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.
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(3tk), FontId(3tk)
KEYWORDS¶
font, measurement