= class Gtk::Adjustment
The Gtk::Adjustment object represents a value which has an associated lower and upper bound, together with step and page increments, and a page size. It is used within several Ruby/GTK widgets, including Gtk::SpinButton, Gtk::Viewport, and Gtk::Range (which is a base class for Gtk:HScrollbar, Gtk::VScrollbar, Gtk::HScale, and Gtk::VScale). 

The Gtk::Adjustment object does not update the value itself. Instead it is left up to the owner of the Gtk::Adjustment to control the value. 

The owner of the Gtk::Adjustment typically calls the Gtk::Adjustment#value_changed and Gtk::Adjustment#changed functions after changing the value and its bounds. This results in the emission of the "value_changed" or "changed" signal respectively. 

== Object Hierarchy
* Object
  * GLib::Instantiatable
    * GLib::Object
      * Gtk::Object
        * Gtk::Adjustment


== Class Methods
--- Gtk::Adjustment.new(value, lower, upper, step_inc, page_inc, page_size)
    Creates a new Gtk::Adjustment. All argument types are Float. 
    * value: the initial value. 
    * lower: the minimum value. 
    * upper: the maximum value. 
    * step_increment: the increment to use to make minor changes to the value. In a Gtk::Scrollbar this increment is used when the mouse is clicked on the arrows at the top and bottom of the scrollbar, to scroll by a small amount.  
    * page_increment: the increment to use to make major changes to the value. In a Gtk::Scrollbar this increment is used when the mouse is clicked in the trough, to scroll by a large amount.  
    * page_size: the page size. In a Gtk::Scrollbar this is the size of the area which is currently visible.  

== Instance Methods
--- value
    Gets the current value of the adjustment. See Gtk::Adjustment#value=.
    * Returns: The current value of the adjustment

--- value=(value)
    Sets the Gtk::Adjustment value. 
    * value : the new value
    * Returns: value

--- set_value
    Same as value=.
    * value : the new value
    * Returns: self

--- step_increment(step_increment)
    Gets the step_increment value. See Gtk::Adjustment#step_increment=.
    * Returns: step_increment

--- step_increment=(step_increment)
    Sets the increment to use to make minor changes to the value. 
    * step_increment : the new step_increment value.
    * Returns: step_increment

--- set_step_increment(step_increment)
    Same as step_increment=.
    * step_increment : the new step_increment value.
    * Returns: self

--- clamp_page
    Updates the Gtk::Adjustment value to ensure that the range between lower and upper is in the current page (i.e. between value and value + page_size). If the range is larger than the page size, then only the start of it will be in the current page. A "changed" signal will be emitted if the value is changed. 
    * lower: the lower value.  
    * upper: the upper value.  
    * Returns: self

--- lower
    Gets the minimum value of the adjustment. See Gtk::Adjustment#clamp_page.
    * Returns: The minimum value of the adjustment

--- upper
    Gets the maximum value of the adjustment. See Gtk::Adjustment#clamp_page.
    * Returns: The maximum value of the adjustment

--- page_increment
    Gets the increment to use to make major changes to the value of the adjustment. See Gtk::Adjustment.new.
    * Returns: The increment to use to make major changes to the value of the adjustment

--- page_increment=(page_increment)
    Sets the increment to use to make major changes to the value of the adjustment. 
    * page_increment : the new page_increment value.
    * Returns: page_increment

--- set_page_increment(page_increment)
    Same as page_increment=.
    * page_increment : the new page_increment value.
    * Returns: self

--- page_size
    Gets the page size value of the adjustment. See Gtk::Adjustment.new.
    * Returns: The page size value of the adjustment

--- page_size=(page_size)
    Sets the page size value of the adjustment. 
    * page_size : the new page_size value.
    * Returns: page_size

--- set_page_size(page_size)
    Same as page_size=.
    * page_size : the new page_size value.
    * Returns: self

--- changed
    Emits a "changed" signal from the Gtk::Adjustment. This is typically called by the owner of the Gtk::Adjustment after it has changed any of the Gtk::Adjustment fields other than the value. 
--- value_changed
    Emits a "value_changed" signal from the Gtk::Adjustment. This is typically called by the owner of the Gtk::Adjustment after it has changed the Gtk::Adjustment value field. 
    
== Signals
--- changed: self
     * self: Gtk::Adjustment

--- value-changed: self
     * self: Gtk::Adjustment

- ((<Masao>))