cre: configurable kerning method (off/freetype/harfbuzz) (#4167)

Bump base & crengine for HarfBuzz support.

base

@@ -1 +1 @@
-Subproject commit 10d3aa43753d36e6449d54609a949524b7bd1959
+Subproject commit f8cb8ab825a2ccdd962ce7c8b5f03fc5cbcd5267

frontend/apps/reader/modules/readerfont.lua

@@ -147,9 +147,13 @@ function ReaderFont:onReadSettings(config)
     self.ui.document:toggleFontBolder(self.font_embolden)
 
     self.font_hinting = config:readSetting("font_hinting")
-            or G_reader_settings:readSetting("copt_font_hinting") or 2 -- default in cre.cpp
+            or G_reader_settings:readSetting("copt_font_hinting") or 2 -- auto (default in cre.cpp)
     self.ui.document:setFontHinting(self.font_hinting)
 
+    self.font_kerning = config:readSetting("font_kerning")
+            or G_reader_settings:readSetting("copt_font_kerning") or 1 -- freetype (default in cre.cpp)
+    self.ui.document:setFontKerning(self.font_kerning)
+
     self.space_condensing = config:readSetting("space_condensing")
         or G_reader_settings:readSetting("copt_space_condensing") or 75
     self.ui.document:setSpaceCondensing(self.space_condensing)
@@ -254,6 +258,13 @@ function ReaderFont:onSetFontHinting(mode)
     return true
 end
 
+function ReaderFont:onSetFontKerning(mode)
+    self.font_kerning = mode
+    self.ui.document:setFontKerning(mode)
+    self.ui:handleEvent(Event:new("UpdatePos"))
+    return true
+end
+
 function ReaderFont:onSetSpaceCondensing(space)
     self.space_condensing = space
     self.ui.document:setSpaceCondensing(space)
@@ -279,6 +290,7 @@ function ReaderFont:onSaveSettings()
     self.ui.doc_settings:saveSetting("font_size", self.font_size)
     self.ui.doc_settings:saveSetting("font_embolden", self.font_embolden)
     self.ui.doc_settings:saveSetting("font_hinting", self.font_hinting)
+    self.ui.doc_settings:saveSetting("font_kerning", self.font_kerning)
     self.ui.doc_settings:saveSetting("space_condensing", self.space_condensing)
     self.ui.doc_settings:saveSetting("line_space_percent", self.line_space_percent)
     self.ui.doc_settings:saveSetting("gamma_index", self.gamma_index)

frontend/document/credocument.lua

@@ -541,6 +541,11 @@ function CreDocument:setFontHinting(mode)
     self._document:setIntProperty("font.hinting.mode", mode)
 end
 
+function CreDocument:setFontKerning(mode)
+    logger.dbg("CreDocument: set font kerning mode", mode)
+    self._document:setIntProperty("font.kerning.mode", mode)
+end
+
 -- min space condensing percent (how much we can decrease a space width to
 -- make text fit on a line) 25...100%
 function CreDocument:setSpaceCondensing(value)

frontend/ui/data/creoptions.lua

@@ -178,6 +178,23 @@ Note that your selected font size is not affected by this setting.]]),
 - off: no hinting.
 - native: use the font internal hinting instructions.
 - auto: use FreeType's hinting algorithm, ignoring font instructions.]]),
+            },
+            {
+                name = "font_kerning",
+                name_text = S.FONT_KERNING,
+                toggle = {S.OFF, S.FAST, S.ENHANCED},
+                values = {0, 1, 2},
+                default_value = 1,
+                args = {0, 1, 2},
+                event = "SetFontKerning",
+                name_text_hold_callback = optionsutil.showValues,
+                help_text = _([[Font kerning is the process of adjusting the spacing between individual letter forms, to achieve a visually pleasing result.
+
+- off: no kerning.
+- fast: use FreeType's kerning implementation (no ligatures).
+- enhanced: use HarfBuzz's kerning implementation (slower, but may support ligatures with some fonts).
+
+(Font Hinting may need to be adjusted for the best result with either kerning implementation.)]]),
             },
             {
                 name = "space_condensing",

frontend/ui/data/strings.lua

@@ -25,6 +25,7 @@ S.INDENTATION = _("Indentation")
 S.FONT_WEIGHT = _("Font Weight")
 S.GAMMA = _("Gamma")
 S.FONT_HINT = _("Font Hinting")
+S.FONT_KERNING = _("Font Kerning")
 S.VIEW_MODE = _("View Mode")
 S.EMBEDDED_STYLE = _("Embedded Style")
 S.EMBEDDED_FONTS = _("Embedded Fonts")
@@ -48,6 +49,8 @@ S.LIGHTER = _("lighter")
 S.DEFAULT = _("default")
 S.DARKER = _("darker")
 S.NATIVE = _("native")
+S.FAST = _("fast")
+S.ENHANCED = _("enhanced")
 S.LOW = _("low")
 S.HIGH = _("high")
 S.ZERO_DEG = _("0 deg")