slider.md
In rswipl: Embed 'SWI'-'Prolog'

class slider {#class-slider}

A slider is a graphical representation of a numeric value in a predefined range. The value can be changed by dragging the slider. Sliders are commonly used to view/edit numeric values that should not be exact (it is difficult to drag to an exact value). Examples are the speed of something or a percentage(done).

A slider selects or visualises an numeric value in the range (<-low, <-high). Its current value is (as with all dialog_item objects) accessible through <->selection. The exact value is normally shown in textual form as well. This may be controlled by <->show_value. ->show_label determines whether or not the label visible.

If either <-low or <-high is a real object, the slider will assume it operates on floating point numbers. If both <-low and <-high is integer, the slider will assume integer values. So, to specify a slider from 0 to 10 in floating point, use:

?- new(S, slider(value, 0,0, 10.0, 5.0)).

When a slider is operated by the user (by dragging the value), <-message may be send either on termination or at each drag-event. This is controlled by <->drag. When message is executed, the arguments are:

| @receiver | The slider              |
| @arg1     | The current <-selection |
| @arg2     | The event object.       |

Bugs: Sliders should be able to handle ranges of floating-point numbers too.

@see class scroll_bar @see class dialog_item @see class text_item

slider-default: int|real|function The default selection or function to get it. Used by ->restore.
slider<->drag: bool When @on, <-message will be activated on each drag-event received by the slider. Otherwise, <-message will only be sent when the mouse-button is released.

Defaults: @off (only send at mouse-up).
slider<-format: [name] Format specification used to represent the textual values. The specification is as for the C printf() call (see also string->format). The default format for floating point values is %f and for integers %d. The following defines a slider in 0.01 steps from 0.0 .. 1.0:
```
?- new(S, slider(value, 0.0, 1.0, 0.5)),
   send(S, format, '%.2f').
```
slider<-high: int|real Together with <-low this variable describes the (including) range.

@see slider-selection @see slider-low
slider<-label_font: font* Font used to print the <-label if <-show_label equals @on.

@see slider-show_label
slider<-low: int|real Lowest value for <->selection. See ->high.

@see slider-selection @see slider-high
slider<-selection: int|real Current value. An integer for which <-low <= <-selection <= <-high.

@see slider-high @see slider-low
slider<-show_label: bool When @on, the <-label of the slider is printed at the left-side in <-label_font.

Defaults: @on

@see slider-show_value @see slider-label_font
slider<-show_value: bool When @on, the current value is printed in textual format too. It will be printed in <-value_font.

Defaults: @on

@see slider-value_font @see slider-show_label
slider<-value_font: font @see slider-show_value
slider-width: int Length of the bar-part of the slider in pixels.

Defaults: 200 pixels.

slider->compute Computes the layout and sets <-area and <-reference using the various attributes.
slider->default: value=int|real|function Sets the -default value and the ->selection.
slider->event: event A slider is operated by the left pointer-button. It will execute it's <-message when the user releases the button (<-drag: @off) or anytime the user moves the pointer with the button held down (<-drag: @on).

First tries dialog_item <-event.
slider->initialise: name, low=int|real, high=int|real, value=int|real|function, message=[code]* Create a slider object from its <-label, <-low, <-high and ->default.
slider->modified: bool Inherits description from: slider<-modified

slider<-default: -> int|real If -default holds a function, execute it and return the result. Otherwise return the plain value of -default. Used by ->restore.
slider<-modified: -> bool A slider is considered modified if the currently displayed value (<-selection) is not equal to the <-displayed_value.

->modified: @off sets <-displayed_value to <-selection.