Fix issue with line resize

Fixes #2208

canvas/line.go

@@ -45,9 +45,12 @@ func (l *Line) Position() fyne.Position {
 
 // Move the line object to a new position, relative to its parent / canvas
 func (l *Line) Move(pos fyne.Position) {
-	size := l.Size()
-	l.Position1 = pos
-	l.Position2 = fyne.NewPos(l.Position1.X+size.Width, l.Position1.Y+size.Height)
+	oldPos := l.Position()
+	deltaX := pos.X - oldPos.X
+	deltaY := pos.Y - oldPos.Y
+
+	l.Position1 = l.Position1.Add(fyne.NewPos(deltaX, deltaY))
+	l.Position2 = l.Position2.Add(fyne.NewPos(deltaX, deltaY))
 }
 
 // MinSize for a Line simply returns Size{1, 1} as there is no

canvas/line_test.go

@@ -18,6 +18,25 @@ func TestLine_MinSize(t *testing.T) {
 	assert.True(t, min.Height > 0)
 }
 
+func TestLine_Move(t *testing.T) {
+	line := canvas.NewLine(color.Black)
+
+	line.Resize(fyne.NewSize(10, 10))
+	assert.Equal(t, fyne.NewPos(0, 0), line.Position1)
+	assert.Equal(t, fyne.NewPos(10, 10), line.Position2)
+
+	line.Move(fyne.NewPos(5, 5))
+	assert.Equal(t, fyne.NewPos(5, 5), line.Position1)
+	assert.Equal(t, fyne.NewPos(15, 15), line.Position2)
+
+	// rotate
+	line.Position1 = fyne.NewPos(0, 10)
+	line.Position2 = fyne.NewPos(10, 0)
+	line.Move(fyne.NewPos(10, 10))
+	assert.Equal(t, fyne.NewPos(10, 20), line.Position1)
+	assert.Equal(t, fyne.NewPos(20, 10), line.Position2)
+}
+
 func TestLine_Resize(t *testing.T) {
 	line := canvas.NewLine(color.Black)