Conversion pipeline: Add an option to set the minimum line height of all elemnts as a percentage of the computed font size. By default, calibre now sets the line height to 120% of the computed font size.

src/calibre/ebooks/conversion/cli.py

@@ -120,7 +120,7 @@ def add_pipeline_options(parser, plumber):
                   [
                       'base_font_size', 'disable_font_rescaling',
                       'font_size_mapping',
-                      'line_height',
+                      'line_height', 'minimum_line_height',
                       'linearize_tables',
                       'extra_css', 'smarten_punctuation',
                       'margin_top', 'margin_left', 'margin_right',

src/calibre/ebooks/conversion/plumber.py

@@ -160,13 +160,30 @@ OptionRecommendation(name='disable_font_rescaling',
                    )
         ),
 
+OptionRecommendation(name='minimum_line_height',
+            recommended_value=120.0, level=OptionRecommendation.LOW,
+            help=_(
+            'The minimum line height, as a percentage of the element\'s '
+            'calculated font size. calibre will ensure that every element '
+            'has a line height of at least this setting, irrespective of '
+            'what the input document specifies. Set to zero to disable. '
+            'Default is 120%. Use this setting in preference to '
+            'the direct line height specification, unless you know what '
+            'you are doing. For example, you can achieve "double spaced" '
+            'text by setting this to 240.'
+            )
+        ),
+
 
 OptionRecommendation(name='line_height',
             recommended_value=0, level=OptionRecommendation.LOW,
-            help=_('The line height in pts. Controls spacing between consecutive '
+            help=_(
-                   'lines of text. By default no line height manipulation is '
+            'The line height in pts. Controls spacing between consecutive '
-                   'performed.'
+            'lines of text. Only applies to elements that do not define '
-                   )
+            'their own line height. In most cases, the minimum line height '
+            'option is more useful. '
+            'By default no line height manipulation is performed.'
+            )
         ),
 
 OptionRecommendation(name='linearize_tables',

src/calibre/ebooks/oeb/stylizer.py

@@ -633,12 +633,12 @@ class Style(object):
             parent = self._getparent()
             if 'line-height' in self._style:
                 lineh = self._style['line-height']
+                if lineh == 'normal':
+                    lineh = '1.2'
                 try:
-                    float(lineh)
+                    result = float(lineh) * self.fontSize
                 except ValueError:
                     result = self._unit_convert(lineh, base=self.fontSize)
-                else:
-                    result = float(lineh) * self.fontSize
             elif parent is not None:
                 # TODO: proper inheritance
                 result = parent.lineHeight

src/calibre/ebooks/oeb/transforms/flatcss.py

@@ -245,6 +245,8 @@ class CSSFlattener(object):
             del node.attrib['bgcolor']
         if cssdict.get('font-weight', '').lower() == 'medium':
             cssdict['font-weight'] = 'normal' # ADE chokes on font-weight medium
+
+        fsize = font_size
         if not self.context.disable_font_rescaling:
             _sbase = self.sbase if self.sbase is not None else \
                 self.context.source.fbase
@@ -258,6 +260,14 @@ class CSSFlattener(object):
                 fsize = self.fmap[font_size]
                 cssdict['font-size'] = "%0.5fem" % (fsize / psize)
                 psize = fsize
+
+        try:
+            minlh = self.context.minimum_line_height / 100.
+            if style['line-height'] < minlh * fsize:
+                cssdict['line-height'] = str(minlh)
+        except:
+            self.oeb.logger.exception('Failed to set minimum line-height')
+
         if cssdict:
             if self.lineh and self.fbase and tag != 'body':
                 self.clean_edges(cssdict, style, psize)
@@ -290,6 +300,7 @@ class CSSFlattener(object):
             lineh = self.lineh / psize
             cssdict['line-height'] = "%0.5fem" % lineh
 
+
         if (self.context.remove_paragraph_spacing or
                 self.context.insert_blank_line) and tag in ('p', 'div'):
             if item_id != 'calibre_jacket' or self.context.output_profile.name == 'Kindle':

src/calibre/gui2/convert/look_and_feel.py

@@ -21,7 +21,7 @@ class LookAndFeelWidget(Widget, Ui_Form):
     def __init__(self, parent, get_option, get_help, db=None, book_id=None):
         Widget.__init__(self, parent,
                 ['change_justification', 'extra_css', 'base_font_size',
-                    'font_size_mapping', 'line_height',
+                    'font_size_mapping', 'line_height', 'minimum_line_height',
                     'linearize_tables', 'smarten_punctuation',
                     'disable_font_rescaling', 'insert_blank_line',
                     'remove_paragraph_spacing', 'remove_paragraph_spacing_indent_size','input_encoding',

src/calibre/gui2/convert/look_and_feel.ui

@@ -97,7 +97,7 @@
      </item>
     </layout>
    </item>
-   <item row="3" column="0">
+   <item row="4" column="0">
     <widget class="QLabel" name="label">
      <property name="text">
       <string>Line &amp;height:</string>
@@ -107,7 +107,7 @@
      </property>
     </widget>
    </item>
-   <item row="3" column="1" colspan="2">
+   <item row="4" column="1" colspan="2">
     <widget class="QDoubleSpinBox" name="opt_line_height">
      <property name="suffix">
       <string> pt</string>
@@ -117,7 +117,7 @@
      </property>
     </widget>
    </item>
-   <item row="4" column="0">
+   <item row="5" column="0">
     <widget class="QLabel" name="label_3">
      <property name="text">
       <string>Input character &amp;encoding:</string>
@@ -127,17 +127,17 @@
      </property>
     </widget>
    </item>
-   <item row="4" column="1" colspan="3">
+   <item row="5" column="1" colspan="3">
     <widget class="QLineEdit" name="opt_input_encoding"/>
    </item>
-   <item row="5" column="0" colspan="2">
+   <item row="6" column="0" colspan="2">
     <widget class="QCheckBox" name="opt_remove_paragraph_spacing">
      <property name="text">
       <string>Remove &amp;spacing between paragraphs</string>
      </property>
     </widget>
    </item>
-   <item row="5" column="2" colspan="2">
+   <item row="6" column="2" colspan="2">
     <layout class="QHBoxLayout" name="horizontalLayout_2">
      <item>
       <widget class="QLabel" name="label_4">
@@ -164,21 +164,21 @@
      </item>
     </layout>
    </item>
-   <item row="6" column="0">
+   <item row="7" column="0">
     <widget class="QLabel" name="label_5">
      <property name="text">
       <string>Text justification:</string>
      </property>
     </widget>
    </item>
-   <item row="7" column="0">
+   <item row="8" column="0">
     <widget class="QCheckBox" name="opt_linearize_tables">
      <property name="text">
       <string>&amp;Linearize tables</string>
      </property>
     </widget>
    </item>
-   <item row="10" column="0" colspan="4">
+   <item row="11" column="0" colspan="4">
     <widget class="QGroupBox" name="groupBox">
      <property name="title">
       <string>Extra &amp;CSS</string>
@@ -190,37 +190,60 @@
      </layout>
     </widget>
    </item>
-   <item row="6" column="2" colspan="2">
+   <item row="7" column="2" colspan="2">
     <widget class="QComboBox" name="opt_change_justification"/>
    </item>
-   <item row="7" column="1" colspan="3">
+   <item row="8" column="1" colspan="3">
     <widget class="QCheckBox" name="opt_asciiize">
      <property name="text">
       <string>&amp;Transliterate unicode characters to ASCII</string>
      </property>
     </widget>
    </item>
-   <item row="8" column="0">
+   <item row="9" column="0">
     <widget class="QCheckBox" name="opt_insert_blank_line">
      <property name="text">
       <string>Insert &amp;blank line</string>
      </property>
     </widget>
    </item>
-   <item row="8" column="1" colspan="2">
+   <item row="9" column="1" colspan="2">
     <widget class="QCheckBox" name="opt_keep_ligatures">
      <property name="text">
       <string>Keep &amp;ligatures</string>
      </property>
     </widget>
    </item>
-   <item row="9" column="0">
+   <item row="10" column="0">
     <widget class="QCheckBox" name="opt_smarten_punctuation">
      <property name="text">
       <string>Smarten &amp;punctuation</string>
      </property>
     </widget>
    </item>
+   <item row="3" column="0">
+    <widget class="QLabel" name="label_6">
+     <property name="text">
+      <string>Minimum &amp;line height:</string>
+     </property>
+     <property name="buddy">
+      <cstring>opt_minimum_line_height</cstring>
+     </property>
+    </widget>
+   </item>
+   <item row="3" column="1" colspan="2">
+    <widget class="QDoubleSpinBox" name="opt_minimum_line_height">
+     <property name="suffix">
+      <string> %</string>
+     </property>
+     <property name="decimals">
+      <number>1</number>
+     </property>
+     <property name="maximum">
+      <double>900.000000000000000</double>
+     </property>
+    </widget>
+   </item>
   </layout>
  </widget>
  <resources>