Tk::Font(3pm) - Man pages

Font(3pm) User Contributed Perl Documentation Font(3pm)

NAME
Tk::Font - Create and inspect fonts.

SYNOPSIS
$widget->Font(option?, arg, arg, ...?)

$font->Option?(arg, arg, ...)?

DESCRIPTION
The Font method provides several facilities for dealing with fonts, such
as defining named fonts and inspecting the actual attributes of a font.
The command has several different forms, determined by the first
argument. The following forms are currently supported:

$font->actual(-option?)
$widget->fontActual(font?, -option?)
Returns information about the actual attributes that are obtained
when font is used on $font's display; the actual attributes obtained
may differ from the attributes requested due to platform-dependant
limitations, such as the availability of font families and
pointsizes. font is a font description; see "FONT DESCRIPTION"
below. If option is specified, returns the value of that attribute;
if it is omitted, the return value is a list of all the attributes
and their values. See "FONT OPTIONS" below for a list of the
possible attributes.

$font->configure(-option??=>value, -option=>value, ...?)
Query or modify the desired attributes for $font. If no -option is
specified, returns a list describing all the options and their
values for fontname. If a single -option is specified with no
value, then returns the current value of that attribute. If one or
more option-value pairs are specified, then the method modifies the
given named font to have the given values; in this case, all widgets
using that font will redisplay themselves using the new attributes
for the font. See "FONT OPTIONS" below for a list of the possible
attributes.

Note: the above behaviour differs in detail to configure on widgets,
images etc.

$font = $widget->Font(-option=>value, ...>?)
$font = $widget->fontCreate(?fontname??, -option=>value, ...>?)
Creates a new font object and returns a reference to it. fontname
specifies the name for the font; if it is omitted, then Tk generates
a new name of the form fontx, where x is an integer. There may be
any number of option-value pairs, which provide the desired
attributes for the new named font. See "FONT OPTIONS" below for a
list of the possible attributes.

Note: the created font is not shared between widgets of different
MainWindows.

$font->delete
$widget->fontDelete(fontname?, fontname, ...?)
Delete the specified named fonts. If there are widgets using the
named font, the named font won't actually be deleted until all the
instances are released. Those widgets will continue to display
using the last known values for the named font. If a deleted named
font is subsequently recreated with another call to fontCreate, the
widgets will use the new named font and redisplay themselves using
the new attributes of that font.

$widget->fontFamilies
The return value is a list of the case-insensitive names of all font
families that exist on $widget's display.

$font->measure(text)
$widget->fontMeasure(font, text)
Measures the amount of space the string text would use in the given
font when displayed in $widget. font is a font description; see
"FONT DESCRIPTION" below. The return value is the total width in
pixels of text, not including the extra pixels used by highly
exagerrated characters such as cursive ``f''. If the string
contains newlines or tabs, those characters are not expanded or
treated specially when measuring the string.

$font->metrics(-option?)
$widget->fontMetrics(font?, -option?)
Returns information about the metrics (the font-specific data), for
font when it is used on $widget's display. font is a font
description; see "FONT DESCRIPTION" below. If option is specified,
returns the value of that metric; if it is omitted, the return value
is a list of all the metrics and their values. See "FONT METRICS"
below for a list of the possible metrics.

$widget->fontNames
The return value is a list of all font objects that are currently
defined for $widget's MainWindow.

FONT DESCRIPTION
The following formats are accepted as a font description anywhere font
is specified as an argument above; these same forms are also permitted
when specifying the -font option for widgets.

[1] fontname
The name of a named font, created using the fontCreate method. When
a widget uses a named font, it is guaranteed that this will never
cause an error, as long as the named font exists, no matter what
potentially invalid or meaningless set of attributes the named font
has. If the named font cannot be displayed with exactly the
specified attributes, some other close font will be substituted
automatically.

[1a] $font
A font object created using the Font method. This is essentially the
same as using a named font. The object is a reference to the name,
and carries additional information e.g. which MainWindow it relates
to in an manner peculiar to perl/Tk.

[2] systemfont
The platform-specific name of a font, interpreted by the graphics
server. This also includes, under X, an XLFD (see [4]) for which a
single ``*'' character was used to elide more than one field in the
middle of the name. See "PLATFORM-SPECIFIC ISSUES" for a list of
the system fonts.

[3] [family,?size,??style,??style ...?]
A properly formed list whose first element is the desired font
family and whose optional second element is the desired size. The
interpretation of the size attribute follows the same rules
described for -size in "FONT OPTIONS" below. Any additional
optional arguments following the size are font styles. Possible
values for the style arguments are as follows:

normal bold roman italic
underline overstrike

[4] X-font names (XLFD)
A Unix-centric font name of the form
-foundry-family-weight-slant-setwidth-addstyle-pixel-point-resx-resy-spacing-width-charset-encoding.
The ``*'' character may be used to skip individual fields that the
user does not care about. There must be exactly one ``*'' for each
field skipped, except that a ``*'' at the end of the XLFD skips any
remaining fields; the shortest valid XLFD is simply ``*'',
signifying all fields as defaults. Any fields that were skipped are
given default values. For compatibility, an XLFD always chooses a
font of the specified pixel size (not point size); although this
interpretation is not strictly correct, all existing applications
using XLFDs assumed that one ``point'' was in fact one pixel and
would display incorrectly (generally larger) if the correct size
font were actually used.

[5] option value ?option value ...?
A properly formed list of option-value pairs that specify the
desired attributes of the font, in the same format used when
defining a named font; see "FONT OPTIONS" below.

When font description font is used, the system attempts to parse the
description according to each of the above five rules, in the order
specified. Cases [1] and [2] must match the name of an existing named
font or of a system font. Cases [3], [4], and [5] are accepted on all
platforms and the closest available font will be used. In some
situations it may not be possible to find any close font (e.g., the font
family was a garbage value); in that case, some system-dependant default
font is chosen. If the font description does not match any of the above
patterns, an error is generated.

FONT METRICS
The following options are used by the metrics/fontMetrics method to
query font-specific data determined when the font was created. These
properties are for the whole font itself and not for individual
characters drawn in that font. In the following definitions, the
``baseline'' of a font is the horizontal line where the bottom of most
letters line up; certain letters, such as lower-case ``g'' stick below
the baseline.

-ascent
The amount in pixels that the tallest letter sticks up above the
baseline of the font, plus any extra blank space added by the
designer of the font. ($font->ascent is provided for
compatibility.)

-descent
The largest amount in pixels that any letter sticks down below the
baseline of the font, plus any extra blank space added by the
designer of the font. ($font->descent is provided for
compatibility.)

-linespace
Returns how far apart vertically in pixels two lines of text using
the same font should be placed so that none of the characters in one
line overlap any of the characters in the other line. This is
generally the sum of the ascent above the baseline line plus the
descent below the baseline.

-fixed
Returns a boolean flag that is ``1'' if this is a fixed-width font,
where each normal character is the the same width as all the other
characters, or is ``0'' if this is a proportionally-spaced font,
where individual characters have different widths. The widths of
control characters, tab characters, and other non-printing
characters are not included when calculating this value.

FONT OPTIONS
The following options are supported on all platforms, and are used when
constructing a named font or when specifying a font using style [5] as
above:

-family => name
The case-insensitive font family name. Tk guarantees to support the
font families named Courier (a monospaced ``typewriter'' font),
Times (a serifed ``newspaper'' font), and Helvetica (a sans-serif
``European'' font). The most closely matching native font family
will automatically be substituted when one of the above font
families is used. The name may also be the name of a native,
platform-specific font family; in that case it will work as desired
on one platform but may not display correctly on other platforms.
If the family is unspecified or unrecognized, a platform-specific
default font will be chosen.

-size => size
The desired size of the font. If the size argument is a positive
number, it is interpreted as a size in points. If size is a
negative number, its absolute value is interpreted as a size in
pixels. If a font cannot be displayed at the specified size, a
nearby size will be chosen. If size is unspecified or zero, a
platform-dependent default size will be chosen.

The original Tcl/Tk authors believe sizes should normally be
specified in points so the application will remain the same ruler
size on the screen, even when changing screen resolutions or moving
scripts across platforms. While this is an admirable goal it does
not work as well in practice as they hoped. The mapping between
points and pixels is set when the application starts, based on
alleged properties of the installed monitor, but it can be
overridden by calling the scaling command. However this can be
problematic when system has no way of telling if (say) an 11" or 22"
monitor is attached, also if it can tell then some monitor sizes may
result in poorer quality scaled fonts being used rather than a
"tuned" bitmap font. In addition specifying pixels is useful in
certain circumstances such as when a piece of text must line up with
respect to a fixed-size bitmap.

At present the Tcl/Tk scheme is used unchanged, with "point" size
being returned by actual (as an integer), and used internally.
Suggestions for work-rounds to undesirable behaviour welcome.

-weight => weight
The nominal thickness of the characters in the font. The value
normal specifies a normal weight font, while bold specifies a bold
font. The closest available weight to the one specified will be
chosen. The default weight is normal.

-slant => slant
The amount the characters in the font are slanted away from the
vertical. Valid values for slant are roman and italic. A roman
font is the normal, upright appearance of a font, while an italic
font is one that is tilted some number of degrees from upright. The
closest available slant to the one specified will be chosen. The
default slant is roman.

-underline => boolean
The value is a boolean flag that specifies whether characters in
this font should be underlined. The default value for underline is
false.

-overstrike => boolean
The value is a boolean flag that specifies whether a horizontal line
should be drawn through the middle of characters in this font. The
default value for overstrike is false.

PLATFORM-SPECIFIC ISSUES
The following named system fonts are supported:

X Windows:
All valid X font names, including those listed by xlsfonts(1), are
available.

MS Windows:
system ansi device
systemfixed ansifixed oemfixed

Macintosh:
system application

COMPATIBILITY WITH PREVIOUS VERSIONS
In prior versions of perl/Tk the $widget->Font method was a perl wrapper
on the original "[4] X-font names (XLFD)" style as described above
(which was the only form supported by versions of core tk prior to
version tk8.0). This module is provided in its original form (it has
just been renamed) via:

use Tk::X11Font;
I<$widget>-E<gt>B<X11Font>(...)

However the methods of the old scheme have been mimiced as closely as
possible with the new scheme. It is intended that code should work
without modification, except for the case of using :

@names = $font->Name;

i.e. the Name method in an array/list context. This now returns one
element on all platforms (as it did on Win32), while previously on X
systems it returned a list of fonts that matched an under-specified
pattern.

Briefly the methods supported for compatibility are as follows:

$newfont = $font->Clone(-option=>value, ...>?)
Returns a new font object $newfont related to the original $font by
changing the values of the specified -options.

$font->Family - maps to -family
$font->Weight - maps to -weight
$font->Slant - maps to -slant
$font->Pixel and Point - map to -size

New code should use $font->configure to achieve same effect as last four
items above.

Foundry, Swidth, Adstyle, Xres, Yres, Space, Avgwidth, Registry,
Encoding
Are all ignored if set, and return '*' if queried.

$font->Name
Returns the name of a named font, or a string representation of an
unnamed font. Using $font in a scalar context does the same. Note
this is distinctly different from behaviour of X11Font's Name in a
list context.

$font->Pattern
Returns a XLFD string for the font based on actual values, and some
heuristics to map Tk's forms to the "standard" X conventions.