vector: Bug fix: Wrong rendering when there are some same points

Updates #845

vector/internal/math/triangulate.go

@@ -44,8 +44,21 @@ func Triangulate(pts []Point) []uint16 {
 
 	var currentIndices []uint16
 
-	// Remove duplicated points
+	// Split pts into the two point groups if there are the same points.
 	for i := range pts {
+		for j := 0; j < i; j++ {
+			if pts[i] == pts[j] {
+				is0 := Triangulate(pts[j:i])
+				for idx := range is0 {
+					is0[idx] += uint16(j)
+				}
+				is1 := Triangulate(append(pts[i:], pts[:j]...))
+				for idx := range is1 {
+					is1[idx] = uint16((int(is1[idx]) + i) % len(pts))
+				}
+				return append(is0, is1...)
+			}
+		}
 		currentIndices = append(currentIndices, uint16(i))
 	}
 
@@ -61,12 +74,6 @@ func Triangulate(pts []Point) []uint16 {
 		// Determine the direction of the polygon from the upper-left point.
 		var upperLeft int
 		for i := range currentIndices {
-			next := (i + 1) % len(currentIndices)
-			if pts[currentIndices[i]] == pts[currentIndices[next]] {
-				idxToRemove = next
-				break
-			}
-
 			i0, i1, i2 := adjacentIndices(currentIndices, i)
 			pt0 := pts[i0]
 			pt1 := pts[i1]
@@ -112,10 +119,6 @@ func Triangulate(pts []Point) []uint16 {
 				if l := len(currentIndices); j == (i+l-1)%l || j == i || j == (i+1)%l {
 					continue
 				}
-				jj := currentIndices[j]
-				if pts[i0] == pts[jj] || pts[i1] == pts[jj] || pts[i2] == pts[jj] {
-					continue
-				}
 				if InTriangle(pts[currentIndices[j]], pt0, pt1, pt2) {
 					// If the triangle includes another point, the triangle is not an ear.
 					continue index

vector/internal/math/triangulate_test.go

@@ -213,7 +213,7 @@ func TestTriangulate(t *testing.T) {
 				{3, 1},
 				{2, 0},
 			},
-			Out: []uint16{8, 0, 1, 1, 2, 4, 1, 4, 5, 8, 1, 5, 8, 5, 7},
+			Out: []uint16{6, 7, 8, 6, 8, 0, 4, 0, 1, 4, 1, 3},
 		},
 		{
 			In: []Point{
@@ -248,14 +248,14 @@ func TestTriangulate(t *testing.T) {
 		{
 			// Butterfly
 			In: []Point{
-				{0, 0},
 				{0, 2},
 				{1, 1},
 				{2, 2},
 				{2, 0},
 				{1, 1},
+				{0, 0},
 			},
-			Out: []uint16{5, 0, 1, 5, 3, 4},
+			Out: []uint16{3, 1, 2, 0, 4, 5},
 		},
 		{
 			In: []Point{
@@ -268,7 +268,30 @@ func TestTriangulate(t *testing.T) {
 				{6, 0},
 				{6, 3},
 			},
-			Out: []uint16{7, 0, 1, 7, 1, 2, 7, 4, 5, 7, 5, 6},
+			Out: []uint16{6, 3, 4, 6, 4, 5, 2, 7, 0, 2, 0, 1},
+		},
+		{
+			In: []Point{
+				{0, 4},
+				{0, 6},
+				{2, 6},
+				{2, 5},
+				{3, 5},
+				{3, 4},
+				{4, 4},
+				{4, 2},
+				{6, 2},
+				{6, 1},
+				{5, 1},
+				{5, 0},
+				{4, 0},
+				{4, 2},
+				{2, 2},
+				{2, 3},
+				{1, 3},
+				{1, 4},
+			},
+			Out: []uint16{7, 8, 9, 7, 9, 10, 12, 7, 10, 12, 10, 11, 6, 13, 14, 6, 14, 15, 6, 15, 16, 17, 0, 1, 17, 1, 2, 16, 17, 2, 16, 2, 3, 16, 3, 4, 16, 4, 5, 6, 16, 5},
 		},
 	}
 	for _, tc := range tests {