thumb-length

Arguments: scroll-bar

Returns the value of the thumb-length property of scroll-bar controls (vertical-scroll-bar and horizontal-scroll-bar). Its value is either a positive integer that indicates how large the "thumb" (also called the elevator or scroll-box) of the scroll-bar should be, or else nil to use a default size. The thumb will be drawn such that the length of the thumb compared to the length of the rest of the interior scroll-bar length is proportional to the thumb-length property compared to the size (scroll-max - scroll-min) of the scroll-range property.

If a scroll-bar control is being used to scroll a portion of some drawing into a scrollable area (as window scrollbars do), then typically an application would set the thumb-length to the size of the visible area and scroll-range to the size of the portion of the picture that does not fit within the visible area. Otherwise the thumb-length may not be relevant, and the default size (where thumb-length is nil) may be best.

In releases prior to 6.0, this property was called visible-portion. That symbol still names this function (and the :visible-portion initarg is still accepted), but use of visible-portion is deprecated. Further, the meaning has changed somewhat.

In releases prior to 6.0, the range of a standalone scroll-bar control included the thumb-length (then called visible-portion), which made it similar to the whole page of a scrollable window rather than the scrolling range (which is the page minus the visible portion of the page). This was an inconsistent usage of the Common Graphics scroll-range concept. It also meant, for example, if the range of a standalone scroll-bar control was 0 to 100 and the thumb-length was 20, then the possible values of the scrollbar actually ranged from 0 to 80 rather than the alleged range of 0 to 100. Starting in release 6.0, the range no longer includes the thumb-length.

It is not possible to disable a scroll-bar dialog-item by setting its thumb-length to be greater than or equal to the range. You can disable a scroll-bar control by setting the range with the min value equal to the max value, such as (0 0). (Also, as with other controls, scroll-bars may be disabled by setting its available property to nil.)

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This page was not revised from the 10.0 page.
Created 2019.8.20.