stk/Doc/Manual/font.n

'\"
'\" Copyright (c) 1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
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'\" SCCS: @(#) font.n 1.9 97/05/20 20:32:34
'\" 
.so STk-man.macros
.TH font n 4.0 Tk "Tk Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
font \- Create and inspect fonts.
.SH SYNOPSIS
(\fBfont\fI option \fR?\fIarg arg ...\fR?)
.BE
.SH DESCRIPTION
.PP
The \fBfont\fR procedure provides several facilities for dealing with
fonts, such as defining named fonts and inspecting the actual attributes of
a font.  The procedure has several different forms, determined by the
first argument.  The following forms are currently supported:
.TP
(\fBfont 'actual \fIfont\fR ?\fB\:displayof \fIwindow\fR? ?\fIoption\fR?)
.
Returns information about the the actual attributes that are obtained when
\fIfont\fR is used on \fIwindow\fR'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.
\fIfont\fR is a font description; see FONT DESCRIPTIONS below.  If the
\fIwindow\fR argument is omitted, it defaults to the main window.  If
\fIoption\fR 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.
.TP 
(\fBfont 'configure \fIfontname\fR ?\fIoption\fR? ?\fIvalue option value ...\fR?)
.
Query or modify the desired attributes for the named font called
\fIfontname\fR.  If no \fIoption\fR is specified, returns a list describing
all the options and their values for \fIfontname\fR.  If a single \fIoption\fR 
is specified with no \fIvalue\fR, then returns the current value of that
attribute.  If one or more \fIoption\fR\-\fIvalue\fR pairs are specified,
then the procedure 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.
.TP
(\fBfont 'create\fR ?\fIfontname\fR? ?\fIoption value ...\fR?)
.
Creates a new named font and returns its name.  \fIfontname\fR specifies the
name for the font; if it is omitted, then Tk generates a new name of the
form "\fBfont\fIx\fR", where \fIx\fR is an integer.  There may be any number
of \fIoption\fR\-\fIvalue\fR pairs, which provide the desired attributes for
the new named font.  See FONT OPTIONS below for a list of the possible
attributes.
.TP
(\fBfont 'delete\fR \fIfontname\fR ?\fIfontname ...\fR?)
.
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 \fBfont create\fR, the widgets will use the new named font
and redisplay themselves using the new attributes of that font.
.TP
(\fBfont 'families\fR)
.TP
(\fBfont 'families\fR \fB\:displayof \fIwindow\fR?)
.
The return value is a list of the case-insensitive names of all font families 
that exist on \fIwindow\fR's display.  If the \fIwindow\fR argument is
omitted, it defaults to the main window.
.TP
(\fBfont 'measure \fIfont\fR ?\fB\:displayof \fIwindow\fR? \fItext\fR)
.
Measures the amount of space the string \fItext\fR would use in the given
\fIfont\fR when displayed in \fIwindow\fR.  \fIfont\fR is a font description;
see FONT DESCRIPTIONS below.  If the \fIwindow\fR argument is omitted, it
defaults to the main window.  The return value is the total width in pixels
of \fItext\fR, 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.
.TP
(\fBfont 'metrics \fIfont\fR ?\fB\:displayof \fIwindow\fR? ?\fIoption\fR?)
.
Returns information about the metrics (the font-specific data), for
\fIfont\fR when it is used on \fIwindow\fR's display.  \fIfont\fR is a font
description; see FONT DESCRIPTIONS below.  If the \fIwindow\fR argument is
omitted, it defaults to the main window.  If \fIoption\fR 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.
.TP
(\fBfont 'names\fR)
The return value is a list of all the named fonts that are currently defined.
.SH "FONT DESCRIPTION"
.PP
The following formats are accepted as a font description anywhere
\fIfont\fR is specified as an argument above; these same forms are also
permitted when specifying the \fB:font\fR option for widgets.
.TP
[1] \fIfontname\fR 
.
The name of a named font, created using the \fBfont create\fR procedure.  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.
.TP
[2] \fIsystemfont\fR
.
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 ``\fB*\fR''
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.
.VS 8.0 br
.TP
[3] \fIfamily \fR?\fIsize\fR? ?\fIstyle\fR? ?\fIstyle ...\fR?
.
A properly formed list whose first element is the desired font
\fIfamily\fR and whose optional second element is the desired \fIsize\fR.
The interpretation of the \fIsize\fR attribute follows the same rules
described for \fB:size\fR in FONT OPTIONS below.  Any additional optional
arguments following the \fIsize\fR are font \fIstyle\fRs.  Possible values
for the \fIstyle\fR arguments are as follows:
.RS
.DS
.ta 3c 6c 9c
\fBnormal	bold	roman	italic	
underline	overstrike\fR
.DE
.RE
.TP 
[4] X-font names (XLFD)
.
A Unix-centric font name of the form
\fI-foundry-family-weight-slant-setwidth-addstyle-pixel-point-resx-resy-spacing-width-charset-encoding\fR.
The ``\fB*\fR'' character may be used to skip individual fields that the
user does not care about.  There must be exactly one ``\fB*\fR'' for each
field skipped, except that a ``\fB*\fR'' at the end of the XLFD skips any
remaining fields; the shortest valid XLFD is simply ``\fB*\fR'', 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.
.VE
.TP
[5] \fIoption value \fR?\fIoption value ...\fR?
.
A properly formed list of \fIoption\fR\-\fIvalue\fR pairs that specify
the desired attributes of the font, in the same format used when defining
a named font; see FONT OPTIONS below.
.LP
When font description \fIfont\fR 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.  
.SH "FONT METRICS"
.
The following options are used by the \fBfont metrics\fR procedure 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.
.TP
\fB:ascent        \0\fR
.
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.
.TP
\fB:descent       \0\fR 
.
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.
.TP
\fB:linespace\fR
.
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.
.TP
\fB:fixed          \0\fR
.
Returns a boolean flag that is ``\fB#t\fR'' if this is a fixed-width font,
where each normal character is the the same width as all the other
characters, or is ``\fB#f\fR'' 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.
.SH "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:
.TP
\fB:family \fIname\fR 
.
The case-insensitive font family name.  Tk guarantees to support the font
families named \fBCourier\fR (a monospaced ``typewriter'' font), \fBTimes\fR
(a serifed ``newspaper'' font), and \fBHelvetica\fR (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 \fIname\fR 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.
.TP
\fB:size \fIsize\fR
.
The desired size of the font.  If the \fIsize\fR argument is a positive
number, it is interpreted as a size in points.  If \fIsize\fR 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 \fIsize\fR is unspecified or zero, a platform-dependent default
size will be chosen.  
.RS
.PP
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.  However, specifying pixels is useful in
certain circumstances such as when a piece of text must line up with respect
to a fixed-size bitmap.  The mapping between points and pixels is set when
the application starts, based on properties of the installed monitor, but it
can be overridden by calling  \fB(tk-state 'scaling)\fR.
.RE
.TP
\fB:weight \fIweight\fR 
.
The nominal thickness of the characters in the font.  The value
\fBnormal\fR specifies a normal weight font, while \fBbold\fR specifies a
bold font.  The closest available weight to the one specified will
be chosen.  The default weight is \fBnormal\fR.
.TP
\fB:slant \fIslant\fR
The amount the characters in the font are slanted away from the
vertical.  Valid values for slant are \fBroman\fR and \fBitalic\fR.
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 \fBroman\fR.
.TP
\fB:underline \fIboolean\fR
The value is a boolean flag that specifies whether characters in this
font should be underlined.  The default value for underline is \fB#f\fR.
.TP
\fB:overstrike \fIboolean\fR 
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 \fB#f\fR.

.SH "PLATFORM-SPECIFIC ISSUES"
.LP
The following named system fonts are supported:
.RS
.TP 
X Windows:
All valid X font names, including those listed by xlsfonts(1), are available.
.TP
MS Windows:
.DS
\fBsystem	ansi	device
systemfixed	ansifixed	oemfixed\fR
.DE
.TP
Macintosh:
.DS
\fBsystem	application\fR
.DE
.RE