scrollbar(3)

NAME

Tk::Scrollbar - Create and manipulate Scrollbar widgets

SYNOPSIS

$scrollbar = $parent->Scrollbar(?options?);

STANDARD OPTIONS

-activebackground -highlightbackground -ori ent -takefocus -background -highlight color -relief -troughcolor -borderwidth -high lightthickness -repeatdelay -cursor -jump -repeatin terval

See Tk::options for details of the standard options.

WIDGET-SPECIFIC OPTIONS

Name: activeRelief
Class: ActiveRelief
Switch: -activerelief: Specifies the relief to use when displaying the ele
ment that is active, if any. Elements other than the
active element are always displayed with a raised
relief.
Name: command
Class: Command
Switch: -command: Specifies a callback to invoke to change the view in
the widget associated with the scrollbar. When a user
requests a view change by manipulating the scrollbar,
the callback is invoked. The callback is passed addi
tional arguments as described later. This option
almost always has a value such as [xview => $widget] or [yview => $widget], consisting of the a widget object and either xview (if the scrollbar is for hori
zontal scrolling) or yview (for vertical scrolling).
All scrollable widgets have xview and yview methods that take exactly the additional arguments appended by
the scrollbar as described in "SCROLLING COMMANDS"
below.
Name: elementBorderWidth
Class: BorderWidth
Switch: -elementborderwidth: Specifies the width of borders drawn around the inter
nal elements of the scrollbar (the two arrows and the
slider). The value may have any of the forms accept
able to Tk_GetPixels. If this value is less than zero, the value of the borderWidth option is used in its place.
Name: width
Class: Width
Switch: -width: Specifies the desired narrow dimension of the scroll
bar window, not including 3-D border, if any. For
vertical scrollbars this will be the width and for
horizontal scrollbars this will be the height. The
value may have any of the forms acceptable to Tk_Get
Pixels.

DESCRIPTION

The Scrollbar method creates a new window (given by the $widget argument) and makes it into a scrollbar widget.
Additional options, described above, may be specified on
the command line or in the option database to configure
aspects of the scrollbar such as its colors, orientation,
and relief. The scrollbar command returns its $widget argument. At the time this command is invoked, there must
not exist a window named $widget, but $widget's parent
must exist.

A scrollbar is a widget that displays two arrows, one at
each end of the scrollbar, and a slider in the middle por
tion of the scrollbar. It provides information about what
is visible in an associated window that displays an docu ment of some sort (such as a file being edited or a draw
ing). The position and size of the slider indicate which
portion of the document is visible in the associated win
dow. For example, if the slider in a vertical scrollbar
covers the top third of the area between the two arrows,
it means that the associated window displays the top third
of its document.

Scrollbars can be used to adjust the view in the associ
ated window by clicking or dragging with the mouse. See
"BINDINGS" below for details.

ELEMENTS

A scrollbar displays five elements, which are referred to
in the methods for the scrollbar:

arrow1: The top or left arrow in the scrollbar.
trough1: The region between the slider and arrow1.
slider: The rectangle that indicates what is visible in the
associated widget.
trough2: The region between the slider and arrow2.
arrow2: The bottom or right arrow in the scrollbar.

WIDGET METHODS

The Scrollbar method creates a widget object. This object supports the configure and cget methods described in Tk::options which can be used to enquire and modify the
options described above. The widget also inherits all the
methods provided by the generic Tk::Widget class.

The following additional methods are available for scroll
bar widgets:

$scrollbar->activate(?element?): Marks the element indicated by element as active,
which causes it to be displayed as specified by the
activeBackground and activeRelief options. The only element values understood by this command are arrow1,
slider, or arrow2. If any other value is specified then no element of the scrollbar will be active. If
element is not specified, the command returns the name of the element that is currently active, or an empty
string if no element is active.
$scrollbar->delta(deltaX, deltaY): Returns a real number indicating the fractional change
in the scrollbar setting that corresponds to a given
change in slider position. For example, if the
scrollbar is horizontal, the result indicates how much
the scrollbar setting must change to move the slider
deltaX pixels to the right (deltaY is ignored in this case). If the scrollbar is vertical, the result indi
cates how much the scrollbar setting must change to
move the slider deltaY pixels down. The arguments and the result may be zero or negative.
$scrollbar->fraction(x, y): Returns a real number between 0 and 1 indicating where
the point given by x and y lies in the trough area of
the scrollbar. The value 0 corresponds to the top or
left of the trough, the value 1 corresponds to the
bottom or right, 0.5 corresponds to the middle, and so
on. X and y must be pixel coordinates relative to the
scrollbar widget. If x and y refer to a point outside
the trough, the closest point in the trough is used.
$scrollbar->get: Returns the scrollbar settings in the form of a list
whose elements are the arguments to the most recent
set method.
$scrollbar->identify(x, y): Returns the name of the element under the point given
by x and y (such as arrow1), or an empty string if the point does not lie in any element of the scrollbar. X
and y must be pixel coordinates relative to the
scrollbar widget.
$scrollbar->set(first, last): This command is invoked by the scrollbar's associated
widget to tell the scrollbar about the current view in
the widget. The command takes two arguments, each of
which is a real fraction between 0 and 1. The frac
tions describe the range of the document that is visi
ble in the associated widget. For example, if first
is 0.2 and last is 0.4, it means that the first part
of the document visible in the window is 20% of the
way through the document, and the last visible part is
40% of the way through.

SCROLLING COMMANDS

When the user interacts with the scrollbar, for example by
dragging the slider, the scrollbar notifies the associated
widget that it must change its view. The scrollbar makes
the notification by evaluating a callback specified as the
scrollbar's -command option. The callback may take sev eral forms. In each case, the intial arguments passed are
those specified in the -command callback itself, which usually has a form like [yview => $widget]. (Which will invoke $widget->yview(...) where the ... part is as below. See Tk::callbacks for details.) The callback is passed
additional arguments as follows:

moveto,fraction: Fraction is a real number between 0 and 1. The widget should adjust its view so that the point given by
fraction appears at the beginning of the widget. If fraction is 0 it refers to the beginning of the docu ment. 1.0 refers to the end of the document, 0.333
refers to a point one-third of the way through the
document, and so on.
scroll,number,units: The widget should adjust its view by number units.
The units are defined in whatever way makes sense for
the widget, such as characters or lines in a text wid
get. Number is either 1, which means one unit should
scroll off the top or left of the window, or -1, which
means that one unit should scroll off the bottom or
right of the window.
scroll,number,page: The widget should adjust its view by number pages. It is up to the widget to define the meaning of a page;
typically it is slightly less than what fits in the
window, so that there is a slight overlap between the
old and new views. Number is either 1, which means
the next page should become visible, or -1, which
means that the previous page should become visible.

OLD COMMAND SYNTAX

In versions of Tk before 4.0, the set and get widget com
mands used a different form. This form is still supported
for backward compatibility, but it is deprecated. In the
old command syntax, the set method has the following form:

$scrollbar->set(totalUnits, windowUnits, firstUnit, lastU_ nit): In this form the arguments are all integers. TotalU_
nits gives the total size of the object being dis
played in the associated widget. The meaning of one
unit depends on the associated widget; for example,
in a text editor widget units might correspond to
lines of text. WindowUnits indicates the total number of units that can fit in the associated window at one
time. FirstUnit and lastUnit give the indices of the first and last units currently visible in the associ
ated window (zero corresponds to the first unit of the
object).
Under the old syntax the get method returns a list of four
integers, consisting of the totalUnits, windowUnits, firstUnit, and lastUnit values from the last set method.
The callbacks generated by scrollbars also have a differ ent form when the old syntax is being used, the callback is passed a single argument:
unit: Unit is an integer that indicates what should appear
at the top or left of the associated widget's window.
It has the same meaning as the firstUnit and lastUnit arguments to the set method.
The most recent set method determines whether or not to
use the old syntax. If it is given two real arguments
then the new syntax will be used in the future, and if it
is given four integer arguments then the old syntax will
be used.

BINDINGS

Tk automatically creates class bindings for scrollbars
that give them the following default behavior. If the
behavior is different for vertical and horizontal scroll
bars, the horizontal behavior is described in parentheses.

[1] Pressing button 1 over arrow1 causes the view in the: associated widget to shift up (left) by one unit so
that the document appears to move down (right) one
unit. If the button is held down, the action
auto-repeats.
[2] Pressing button 1 over trough1 causes the view in the: associated widget to shift up (left) by one screenful
so that the document appears to move down (right) one
screenful. If the button is held down, the action
auto-repeats.
[3] Pressing button 1 over the slider and dragging causes: the view to drag with the slider. If the jump option
is true, then the view doesn't drag along with the
slider; it changes only when the mouse button is
released.
[4] Pressing button 1 over trough2 causes the view in the: associated widget to shift down (right) by one screen
ful so that the document appears to move up (left) one
screenful. If the button is held down, the action
auto-repeats.
[5] Pressing button 1 over arrow2 causes the view in the: associated widget to shift down (right) by one unit so
that the document appears to move up (left) one unit.
If the button is held down, the action auto-repeats.
[6] If button 2 is pressed over the trough or the slider,: it sets the view to correspond to the mouse position;
dragging the mouse with button 2 down causes the view
to drag with the mouse. If button 2 is pressed over
one of the arrows, it causes the same behavior as
pressing button 1.
[7] If button 1 is pressed with the Control key down, then: if the mouse is over arrow1 or trough1 the view changes to the very top (left) of the document; if
the mouse is over arrow2 or trough2 the view changes to the very bottom (right) of the document; if the
mouse is anywhere else then the button press has no
effect.
[8] In vertical scrollbars the Up and Down keys have the: same behavior as mouse clicks over arrow1 and arrow2, respectively. In horizontal scrollbars these keys
have no effect.
[9] In vertical scrollbars Control-Up and Control-Down: have the same behavior as mouse clicks over trough1
and trough2, respectively. In horizontal scrollbars these keys have no effect.
[10]: In horizontal scrollbars the Up and Down keys have the
same behavior as mouse clicks over arrow1 and arrow2, respectively. In vertical scrollbars these keys have
no effect.
[11]: In horizontal scrollbars Control-Up and Control-Down
have the same behavior as mouse clicks over trough1
and trough2, respectively. In vertical scrollbars
these keys have no effect.
[12]: The Prior and Next keys have the same behavior as
mouse clicks over trough1 and trough2, respectively.
[13]: The Home key adjusts the view to the top (left edge)
of the document.
[14]: The End key adjusts the view to the bottom (right
edge) of the document.

KEYWORDS

scrollbar, widget

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