func drawPolygon(ctxt draw2d.GraphicContext, g *geos.Geometry, fillColor color.Color, strokeColor color.Color, width float64, scale func(x, y float64) (float64, float64)) { ctxt.SetFillColor(fillColor) ctxt.SetStrokeColor(strokeColor) ctxt.SetLineWidth(width) // exterior ring ring := geos.Must(g.ExteriorRing()) cs, err := ring.coordSeq() if err != nil { log.Fatal(err) } lineCoordSeq(ctxt, cs, scale) ctxt.FillStroke() // interior rings... }