[kde-guidelines] Styleguide: Slider

[Heiko Tietze]

HIG>Constrained input 
* Use a [[Projects/Usability/HIG/Slider|Slider]] for arbitrary changes within 
a defined range.

http://techbase.kde.org/Projects/Usability/HIG/Slider

Purpose
A slider is a widget with which a user may set a value by moving an indicator, 
usually in a horizontal fashion. The user may also click on a point on the 
slider to change the setting. It is different from a scrollbar in that it is 
typically used to adjust a value without changing the format of the display or 
the other information on the screen. A slider is used to set defined, 
contiguous values or a range of discrete values. It is a good choice when 
values have a relative quantity, not a numeric value. Usually, changes made on 
the slider are shown immediately. That instant feedback supports input that is 
not necessarily precise. Compared with spin controls a slider provides faster 
changes within a larger range but with lower accuracy. Sliders are almost 
solely operable by mouse.

Guidelines
* Use a slider when adjusting... "For example, a volume control: the average 
user will usually think about turning the volume up or down to make a sound 
louder or quieter, rather than setting the peak output to a specific decibel 
value." 
-> Example part removed because it's too verbose

* Use a slider when it is useful ... "For example, to monitor the effects of a 
color change in a live preview window as they drag the RGB sliders" 
-> Example part removed because it's too verbose

"* If the value is open-ended on one or both ends, consider using a 
[[../Spin_Box|Spin Box]] instead." 
-> Removed completely because spin boxes have limits as well.

* Mark significant values... "For example the left, right and center points on 
an audio balance control in Figure 6.7, “A simple slider control”." 
-> Example part removed 

"* For cases where the values are constrained at both ends and there large 
ranges of integers (more than about 20) or floating-point values that require 
precise control, consider providing both a [[../Slider_and_Spin_Box|Slider and 
Spin Box]]. This allows the user to quickly set or fine-tune the setting more 
easily than they could with the slider control alone." 
-> Removed completely because it is redundant

Added
* Don't change the size of the slider indicator from the default size.
* Give immediate feedback while user makes a selection. 
* Size the control so that a user can easily set the desired value. 
And for discussion because non-linear scales are sometimes recommended for 
large ranges:
* Do not use a non-linear scale, e.g. logarithmic.