1Tk_MeasureChars(3) Tk Library Procedures Tk_MeasureChars(3)
2______________________________________________________________________________
6
8 Tk_MeasureChars, Tk_TextWidth, Tk_DrawChars, Tk_UnderlineChars - rou‐
9 tines to measure and display simple single-line strings.
10
12 #include <tk.h>
13 int
15 Tk_MeasureChars(tkfont, string, numBytes, maxPixels, flags, lengthPtr)
16 int
18 Tk_TextWidth(tkfont, string, numBytes)
19 Tk_DrawChars(display, drawable, gc, tkfont, string, numBytes, x, y)
21 Tk_UnderlineChars(display, drawable, gc, tkfont, string, x, y, firstByte, lastByte)
23
26 Tk_Font tkfont (in) Token for font in which text is to
27 be drawn or measured. Must have
28 been returned by a previous call to
29 Tk_GetFont.
30 const char *string (in) Text to be measured or displayed.
32 Need not be null terminated. Any
33 non-printing meta-characters in the
34 string (such as tabs, newlines, and
35 other control characters) will be
36 measured or displayed in a platform-
37 dependent manner.
38 int numBytes (in) The maximum number of bytes to con‐
40 sider when measuring or drawing
41 string. Must be greater than or
42 equal to 0.
43 int maxPixels (in) If maxPixels is >= 0, it specifies
45 the longest permissible line length
46 in pixels. Characters from string
47 are processed only until this many
48 pixels have been covered. If max‐
49 Pixels is < 0, then the line length
50 is unbounded and the flags argument
51 is ignored.
52 int flags (in) Various flag bits OR-ed together:
54 TK_PARTIAL_OK means include a char‐
55 acter as long as any part of it fits
56 in the length given by maxPixels;
57 otherwise, a character must fit com‐
58 pletely to be considered.
59 TK_WHOLE_WORDS means stop on a word
60 boundary, if possible. If
61 TK_AT_LEAST_ONE is set, it means
62 return at least one character even
63 if no characters could fit in the
64 length given by maxPixels. If
65 TK_AT_LEAST_ONE is set and
66 TK_WHOLE_WORDS is also set, it means
67 that if not even one word fits on
68 the line, return the first few let‐
69 ters of the word that did fit; if
70 not even one letter of the word fit,
71 then the first letter will still be
72 returned.
73 int *lengthPtr (out) Filled with the number of pixels
75 occupied by the number of characters
76 returned as the result of Tk_Mea‐
77 sureChars.
78 Display *display (in) Display on which to draw.
80 Drawable drawable (in) Window or pixmap in which to draw.
82 GC gc (in) Graphics context for drawing charac‐
84 ters. The font selected into this
85 GC must be the same as the tkfont.
86 int x, y (in) Coordinates at which to place the
88 left edge of the baseline when dis‐
89 playing string.
90 int firstByte (in) The index of the first byte of the
92 first character to underline in the
93 string. Underlining begins at the
94 left edge of this character.
95 int lastByte (in) The index of the first byte of the
97 last character up to which the
98 underline will be drawn. The char‐
99 acter specified by lastByte will not
100 itself be underlined.
101______________________________________________________________________________
102
104 These routines are for measuring and displaying simple single-font,
105 single-line strings. To measure and display single-font, multi-line,
106 justified text, refer to the documentation for Tk_ComputeTextLayout.
107 There is no programming interface in the core of Tk that supports
108 multi-font, multi-line text; support for that behavior must be built on
109 top of simpler layers. Note that the interfaces described here are
110 byte-oriented not character-oriented, so index values coming from Tcl
111 scripts need to be converted to byte offsets using the Tcl_UtfAtIndex
112 and related routines.
113 A glyph is the displayable picture of a letter, number, or some other
115 symbol. Not all character codes in a given font have a glyph. Charac‐
116 ters such as tabs, newlines/returns, and control characters that have
117 no glyph are measured and displayed by these procedures in a platform-
118 dependent manner; under X, they are replaced with backslashed escape
119 sequences, while under Windows and Macintosh hollow or solid boxes may
120 be substituted. Refer to the documentation for Tk_ComputeTextLayout
121 for a programming interface that supports the platform-independent
122 expansion of tab characters into columns and newlines/returns into
123 multi-line text.
124 Tk_MeasureChars is used both to compute the length of a given string
126 and to compute how many characters from a string fit in a given amount
127 of space. The return value is the number of bytes from string that fit
128 in the space specified by maxPixels subject to the conditions described
129 by flags. If all characters fit, the return value will be numBytes.
130 *lengthPtr is filled with the computed width, in pixels, of the portion
131 of the string that was measured. For example, if the return value is
132 5, then *lengthPtr is filled with the distance between the left edge of
133 string[0] and the right edge of string[4].
134 Tk_TextWidth is a wrapper function that provides a simpler interface to
136 the Tk_MeasureChars function. The return value is how much space in
137 pixels the given string needs.
138 Tk_DrawChars draws the string at the given location in the given draw‐
140 able.
141 Tk_UnderlineChars underlines the given range of characters in the given
143 string. It does not draw the characters (which are assumed to have
144 been displayed previously by Tk_DrawChars); it just draws the under‐
145 line. This procedure is used to underline a few characters without
146 having to construct an underlined font. To produce natively underlined
147 text, the appropriate underlined font should be constructed and used.
148
150 font(n), FontId(3)
151
153 font, measurement
154Tk 8.1 Tk_MeasureChars(3)