Force line break after string length

问题:

I want to force a line break after a string length of 14 characters in a PDF generated with AH Formatter. So this is my xsl code without any attempt of line breaking:

<xsl:attribute-set name="big" use-attribute-sets="bold">
  <xsl:attribute name="font-size">38pt</xsl:attribute>
  <xsl:attribute name="line-height">28.84pt</xsl:attribute>
  <xsl:attribute name="text-align">center</xsl:attribute>
  <xsl:attribute name="letter-spacing">1mm</xsl:attribute>
</xsl:attribute-set>

<xsl:attribute-set name="small" use-attribute-sets="bold">
  <xsl:attribute name="font-size">27pt</xsl:attribute>
  <xsl:attribute name="line-height">27pt</xsl:attribute>
  <xsl:attribute name="text-align">center</xsl:attribute>
  <xsl:attribute name="letter-spacing">1mm</xsl:attribute>
</xsl:attribute-set>

<xsl:choose>
   <xsl:when test="string-length($count_cover)>=14">
      <fo:block xsl:use-attribute-sets="small">
         <xsl:apply-templates/>
      </fo:block>
    </xsl:when>
    <xsl:otherwise>          
      <fo:block xsl:use-attribute-sets="big">
         <xsl:apply-templates/>
      </fo:block>
   </xsl:otherwise>
</xsl:choose>

Is it possible to force a line break with XSL-FO?

回答1:

If the title can be converted into string, you can insert <fo:block/> as line break.

<xsl:variable name="cover_title" as="xs:string" select="'Very Long Cover Title! Very Long Cover Title! Very Long Cover Title! '"/>
<xsl:variable name="count_cover" as="xs:integer" select="string-length($cover_title)"/>
<xsl:variable name="lf_position" as="xs:integer" select="14"/>

<xsl:template match="/">
    <xsl:choose>
        <xsl:when test="$count_cover gt $lf_position">
            <fo:block xsl:use-attribute-sets="small">
                <xsl:analyze-string select="$cover_title" regex=".{{1}}">
                    <xsl:matching-substring>
                        <xsl:value-of select="."/>
                        <xsl:if test="position() eq $lf_position">
                            <fo:block/>
                        </xsl:if>
                    </xsl:matching-substring>
                    <xsl:non-matching-substring/>
                </xsl:analyze-string>
            </fo:block>
        </xsl:when>
        <xsl:otherwise>
            <fo:block xsl:use-attribute-sets="big">
                <xsl:value-of select="$cover_title"/>
            </fo:block>
        </xsl:otherwise>
    </xsl:choose>
</xsl:template>

The result:

<fo:block font-weight="bold" font-size="27pt" line-height="27pt" text-align="center" letter-spacing="1mm">Very Long Cove<fo:block/>r Title! Very Long Cover Title! Very Long Cover Title! </fo:block>

However this method ignores word boundaries and hyphenation control. If you are intending to make book cover title, it will better to introduce AH Formatter extensions by using fo:block-container.

1. Use fo:block-container for your title in fixed position and size in the cover page.
2. Set property @overflow="condense" with @axf:overflow-condense=”font-size". https://www.antennahouse.com/product/ahf60/docs/ahf-ext.html#axf.overflow-condense
3. Inside the fo:block-container, place fo:block that stores title contents.
4. You can get desired result because AH Formatter automatically adjust the font-size according to the content volume.

[Example]

<fo:block-container position="absolute" top="..." left="..." width="..." height="..." overflow="condense" axf:overflow-condense="font-size" font-size="27pt" text-align="center">
    <fo:block>
       <fo:inline>Very Long Cover Title! Very Long Cover Title! Very Long Cover Title!</fo:inline>
    </fo:block>
</fo:block-container>

回答2:

1. If you're trying to break words (rather than, e.g., part numbers), then enabling hyphenation may give you a better result than breaking after a fixed number of characters.

2. You can use linefeed-treatment="preserve" and insert 
 instead of fo:block, as this answer to Inserting a line break in a PDF generated from XSL FO using <xsl:value-of> notes. Which you can do with <xsl:value-of select="replace(., '(.{14})', '$1&#xA;')" />

3. You can instead insert a zero-width space, ​, after every 14th character and let AH Formatter break on the zero-width space:

   <xsl:template match="text()"> <xsl:value-of select="replace(replace(., '(\P{Zs}{14})', '$1&#x200B;'), '&#x200B;(\p{Zs})', '$1')" /> </xsl:template>

   The inner replace() inserts the character after every 14 non-space characters, and the outer replace() fixes it if the 15th character was a space character.

   If you're using a proportional-width font, some sequences of 14 characters (excluding, e.g., 14 constant-width lining numbers) will take more or less width than others, so you might want to insert ​ between more characters so that AH Formatter can do its best to fill the line before breaking.

4. You can use axf:word-break="break-all" to enable line breaking even inside a word. See https://www.antennahouse.com/product/ahf63/ahf-ext.html#axf.word-break

回答3:

You can't force a line break in FO, but you can split up the string into separate FO blocks.

<xsl:choose>
  <xsl:when test="string-length($count_cover) &gt;= 14">
    <fo:block><xsl:value-of select="substring($count_cover, 1, 13)"/></fo:block>
    <fo:block><xsl:value-of select="substring($count_cover, 14)"/></fo:block>
  </when>
  <xsl:otherwise>
    <fo:block>
      <xsl:value-of select="$count_cover"/>
    </fo:block>
  </xsl:otherwise>
</xsl:choose>