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 mea-
sured. 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 char-
acters) 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 permis-
sible 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_Mea-
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 spec-
ified 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 sup-
ports multi-font, multi-line text; support for that behavior must be built on top of sim-
pler layers. Note that the interfaces described here are byte-oriented not character-ori-
ented, 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 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 and the right edge of string.
Tk_TextWidth is a wrapper function that provides a simpler interface to the Tk_Mea-
sureChars 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.
Tk 8.1 Tk_MeasureChars(3)