1. Overview

Scrollbars are used whenever some contents needs to be scrolled around. They will often be part of a ../GtkScrolledWindow, but do not need to.

The ../GtkScrollbar class has two subclasses. GtkHScrollbar is a horizontal scrollbar, and GtkVScrollbar is a vertical one. I will only discuss the horizontal scrollbar here, but vertical ones are exactly the same.

2. Style Properties

Name	Type	Default	Nick	Description	misc
fixed-slider-length	boolean	FALSE	Fixed slider size	Don't change slider size, just lock it to the minimum length
has-backward-stepper	boolean	TRUE	Backward stepper	Display the standard backward arrow button
has-forward-stepper	boolean	TRUE	Forward stepper	Display the standard forward arrow button
has-secondary-backward-stepper	boolean	FALSE	Secondary backward stepper	Display a second backward arrow button on the opposite end of the scrollbar
has-secondary-forward-stepper	boolean	FALSE	Secondary forward stepper	Display a second forward arrow button on the opposite end of the scrollbar
min-slider-length	int	21	Minimum Slider Length	Minimum length of scrollbar slider	Min: 0; Max: G_MAXINT

Also relevant are the GtkRange style properties:

Name	Type	Default	Nick	Description	misc
activate-slider	boolean	FALSE	Draw slider ACTIVE during drag	With this option set to TRUE, sliders will be drawn ACTIVE and with shadow IN while they are dragged
arrow-displacement-x	int	0	Arrow X Displacement	How far in the x direction to move the arrow when the button is depressed	Min: G_MININT; Max: G_MAXINT
arrow-displacement-y	int	0	Arrow Y Displacement	How far in the y direction to move the arrow when the button is depressed	Min: G_MININT; Max: G_MAXINT
slider-width	int	14	Slider Width	Width of scrollbar or scale thumb	Min: 0; Max: G_MAXINT
stepper-size	int	14	Stepper Size	Length of step buttons at ends	Min: 0; Max: G_MAXINT
stepper-spacing	int	0	Stepper Spacing	Spacing between step buttons and thumb	Min: 0; Max: G_MAXINT
trough-border	int	1	Trough Border	Spacing between thumb/steppers and outer trough bevel	Min: 0; Max: G_MAXINT
trough-side-details	boolean	FALSE	Trough Side Details	When TRUE, the parts of the trough on the two sides of the slider are drawn with different details
trough-under-steppers	boolean	TRUE	Trough Under Steppers	Whether to draw trough for full length of range or exclude the steppers and spacing

An exception here is probably trough-side-details which will not be interesting for scrollbars, but is very usefull for the ../GtkScale.

$/!\$ If stepper-spacing is non-zero, then trough-under-steppers is automatically disabled.

3. Geometry

3.1. trough under steppers

3.2. trough not under steppers

4. Drawing

The drawing is basically the same thing as the one from ../GtkScale, with the difference that a scrollbar has stepper buttons.

4.1. Trough

The trough is a box with a detail of "trough" and a shadow of IN. The state is ACTIVE for normal scrollbars, and INSENSITIVE if the scrollbar is insensitive. For scrollbars trough-side-details and fill level drawing can also be set. They work in exactly the same way as the one from ../GtkScale.

4.2. Slider

The slider is drawn with the slider function in GTK+ (so SLIDER in eg. the pixmap/pixbuf engine). The detail is just "slider". The state and shadow also depend on the value of the activate-slider style property. If the activate-slider style property is not set, then the slider that is dragged looks like it is in the prelight state. On the other hand, if activate-slider is set, then the slider looks differently if it is dragged.

A slider that is neither pressed, nor prelit, has a state of NORMAL and a shadow of OUT. If the mouse hovers over the slider, then the state becomes PRELIGHT, the shadow stays OUT. Then, as the slider is pressed, the state becomes ACTIVE and the shadow will be IN.

If the scrollbar is insensitive, then the slider will be drawn with a state of INSENSITIVE.

4.3. Stepper Button and Arrow

The stepper buttons have a detail of hscrollbar or vscrollbar depening on the orientation. Other than that it is drawn similar to any other button. The main thing to note is that a stepper button will be drawn insenstive if the slider is at the top or bottom. The arrows drawn with the same detail string, state and shadow, and fill_arrow is set to TRUE. It will be displaced by the number of pixels specified in the arrow-displacement-? style properties if the stepper button is pressed.

5. GTK+ API Documentation

http://library.gnome.org/devel/gtk/stable/GtkScrollbar.html