added sorting of font contours for correct triangulation

earcut.go

@@ -799,3 +799,109 @@ func (ec *earcut) removeNode(p *node) {
 		p.nextZ.prevZ = p.prevZ
 	}
 }
+
+// sortFontContours takes the contours of a font glyph
+// and checks whether each contour is the outside or a
+// hole, and returns an array that is sorted so that
+// it contains an index of an outer contour followed by
+// any number of indices of hole contours followed by
+// a terminating -1
+func sortFontContours(contours [][]backendbase.Vec) []int {
+	type cut struct {
+		idx   int
+		count int
+	}
+	type info struct {
+		cuts     []cut
+		cutTotal int
+		outer    bool
+	}
+
+	cutBuf := make([]cut, len(contours)*len(contours))
+	cinf := make([]info, len(contours))
+	for i := range contours {
+		cinf[i].cuts = cutBuf[i*len(contours) : i*len(contours)]
+	}
+
+	// go through each contour, pick one point on it, and
+	// project that point to the right. count the number of
+	// other contours that it cuts
+	for i, p1 := range contours {
+		pt := p1[0]
+		for j, p2 := range contours {
+			if i == j {
+				continue
+			}
+
+			for k := range p2 {
+				a, b := p2[k], p2[(k+1)%len(p2)]
+				if a == b {
+					continue
+				}
+
+				minY := math.Min(a[1], b[1])
+				maxY := math.Max(a[1], b[1])
+
+				if pt[1] <= minY || pt[1] > maxY {
+					continue
+				}
+
+				r := (pt[1] - a[1]) / (b[1] - a[1])
+				x := (b[0]-a[0])*r + a[0]
+				if x <= pt[0] {
+					continue
+				}
+
+				found := false
+				for l := range cinf[i].cuts {
+					if cinf[i].cuts[l].idx == j {
+						cinf[i].cuts[l].count++
+						found = true
+						break
+					}
+				}
+				if !found {
+					cinf[i].cuts = append(cinf[i].cuts, cut{idx: j, count: 1})
+				}
+				cinf[i].cutTotal++
+			}
+		}
+	}
+
+	// any contour with an even number of cuts is outer,
+	// odd number of cuts means it is a hole
+	for i := range cinf {
+		cinf[i].outer = cinf[i].cutTotal%2 == 0
+	}
+
+	// go through them again, pick any outer contour, then
+	// find any hole where the first outer contour it cuts
+	// an odd number of times is the picked contour and add
+	// it to the list of its holes
+	result := make([]int, 0, len(contours)*2)
+	for i := range cinf {
+		if !cinf[i].outer {
+			continue
+		}
+		result = append(result, i)
+
+		for j := range cinf {
+			if cinf[j].outer {
+				continue
+			}
+			for _, cut := range cinf[j].cuts {
+				if cut.count%2 == 0 {
+					continue
+				}
+				if cut.idx == i {
+					result = append(result, j)
+					break
+				}
+			}
+		}
+
+		result = append(result, -1)
+	}
+
+	return result
+}

text.go

@@ -596,7 +596,7 @@ func (cv *Canvas) runeTris(rn rune) []backendbase.Vec {
 	var gb truetype.GlyphBuf
 	gb.Load(cv.state.font.font, baseFontSize, idx, font.HintingFull)
 
-	polyWithHoles := make([][]backendbase.Vec, 0, len(gb.Ends))
+	contours := make([][]backendbase.Vec, 0, len(gb.Ends))
 
 	from := 0
 	for _, to := range gb.Ends {
@@ -608,7 +608,7 @@ func (cv *Canvas) runeTris(rn rune) []backendbase.Vec {
 			others = ps[1:]
 		} else {
 			last := ps[len(ps)-1]
-			if ps[len(ps)-1].Flags&0x01 != 0 {
+			if last.Flags&0x01 != 0 {
 				start = last
 				others = ps[:len(ps)-1]
 			} else {
@@ -652,30 +652,63 @@ func (cv *Canvas) runeTris(rn rune) []backendbase.Vec {
 		}
 		path.ClosePath()
 
-		poly := make([]backendbase.Vec, len(path.p))
+		contour := make([]backendbase.Vec, len(path.p))
 		for i, pt := range path.p {
-			poly[i] = pt.pos
+			contour[i] = pt.pos
 		}
 
-		polyWithHoles = append(polyWithHoles, poly)
+		contours = append(contours, contour)
 
 		from = to
 	}
 
+	idxs := sortFontContours(contours)
+	sortedContours := make([][]backendbase.Vec, 0, len(idxs))
+	trisList := make([][]backendbase.Vec, 0, len(contours))
+
+	for i := 0; i < len(idxs); {
+		var j int
+		for j = i; j < len(idxs); j++ {
+			if idxs[j] == -1 {
+				break
+			}
+		}
+
+		sortedContours = sortedContours[:j-i]
+		for k, idx := range idxs[i:j] {
+			sortedContours[k] = contours[idx]
+		}
+
 		var ec earcut
-	ec.run(polyWithHoles)
+		ec.run(sortedContours)
 
 		tris := make([]backendbase.Vec, len(ec.indices))
 		for i, idx := range ec.indices {
 			pidx := 0
-		poly := polyWithHoles[pidx]
+			poly := sortedContours[pidx]
 			for idx >= len(poly) {
 				idx -= len(poly)
 				pidx++
-			poly = polyWithHoles[pidx]
+				poly = sortedContours[pidx]
 			}
 			tris[i] = poly[idx]
 		}
+		trisList = append(trisList, tris)
+
+		i = j + 1
+	}
+
+	count := 0
+	for _, tris := range trisList {
+		count += len(tris)
+	}
+
+	allTris := make([]backendbase.Vec, count)
+	pos := 0
+	for _, tris := range trisList {
+		copy(allTris[pos:], tris)
+		pos += len(tris)
+	}
 
 	cache, ok := cv.fontTriCache[cv.state.font]
 	if !ok {
@@ -683,9 +716,9 @@ func (cv *Canvas) runeTris(rn rune) []backendbase.Vec {
 		cv.fontTriCache[cv.state.font] = cache
 	}
 	cache.lastUsed = time.Now()
-	cache.cache[idx] = tris
+	cache.cache[idx] = allTris
 
-	return tris
+	return allTris
 }
 
 // TextMetrics is the result of a MeasureText call