 3.925925925925927zM4.990463215258855 9.073569482288828L5.5 10L4.5 10L4.990463215258855 9.073569482288828z"},