Remove mapping from CJK/Latin to Common script in Harfbuzz NG

The original commit message says this is to ensure compatibility
with the old Harfbuzz, but since OpenType features such as
kerning are often matched based on the writing system of the glyphs,
it will break kerning (and other OpenType features) for text in these
languages in some fonts. Even font that were successfully kerned by
the old Harfbuzz are broken.

To avoid regressing on finding cursor positions inside ligatures,
we need to amend 9f837af9458ea4825b9a8061de444f62d8a7a048. This
would enable cursor positions inside ligatures for languages
where they are only used for cosmetic purposes, and this was
generalized to Common and Greek at the time. This now has to be
expanded to include all the writing systems that were previously
covered by "Common".

[ChangeLog][Text] Fixed kerning error with certain fonts.

Fixes: QTBUG-77908
Change-Id: Id261fef05f86841b1533b7d87207c3d17e01e96e
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 7 insertions, 17 deletions

diff --git a/src/gui/text/qtextengine.cpp b/src/gui/text/qtextengine.cpp
index b37353bf2c..209433dac5 100644
--- a/src/gui/text/qtextengine.cpp
+++ b/src/gui/text/qtextengine.cpp
@@ -2125,22 +2125,7 @@ void QTextEngine::itemize() const
     }
 #if QT_CONFIG(harfbuzz)
     analysis = scriptAnalysis.data();
-    if (qt_useHarfbuzzNG()) {
-        // ### pretend HB-old behavior for now
-        for (int i = 0; i < length; ++i) {
-            switch (analysis[i].script) {
-            case QChar::Script_Latin:
-            case QChar::Script_Hiragana:
-            case QChar::Script_Katakana:
-            case QChar::Script_Bopomofo:
-            case QChar::Script_Han:
-                analysis[i].script = QChar::Script_Common;
-                break;
-            default:
-                break;
-            }
-        }
-    } else {
+    if (!qt_useHarfbuzzNG()) {
         for (int i = 0; i < length; ++i)
             analysis[i].script = hbscript_to_script(script_to_hbscript(analysis[i].script));
     }
@@ -3619,7 +3604,12 @@ int QTextEngine::positionInLigature(const QScriptItem *si, int end,
     int clusterLength = 0;
 
     if (si->analysis.script != QChar::Script_Common &&
-        si->analysis.script != QChar::Script_Greek) {
+        si->analysis.script != QChar::Script_Greek &&
+        si->analysis.script != QChar::Script_Latin &&
+        si->analysis.script != QChar::Script_Hiragana &&
+        si->analysis.script != QChar::Script_Katakana &&
+        si->analysis.script != QChar::Script_Bopomofo &&
+        si->analysis.script != QChar::Script_Han) {
         if (glyph_pos == -1)
             return si->position + end;
         else {