op/clip: fix Path open state

If a Move/MoveTo did not move the pen, the Path
was still set as open.

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

op/clip/clip.go

@@ -154,6 +154,9 @@ func (p *Path) Move(delta f32.Point) {
 
 // MoveTo moves the pen to the specified absolute coordinate.
 func (p *Path) MoveTo(to f32.Point) {
+	if p.pen == to {
+		return
+	}
 	p.open = p.open || p.pen != p.start
 	p.end()
 	p.pen = to

op/clip/clip_test.go

@@ -4,6 +4,7 @@ package clip_test
 
 import (
 	"image/color"
+	"math"
 	"testing"
 
 	"gioui.org/f32"
@@ -13,7 +14,8 @@ import (
 	"gioui.org/op/paint"
 )
 
-func TestOpenPathOutlinePanic(t *testing.T) {
+func TestPathOutline(t *testing.T) {
+	t.Run("unclosed path", func(t *testing.T) {
 		defer func() {
 			if err := recover(); err == nil {
 				t.Error("Outline of an open path didn't panic")
@@ -23,6 +25,23 @@ func TestOpenPathOutlinePanic(t *testing.T) {
 		p.Begin(new(op.Ops))
 		p.Line(f32.Pt(10, 10))
 		clip.Outline{Path: p.End()}.Op()
+	})
+	t.Run("closed path", func(t *testing.T) {
+		defer func() {
+			if err := recover(); err != nil {
+				t.Error("Outline of a closed path did panic")
+			}
+		}()
+		var p clip.Path
+		p.Begin(new(op.Ops))
+		p.MoveTo(f32.Pt(300, 200))
+		p.LineTo(f32.Pt(150, 200))
+		p.MoveTo(f32.Pt(150, 200))
+		p.ArcTo(f32.Pt(300, 200), f32.Pt(300, 200), 3*math.Pi/4)
+		p.LineTo(f32.Pt(300, 200))
+		p.Close()
+		clip.Outline{Path: p.End()}.Op()
+	})
 }
 
 func TestPathBegin(t *testing.T) {