If you position the value on the "side" of the trough (e.g., on the top or bottom of a horizontal scale widget), then it will follow the slider up and down the trough.
All the preceding functions are defined in <gtk/gtkscale.h>. The header files for all GTK widgets are automatically included when you include <gtk/gtk.h>. But you should look over the header files of all widgets that interest you,
8.3 Common Range Functions
The Range widget class is fairly complicated internally, but, like all the "base class" widgets, most of its complexity is only interesting if you want to hack on it. Also, almost all of the functions and signals it defines are only really used in writing derived widgets. There are, however, a few useful functions that are defined in <gtk/gtkrange.h> and will work on all range widgets.
Setting the Update Policy
The "update policy" of a range widget defines at what points during user interaction it will change the value field of its Adjustment and emit the "value_changed" signal on this Adjustment. The update policies, defined in <gtk/gtkenums.h> as type enum GtkUpdateType, are:
GTK_UPDATE_POLICY_CONTINUOUS - This is the default. The "value_changed" signal is emitted continuously, i.e., whenever the slider is moved by even the tiniest amount.
GTK_UPDATE_POLICY_DISCONTINUOUS - The "value_changed" signal is only emitted once the slider has stopped moving and the user has released the mouse button.
GTK_UPDATE_POLICY_DELAYED - The "value_changed" signal is emitted when the user releases the mouse button, or if the slider stops moving for a short period of time.
The update policy of a range widget can be set by casting it using the GTK_RANGE (Widget) macro and passing it to this function:
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Getting and Setting Adjustments
Getting and setting the adjustment for a range widget "on the fly" is done, predictably, with:
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gtk_range_get_adjustment() returns a pointer to the adjustment to which range is connected.
gtk_range_set_adjustment() does absolutely nothing if you pass it the adjustment that range is already using, regardless of whether you changed any of its fields or not. If you pass it a new Adjustment, it will unreference the old one if it exists (possibly destroying it), connect the appropriate signals to the new one, and call the private function gtk_range_adjustment_changed(), which will (or at least, is supposed to...) recalculate the size and/or position of the slider and redraw if necessary. As mentioned in the section on adjustments, if you wish to reuse the same Adjustment, when you modify its values directly, you should emit the "changed" signal on it, like this:
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8.4 Key and Mouse bindings
All of the GTK range widgets react to mouse clicks in more or less the same way. Clicking button-1 in the trough will cause its adjustment's page_increment to be added or subtracted from its value, and the slider to be moved accordingly. Clicking mouse button-2 in the trough will jump the slider to the point at which the button was clicked. Clicking any button on a scrollbar's arrows will cause its adjustment's value to change step_increment at a time.
It may take a little while to get used to, but by default, scrollbars as well as scale widgets can take the keyboard focus in GTK. If you think your users will find this too confusing, you can always disable this by unsetting the GTK_CAN_FOCUS flag on the scrollbar, like this:
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The key bindings (which are, of course, only active when the widget has focus) are slightly different between horizontal and vertical range widgets, for obvious reasons. They are also not quite the same for scale widgets as they are for scrollbars, for somewhat less obvious reasons (possibly to avoid confusion between the keys for horizontal and vertical scrollbars in scrolled windows, where both operate on the same area).
Vertical Range Widgets
All vertical range widgets can be operated with the up and down arrow keys, as well as with the Page Up and Page Down keys. The arrows move the slider up and down by step_increment, while Page Up and Page Down move it by page_increment.
