Chapter 12. Adjustments

Table of Contents

gtkmm has various widgets that can be visually adjusted using the mouse or the keyboard, such as the Range widgets (described in the Range Widgets section). There are also a few widgets that display some adjustable part of a larger area, such as the Viewport widget. These widgets have Gtk::Adjustment objects that express this common part of their API.

So that applications can react to changes, for instance when a user moves a scrollbar, Gtk::Adjustment has a changed signal. You can then use the get_changed() method to discover the new value.

Creating an Adjustment

The Gtk::Adjustment constructor is as follows:

Gtk::Adjustment(float value,
                float lower,
                float upper,
                float step_increment = 1,
                float page_increment = 10,
                float page_size = 0);

The value argument is the initial value of the adjustment, usually corresponding to the topmost or leftmost position of an adjustable widget. The lower and upper arguments specifies the possible range of values which the adjustment can hold. The step_increment argument specifies the smaller of the two increments by which the user can change the value, while the page_increment is the larger one. The page_size argument usually corresponds somehow to the visible area of a panning widget. The upper argument is used to represent the bottom most or right most coordinate in a panning widget's child. TODO: Investigate the upper argument properly. There was some unclear stuff about it not always being the upper value.


Examples		Using Adjustments the Easy Way