FilledCurve inside GraphicsComplex doesn't interpret the integers as points

Question

Bug introduced in V9.0 or earlier and persisting through V11.3

---

Here's an example:

Graphics[
    GraphicsComplex[
        {{-1, 0}, {0, 1}, {1, 0}}, 
        BSplineCurve[{1, 2, 3}, SplineClosed -> True]
    ],
    PlotRange -> 1.1, Axes -> True
]

works well, but when we add FilledCurve over BSplineCurve, it doesn't anymore.

FilledCurve @ BSplineCurve[{1,2,3}, SplineClosed -> True]

---

The workaround is to keep it outside GraphicsComplex:

Graphics[{
  FilledCurve @ BSplineCurve[{{-1, 0}, {0, 1}, {1, 0}}, SplineClosed -> True], 
  GraphicsComplex[{{-1, 0}, {0, 1}, {1, 0}}, Line[{1, 2, 3}]]
  },
  PlotRange -> 1.1, Axes -> True
]

But this just adds work which I would like to avoid. Is it possible?

Could that problem have been anticipated?

---

Edit: Here's a response from WRI:

It does appear as though GraphicsComplex is misbehaving with the FilledCurve option applied to BSplineCurve. I have thus filed a report with our developers so that they may look in to the issue.

In the meantime, as a workaround you could use replacement rules to get behavior similar to the GraphicsComplex functionality:

Graphics[
    FilledCurve@BSplineCurve[{1, 2, 3}, SplineClosed -> True], 
    PlotRange -> 1.1, Axes -> True
] /. Thread[Range[3] -> {{-1, 0}, {0, 1}, {1, 0}}]

Answer 1

This is fixed in M12:

Graphics[
    GraphicsComplex[
        {{-1,0},{0,1},{1,0}},
        FilledCurve@BSplineCurve[{1,2,3},SplineClosed->True]
    ],
    PlotRange->1.1,
    Axes->True
]

Answer 2

Not very clean:

v = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};

r = Normal /@ {Graphics[GraphicsComplex[v, Polygon[{1, 2, 3, 4}]]], 
               Graphics[GraphicsComplex[v, {Red, Line[{1, 2, 3, 4, 1}]}]]};

r /. {Red, Line[x__]} :> (FilledCurve@Line@x)