tk_measurechars(3)

NAME

Tk_MeasureChars, Tk_TextWidth, Tk_DrawChars, Tk_Under
lineChars - routines to measure and display simple singleline strings.

SYNOPSIS

#include <tk.h>
int
Tk_MeasureChars(tkfont,   string,   numBytes,   maxPixels,
flags, lengthPtr)
int
Tk_TextWidth(tkfont, string, numBytes)
void
Tk_DrawChars(display,   drawable,   gc,   tkfont,  string,
numBytes, x, y)
void
Tk_UnderlineChars(display, drawable, gc,  tkfont,  string,
x, y, firstByte, lastByte)

ARGUMENTS

Tk_Font tkfont (in) Token for font in which

text is to be drawn or
measured. Must have
been returned by a pre
vious call to Tk_Get
Font.

const char *string (in) Text to be measured or

displayed. Need not be
null terminated. Any
non-printing meta-char
acters in the string
(such as tabs, new
lines, and other con
trol characters) will
be measured or dis
played in a platformdependent manner.

int num_
Bytes (in)

The maximum number of
bytes to consider when
measuring or drawing
string. Must be greater than or equal
to 0.

int maxPixels (in) If maxPixels is >= 0,

it specifies the
longest permissible
line length in pixels.
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 charac
ter as long as any part
of it fits in the
length given by maxPix_ els; otherwise, a char
acter must fit com
pletely to be consid
ered. 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 charac
ters returned as the
result of Tk_Mea
sureChars.

Display *display (in) Display on which to

draw.

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 dis
playing string.

int first_
Byte (in)

The index of the first
byte of the first char
acter to underline in
the string. Underlin
ing begins at the left
edge of this character.

int last_
Byte (in)

The index of the first
byte of the last char
acter up to which the
underline will be
drawn. The character
specified by lastByte 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 doc
umentation for Tk_ComputeTextLayout. There is no program ming 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. Note that the interfaces
described here are byte-oriented not character-oriented,
so index values coming from Tcl scripts need to be con
verted to byte offsets using the Tcl_UtfAtIndex and related routines.

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, new
lines/returns, and control characters that have no glyph
are measured and displayed by these procedures in a plat
form-dependent manner; under X, they are replaced with
backslashed escape sequences, while under Windows and Mac
intosh hollow or solid boxes may be substituted. Refer to
the documentation for Tk_ComputeTextLayout for a program ming interface that supports the platform-independent
expansion of tab characters into columns and new
lines/returns into multi-line text.

Tk_MeasureChars is used both to compute the length of a 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 bytes 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
numBytes. *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 proce dure 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

Tk 8.1 Tk_MeasureChars(3)