Reference TFlatVertexBuffer

  TFlatVertexBuffer = class(TDrawingBuffer<TFlatVertex>)
  protected
    function CountAttributes: Integer; override;
    procedure BindAttributes; override;
  public
    { Add a vertex, returning the buffer so calls can be chained }
    function Add(const V: TVec2): TFlatVertexBuffer; overload;
    function Add(X, Y: Float): TFlatVertexBuffer; overload;
  end;