Sliders
A slider allows the user to quickly select a value from a fixed, ordered range, or to increase or decrease the current value. The control looks like the type of slider that you might find on an audio mixing desk or a hi-fi's graphic equalizer. In gtk, you implement a slider using the GtkHScale or GtkVScale controls, for horizontal or vertical sliders respectively.
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Use a slider when:
- adjusting the value relative to its current value is more important than choosing an absolute value. 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.
- it is useful for the user to control the rate of change of the value in real time. For example, to monitor the effects of a color change in a live preview window as they drag the RGB sliders.
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Label the slider with a text label above it or to its left, using sentence capitalization. Provide an access key in the label that allows the user to give focus directly to the slider.
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Mark significant values along the length of the slider with text or tick marks. For example the left, right and center points on an audio balance control in Figure 6-7.
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For large ranges of integers (more than about 20), and for ranges of floating point numbers, consider providing a text box or spin box that is linked to the slider's value. This allows the user to quickly set or fine-tune the setting more easily than they could with the slider control alone.
Figure 6-8 Slider controls with linked spin boxes