Tk_MeasureChars(3) Tk Library Procedures Tk_MeasureChars(3)

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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, numBytes, maxPixels, flags, lengthPtr)

int
Tk_TextWidth(tkfont, string, numBytes)

Tk_DrawChars(display, drawable, gc, tkfont, string, numBytes, x, y)

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 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 numBytes (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
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.

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
displaying string.

int firstByte (in) The index of the first byte of the
first character to underline in
the string. Underlining begins at
the left edge of this character.

int lastByte (in) The index of the first byte of the
last character up to which the
underline will be drawn. The
character specified by lastByte
will not itself be underlined.
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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. Note that the interfaces described here
are byte-oriented not character-oriented, so index values coming from
Tcl scripts need to be converted 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, 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 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 does not 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.

SEE ALSO

font(n), FontId(3)

KEYWORDS

font, measurement

Tk 8.1 Tk_MeasureChars(3)