Tk::Font - Create and inspect fonts.
$widget->Font(option?,
arg, arg, ...?)
$font->Option?(arg,
arg, ...)?
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.
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.
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.
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.
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
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.