fixed a problem with closed paths and self intersecting polygons

added the readme example as a test

README.md

@@ -126,4 +126,5 @@ These features *should* work just like their HTML5 counterparts, but there are l
 # Missing features
 
 - globalCompositeOperation
+- imageSmoothingEnabled
 - textBaseline hanging and ideographic (currently work just like top and bottom)

canvas_test.go

@@ -584,3 +584,26 @@ func TestShadow(t *testing.T) {
 		cv.FillRect(50, 15, 30, 60)
 	})
 }
+
+func TestReadme(t *testing.T) {
+	run(t, func(cv *canvas.Canvas) {
+		w, h := 100.0, 100.0
+		cv.SetFillStyle("#000")
+		cv.FillRect(0, 0, w, h)
+
+		for r := 0.0; r < math.Pi*2; r += math.Pi * 0.1 {
+			cv.SetFillStyle(int(r*10), int(r*20), int(r*40))
+			cv.BeginPath()
+			cv.MoveTo(w*0.5, h*0.5)
+			cv.Arc(w*0.5, h*0.5, math.Min(w, h)*0.4, r, r+0.1*math.Pi, false)
+			cv.ClosePath()
+			cv.Fill()
+		}
+
+		cv.SetStrokeStyle("#FFF")
+		cv.SetLineWidth(10)
+		cv.BeginPath()
+		cv.Arc(w*0.5, h*0.5, math.Min(w, h)*0.4, 0, math.Pi*2, false)
+		cv.Stroke()
+	})
+}

path2d.go

@@ -82,18 +82,20 @@ func (p *Path2D) lineTo(x, y float64, checkSelfIntersection bool) {
 		newp.flags |= pathIsConvex
 	} else if prev.flags&pathIsConvex > 0 {
 		cuts := false
+		var cutPoint vec
 		if checkSelfIntersection && !Performance.IgnoreSelfIntersections {
 			b0, b1 := prev.pos, vec{x, y}
 			for i := 1; i < count; i++ {
 				a0, a1 := p.p[i-1].pos, p.p[i].pos
-				_, r1, r2 := lineIntersection(a0, a1, b0, b1)
+				var r1, r2 float64
+				cutPoint, r1, r2 = lineIntersection(a0, a1, b0, b1)
 				if r1 > 0 && r1 < 1 && r2 > 0 && r2 < 1 {
 					cuts = true
 					break
 				}
 			}
 		}
-		if cuts {
+		if cuts && !isSamePoint(cutPoint, vec{x, y}, samePointTolerance) {
 			newp.flags |= pathSelfIntersects
 		} else {
 			prev2 := &p.p[len(p.p)-3]
@@ -288,24 +290,39 @@ func (p *Path2D) Rect(x, y, w, h float64) {
 // func (p *Path2D) Ellipse(...) {
 // }
 
-func runSubPaths(path []pathPoint, fn func(subPath []pathPoint) bool) {
+func runSubPaths(path []pathPoint, close bool, fn func(subPath []pathPoint) bool) {
 	start := 0
 	for i, p := range path {
 		if p.flags&pathMove == 0 {
 			continue
 		}
 		if i >= start+3 {
-			if fn(path[start:i]) {
+			end := i
+			if runSubPath(path[start:end], close, fn) {
 				return
 			}
 		}
 		start = i
 	}
 	if len(path) >= start+3 {
-		fn(path[start:])
+		runSubPath(path[start:], close, fn)
 	}
 }
 
+func runSubPath(path []pathPoint, close bool, fn func(subPath []pathPoint) bool) bool {
+	if !close || path[0].pos == path[len(path)-1].pos {
+		return fn(path)
+	}
+
+	var buf [64]pathPoint
+	path2 := Path2D{
+		p:    append(buf[:0], path...),
+		move: path[0].pos,
+	}
+	path2.lineTo(path[0].pos[0], path[0].pos[1], true)
+	return fn(path2.p)
+}
+
 type pathRule uint8
 
 // Path rule constants. See https://en.wikipedia.org/wiki/Nonzero-rule
@@ -319,7 +336,7 @@ const (
 // to the given rule
 func (p *Path2D) IsPointInPath(x, y float64, rule pathRule) bool {
 	inside := false
-	runSubPaths(p.p, func(sp []pathPoint) bool {
+	runSubPaths(p.p, false, func(sp []pathPoint) bool {
 		num := 0
 		prev := sp[len(sp)-1].pos
 		for _, pt := range p.p {

paths.go

@@ -362,7 +362,8 @@ func (cv *Canvas) fillPath(path *Path2D, tf mat) {
 
 	var triBuf [500][2]float64
 	tris := triBuf[:0]
-	runSubPaths(path.p, func(sp []pathPoint) bool {
+
+	runSubPaths(path.p, true, func(sp []pathPoint) bool {
 		tris = appendSubPathTriangles(tris, tf, sp)
 		return false
 	})
@@ -381,6 +382,9 @@ func appendSubPathTriangles(tris [][2]float64, mat mat, path []pathPoint) [][2]f
 	if last.flags&pathIsConvex != 0 {
 		p0, p1 := path[0].pos.mulMat(mat), path[1].pos.mulMat(mat)
 		last := len(path)
+		if path[0].pos == path[last-1].pos {
+			last--
+		}
 		for i := 2; i < last; i++ {
 			p2 := path[i].pos.mulMat(mat)
 			tris = append(tris, p0, p1, p2)
@@ -410,7 +414,7 @@ func (cv *Canvas) clip(path *Path2D, tf mat) {
 
 	var triBuf [500][2]float64
 	tris := triBuf[:0]
-	runSubPaths(path.p, func(sp []pathPoint) bool {
+	runSubPaths(path.p, true, func(sp []pathPoint) bool {
 		tris = appendSubPathTriangles(tris, tf, sp)
 		return false
 	})

triangulation.go

@@ -85,6 +85,10 @@ func polygonContainsPoint(polygon []vec, p vec) bool {
 }
 
 func triangulatePath(path []pathPoint, mat mat, target [][2]float64) [][2]float64 {
+	if path[0].pos == path[len(path)-1].pos {
+		path = path[:len(path)-1]
+	}
+
 	var buf [500]vec
 	polygon := buf[:0]
 	for _, p := range path {
@@ -345,9 +349,10 @@ func setPathLeftRightInside(net *tessNet) {
 }
 
 func selfIntersectingPathParts(p []pathPoint, partFn func(sp []pathPoint) bool) {
-	runSubPaths(p, func(sp1 []pathPoint) bool {
+	runSubPaths(p, false, func(sp1 []pathPoint) bool {
 		net := cutIntersections(sp1)
 		if net.verts == nil {
+			partFn(sp1)
 			return false
 		}