GravityView
fGravityView = new GravityView(view->Bounds(), this);
class GravityView;
GravityView* fGravityView;
GravityView::GravityView(BRect frame, Gravity* parent)
GravityView::~GravityView()
GravityView::AttachedToWindow()
GravityView::DirectDraw()
class GravityView : public BGLView {
GravityView(BRect frame, Gravity* parent);
~GravityView();