pack(3pm) User Contributed Perl Documentation pack(3pm)
NAME
Tk::pack - Geometry manager that packs around edges of cavity
SYNOPSIS
$widget->pack?(args)?
$widget->packOption?(args)?
DESCRIPTION
The pack method is used to communicate with the packer, a geometry
manager that arranges the children of a parent by packing them in order
around the edges of the parent.
In this perl port of Tk it is normal to pack widgets one-at-a-time using
the widget object to be packed to invoke a method call. This is a
slight distortion of underlying Tk interface (which can handle lists of
windows to one pack method call) but has proven effective in practice.
The pack method can have any of several forms, depending on Option:
$slave->pack?(options)?
The options consist of pairs of arguments that specify how to manage
the slave. See "THE PACKER ALGORITHM" below for details on how the
options are used by the packer. The following options are
supported:
-after => $other
$other must be another window. Use its master as the master
for the slave, and insert the slave just after $other in the
packing order.
-anchor => anchor
Anchor must be a valid anchor position such as n or sw; it
specifies where to position each slave in its parcel.
Defaults to center.
-before => $other
$other must be another window. Use its master as the master
for the slave, and insert the slave just before $other in
the packing order.
-expand => boolean
Specifies whether the slave should be expanded to consume
extra space in their master. Boolean may have any proper
boolean value, such as 1 or no. Defaults to 0.
-fill => style
If a slave's parcel is larger than its requested dimensions,
this option may be used to stretch the slave. Style must
have one of the following values:
none Give the slave its requested dimensions plus any
internal padding requested with -ipadx or
-ipady. This is the default.
x Stretch the slave horizontally to fill the
entire width of its parcel (except leave
external padding as specified by -padx).
y Stretch the slave vertically to fill the entire
height of its parcel (except leave external
padding as specified by -pady).
both Stretch the slave both horizontally and
vertically.
-in => $master
Insert the slave(s) at the end of the packing order for the
master window given by $master.
-ipadx => amount
Amount specifies how much horizontal internal padding to
leave on each side of the slave(s). Amount must be a valid
screen distance, such as 2 or .5c. It defaults to 0.
-ipady => amount
Amount specifies how much vertical internal padding to leave
on each side of the slave(s). Amount defaults to 0.
-padx => amount
Amount specifies how much horizontal external padding to
leave on each side of the slave(s). Amount defaults to 0.
-pady => amount
Amount specifies how much vertical external padding to leave
on each side of the slave(s). Amount defaults to 0.
-side => side
Specifies which side of the master the slave(s) will be
packed against. Must be left, right, top, or bottom.
Defaults to top.
If no -in, -after or -before option is specified then slave will be
inserted at the end of the packing list for its parent unless it is
already managed by the packer (in which case it will be left where it
is). If one of these options is specified then slave will be inserted
at the specified point. If the slave are already managed by the
geometry manager then any unspecified options for them retain their
previous values rather than receiving default values.
$slave->packConfigure?(options)?
Same as pack.
$slave->packForget
Removes slave from the packing order for its master and unmaps its
window. The slave will no longer be managed by the packer.
$slave->packInfo
Returns a list whose elements are the current configuration state of
the slave given by $slave in the same option-value form that might
be specified to packConfigure. The first two elements of the list
are ``-in=>$master'' where $master is the slave's master.
$master->packPropagate?(boolean)?
If boolean has a true boolean value such as 1 or on then propagation
is enabled for $master, (see "GEOMETRY PROPAGATION" below). If
boolean has a false boolean value then propagation is disabled for
$master. In either of these cases an empty string is returned. If
boolean is omitted then the method returns 0 or 1 to indicate
whether propagation is currently enabled for $master. Propagation
is enabled by default.
$master->packSlaves
Returns a list of all of the slaves in the packing order for
$master. The order of the slaves in the list is the same as their
order in the packing order. If $master has no slaves then an empty
list/string is returned in array/scalar context, respectively
THE PACKER ALGORITHM
For each master the packer maintains an ordered list of slaves called
the packing list. The -in, -after, and -before configuration options
are used to specify the master for each slave and the slave's position
in the packing list. If none of these options is given for a slave then
the slave is added to the end of the packing list for its parent.
The packer arranges the slaves for a master by scanning the packing list
in order. At the time it processes each slave, a rectangular area
within the master is still unallocated. This area is called the cavity;
for the first slave it is the entire area of the master.
For each slave the packer carries out the following steps:
[1] The packer allocates a rectangular parcel for the slave along the
side of the cavity given by the slave's -side option. If the side
is top or bottom then the width of the parcel is the width of the
cavity and its height is the requested height of the slave plus the
-ipady and -pady options. For the left or right side the height of
the parcel is the height of the cavity and the width is the
requested width of the slave plus the -ipadx and -padx options. The
parcel may be enlarged further because of the -expand option (see
"EXPANSION" below)
[2] The packer chooses the dimensions of the slave. The width will
normally be the slave's requested width plus twice its -ipadx option
and the height will normally be the slave's requested height plus
twice its -ipady option. However, if the -fill option is x or both
then the width of the slave is expanded to fill the width of the
parcel, minus twice the -padx option. If the -fill option is y or
both then the height of the slave is expanded to fill the width of
the parcel, minus twice the -pady option.
[3] The packer positions the slave over its parcel. If the slave is
smaller than the parcel then the -anchor option determines where in
the parcel the slave will be placed. If -padx or -pady is non-zero,
then the given amount of external padding will always be left
between the slave and the edges of the parcel.
Once a given slave has been packed, the area of its parcel is
subtracted from the cavity, leaving a smaller rectangular cavity for
the next slave. If a slave doesn't use all of its parcel, the
unused space in the parcel will not be used by subsequent slaves.
If the cavity should become too small to meet the needs of a slave
then the slave will be given whatever space is left in the cavity.
If the cavity shrinks to zero size, then all remaining slaves on the
packing list will be unmapped from the screen until the master
window becomes large enough to hold them again.
EXPANSION
If a master window is so large that there will be extra space left over
after all of its slaves have been packed, then the extra space is
distributed uniformly among all of the slaves for which the -expand
option is set. Extra horizontal space is distributed among the
expandable slaves whose -side is left or right, and extra vertical space
is distributed among the expandable slaves whose -side is top or bottom.
GEOMETRY PROPAGATION
The packer normally computes how large a master must be to just exactly
meet the needs of its slaves, and it sets the requested width and height
of the master to these dimensions. This causes geometry information to
propagate up through a window hierarchy to a top-level window so that
the entire sub-tree sizes itself to fit the needs of the leaf windows.
However, the packPropagate method may be used to turn off propagation
for one or more masters. If propagation is disabled then the packer
will not set the requested width and height of the packer. This may be
useful if, for example, you wish for a master window to have a fixed
size that you specify.
RESTRICTIONS ON MASTER WINDOWS
The master for each slave must either be the slave's parent (the
default) or a descendant of the slave's parent. This restriction is
necessary to guarantee that the slave can be placed over any part of its
master that is visible without danger of the slave being clipped by its
parent.
PACKING ORDER
If the master for a slave is not its parent then you must make sure that
the slave is higher in the stacking order than the master. Otherwise
the master will obscure the slave and it will appear as if the slave
hasn't been packed correctly. The easiest way to make sure the slave is
higher than the master is to create the master window first: the most
recently created window will be highest in the stacking order. Or, you
can use the raise and lower methods to change the stacking order of
either the master or the slave.
SEE ALSO
Tk::form Tk::grid Tk::place
KEYWORDS
geometry manager, location, packer, parcel, propagation, size
perl v5.40.1 2025-04-13 pack(3pm)
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