Tk_MeasureChars(3)
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 charac-
ters) 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 pix-
els have been covered.
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Tk_MeasureChars(3) Tk Library Procedures Tk_MeasureChars(3)
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 com-
pletely 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 max-
Pixels. 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
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Tk_MeasureChars(3) Tk Library Procedures Tk_MeasureChars(3)
place the left edge of
the baseline when
displaying string.
int firstByte (in) The index of the first
byte of the first charac-
ter 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 charac-
ter 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 docu-
mentation 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 sup-
ports 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 speci-
fied by maxPixels subject to the conditions described by
flags. If all characters fit, the return value will be num-
Bytes. *lengthPtr is filled with the computed width, in
pixels, of the portion of the string that was measured. For
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Tk_MeasureChars(3) Tk Library Procedures Tk_MeasureChars(3)
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 con-
struct 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 Last change: 8.1 4
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