code: func (gt *GLTriangles) Position(i int) pixel.Vec {
  	px := gt.data[i*gt.vs.Stride()+0]
  	py := gt.data[i*gt.vs.Stride()+1]
  	return pixel.V(float64(px), float64(py))
  }
docs: // Position returns the Position property of the i-th vertex.