pack(3)
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 oneat-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 par
cel (except leave external padding
as specified by -padx). - y Stretch the slave vertically to
- fill the entire height of its par
cel (except leave external padding
as specified by -pady). - both Stretch the slave both horizon
- tally 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->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 configu
ration state of the slave given by $slave in the same
option-value form that might be specified to packCon figure. The first two elements of the list are
``-in=>$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 "GEOME
TRY PROPAGATION" below). If boolean has a false
boolean value then propagation is disabled for $mas_
ter. 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 cur
rently 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 mas
ter 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 unal
located. 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 cav
ity 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 par cel 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 nor
mally 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 dimen
sions. 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 par
ent (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