Tk_MeasureChars - man pages section 3: Extended Library Functions, Volume 1

Language:

Tk_MeasureChars (3tk)

Name

Tk_MeasureChars - tines 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)

Description

Tk_MeasureChars(3tk) Tk Library Procedures Tk_MeasureChars(3tk)

______________________________________________________________________________

NAME
Tk_MeasureChars, Tk_TextWidth, Tk_DrawChars, Tk_UnderlineChars - rou-
tines 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 con-
sider 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 max-
Pixels 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 char-
acter 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 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 let-
ters 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_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 charac-
ters. 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 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 char-
acter 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 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. Charac-
ters 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 draw-
able.

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 under-
line. 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.

ATTRIBUTES
See attributes(7) for descriptions of the following attributes: