DragonFly On-Line Manual Pages
Tk_MeasureChars(3) Tk Library Procedures Tk_MeasureChars(3)
Tk_MeasureChars, Tk_TextWidth, Tk_DrawChars, Tk_UnderlineChars -
routines to measure and display simple single-line strings.
Tk_MeasureChars(tkfont, string, numBytes, maxPixels, flags, lengthPtr)
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)
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
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-
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
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
int x, y (in) Coordinates at which to place the
left edge of the baseline when
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.
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 and the right edge of string.
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
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
Tk 8.1 Tk_MeasureChars(3)