Tk_MeasureChars(3) Tk Tk_MeasureChars(3)
_________________________________________________________________
NAME
Tk_MeasureChars, Tk_TextWidth, Tk_DrawChars,
Tk_UnderlineChars - routines to measure and display simple
single-line strings.
SYNOPSIS
#include <tk.h>
int
Tk_MeasureChars(tkfont, string, maxChars, maxPixels, flags, lengthPtr)
int
Tk_TextWidth(tkfont, string, numChars)
void
Tk_DrawChars(display, drawable, gc, tkfont, string, numChars, x, y)
void
Tk_UnderlineChars(display, drawable, gc, tkfont, string, x, y, firstChar, lastChar)
ARGUMENTS
Tk_Font tkfont (in) Token for font in which
text is to be drawn or
measured. Must have been
returned by a previous
call to Tk_GetFont.
const char *string (in) Text to be measured or
displayed. Need not be
null terminated. Any
non-printing meta-
characters in the string
(such as tabs, newlines,
and other control
characters) will be
measured or displayed in
a platform-dependent
manner.
int maxChars (in) The maximum number of
characters to consider
when measuring string.
Must be greater than or
equal to 0.
int maxPixels (in) If maxPixels is greater
than 0, it specifies the
longest permissible line
length in pixels.
Page 1 (printed 2/26/99)
Tk_MeasureChars(3) Tk Tk_MeasureChars(3)
Characters from string
are processed only until
this many pixels have
been covered. If
maxPixels is <= 0, then
the line length is
unbounded and the flags
argument is ignored.
int flags (in) Various flag bits OR-ed
together: TK_PARTIAL_OK
means include a character
as long as any part of it
fits in the length given
by maxPixels; otherwise,
a character must fit
completely to be
considered.
TK_WHOLE_WORDS means stop
on a word boundary, if
possible. If
TK_AT_LEAST_ONE is set,
it means return at least
one character even if no
characters could fit in
the length given by
maxPixels. If
TK_AT_LEAST_ONE is set
and TK_WHOLE_WORDS is
also set, it means that
if not even one word fits
on the line, return the
first few letters of the
word that did fit; if not
even one letter of the
word fit, then the first
letter will still be
returned.
int *lengthPtr (out) Filled with the number of
pixels occupied by the
number of characters
returned as the result of
Tk_MeasureChars.
int numChars (in) The total number of
characters to measure or
draw from string. Must
be greater than or equal
to 0.
Display *display (in) Display on which to draw.
Page 2 (printed 2/26/99)
Tk_MeasureChars(3) Tk Tk_MeasureChars(3)
Drawable drawable (in) Window or pixmap in which
to draw.
GC gc (in) Graphics context for
drawing characters. The
font selected into this
GC must be the same as
the tkfont.
int x, y (in) Coordinates at which to
place the left edge of
the baseline when
displaying string.
int firstChar (in) The index of the first
character to underline in
the string. Underlining
begins at the left edge
of this character.
int lastChar (in) The index of the last
character up to which the
underline will be drawn.
The character specified
by lastChar will not
itself be underlined.
_________________________________________________________________
DESCRIPTION
These routines are for measuring and displaying simple
single-font, single-line, strings. To measure and display
single-font, multi-line, justified text, refer to the
documentation for Tk_ComputeTextLayout. There is no
programming interface in the core of Tk that supports
multi-font, multi-line text; support for that behavior must
be built on top of simpler layers.
A glyph is the displayable picture of a letter, number, or
some other symbol. Not all character codes in a given font
have a glyph. Characters such as tabs, newlines/returns,
and control characters that have no glyph are measured and
displayed by these procedures in a platform-dependent
manner; under X, they are replaced with backslashed escape
sequences, while under Windows and Macintosh hollow or solid
boxes may be substituted. Refer to the documentation for
Tk_ComputeTextLayout for a programming interface that
supports the platform-independent expansion of tab
characters into columns and newlines/returns into multi-line
text.
Tk_MeasureChars is used both to compute the length of a
Page 3 (printed 2/26/99)
Tk_MeasureChars(3) Tk Tk_MeasureChars(3)
given string and to compute how many characters from a
string fit in a given amount of space. The return value is
the number of characters from string that fit in the space
specified by maxPixels subject to the conditions described
by flags. If all characters fit, the return value will be
maxChars. *lengthPtr is filled with the computed width, in
pixels, of the portion of the string that was measured. For
example, if the return value is 5, then *lengthPtr is filled
with the distance between the left edge of string[0] and the
right edge of string[4].
Tk_TextWidth is a wrapper function that provides a simpler
interface to the Tk_MeasureChars function. The return value
is how much space in pixels the given string needs.
Tk_DrawChars draws the string at the given location in the
given drawable.
Tk_UnderlineChars underlines the given range of characters
in the given string. It doesn't draw the characters (which
are assumed to have been displayed previously by
Tk_DrawChars); it just draws the underline. This procedure
is used to underline a few characters without having to
construct an underlined font. To produce natively
underlined text, the appropriate underlined font should be
constructed and used.
KEYWORDS
font
Page 4 (printed 2/26/99)
