PDFlib 8 Windows COM/.NET Tutorial

8.2.8 Controlling the standard Linebreak Algorithm
PDFlib implements a sophisticated line-breaking algorithm. Table 8.2 lists Textflow options
which control the line-breaking algorithm.
Line-breaking rules. When a word or other sequence of text surrounded by space characters
doesn’t fully fit into a line, it must be moved to the next line. In this situation the
line-breaking algorithm decides after which characters a line break is possible.
For example, a formula such as -12+235/8*45 will never be broken, while the string
PDF-345+LIBRARY may be broken to the next line at the minus character. If the text
contains soft hyphen characters it can also be broken after such a character.
For parentheses and quotation marks it depends on whether we have an opening or
closing character: opening parentheses and quotations marks do not offer any break
opportunity. In order to find out whether a quotation mark starts or ends a sequence,
pairs of quotation marks are examined.
Table 8.2 Options for controlling the line-breaking algorithm
option
adjustmethod
advancedlinebreak
avoidbreak
charclass
hyphenchar
explanation
(Keyword) The method used to adjust a line when a text portion doesn’t fit into a line after compressing
or expanding the distance between words subject to the limits specified by the minspacing and maxspacing
options. Default: auto
auto The following methods are applied in order: shrink, spread, nofit, split.
clip
nofit
shrink
split
spread
Same as nofit (see below), except that the long part at the right edge of the fitbox (taking
into account the rightindent option) will be clipped.
The last word will be moved to the next line provided the remaining (short) line will not be
shorter than the percentage specified in the nofitlimit option. Even justified paragraphs
will look slightly ragged in this case.
If a word doesn’t fit in the line the text will be compressed subject to the shrinklimit option
until the word fits. If it still doesn’t fit the nofit method will be applied.
The last word will not be moved to the next line, but will forcefully be hyphenated. For text
fonts a hyphen character will be inserted, but not for symbol fonts.
The last word will be moved to the next line and the remaining (short) line will be justified by
increasing the distance between characters in a word, subject to the spreadlimit option. If
justification still cannot be achieved the nofit method will be applied.
(Boolean) Enable the advanced line breaking algorithm which is required for complex scripts. This is required
for linebreaking in scripts which do not use space characters for designating word boundaries, e.g.
Thai. The options locale and script will be honored. Default: false
(Boolean) If true, avoid any line breaks until avoidbreak is reset to false. Default: false
(List of pairs, where the first element in each pair is a keyword, and the second element is either a unichar
or a list of unichars) The specified unichars will be classified by the specified keyword to determine the
line breaking behaviour of those character(s):
letter behave like a letter (e.g. a B)
punct behave like a punctuation character (e.g. + / ; : )
open behave like an open parenthesis (e.g. [ )
close behave like a close parenthesis (e.g. ] )
default reset all character classes to PDFlib’s builtin defaults
Example: charclass={ close » open « letter {/ : =} punct & }
(Unichar or keyword) Unicode value of the character which replaces a soft hyphen at line breaks. The value
0 and the keyword none completely suppress hyphens. Default: U+00AD (SOFT HYPHEN) if available
in the font, U+002D (HYPHEN-MINUS) otherwise
8.2 Multi-Line Textflows 219