func (f *Field) PieceDroppable(piece *Piece, x, y int, angle Angle) bool {
	return !piece.collides(f, x, y+1, angle)
}
func (f *Field) PieceDroppable(piece *Piece, x, y int, angle Angle) bool {
	return !piece.collides(f, x, y+1, angle)
}
// PieceDroppable returns a boolean value indicating whether
// the piece at (x, y) with the given angle can drop.