Add API to disable text shaping on fonts

In the past, we had an undocumented text flag that worked with
one of the QPainter::drawText() overloads. This was never intended
as public API and served a specific cause in Qt WebKit at one point.

But there is a general need for such API, as disabling shaping features
easily gives 25% performance improvement on text rendering even for
fairly short strings.

This patch adds a new style strategy flag to disable shaping and
will just uses the CMAP and HDMX tables to get glyph indices and advances
for the characters. In Qt 6, the TextBypassShaping flag can be removed
completely and be replaced by the style strategy.

[ChangeLog][QtGui][Text] Added QFont::PreferNoShaping style strategy to support
improvements to performance at the expense of some cosmetic font features.

Task-number: QTBUG-56728
Change-Id: I48e025dcc06afe02824bf5b5011702a7e0036f6d
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index 514e9424b2..1ae2e86a93 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/src/gui/text/qfontengine_p.h
@@ -242,6 +242,12 @@ public:
     void *harfbuzzFace() const;
     bool supportsScript(QChar::Script script) const;
 
+    inline static bool scriptRequiresOpenType(QChar::Script script)
+    {
+        return ((script >= QChar::Script_Syriac && script <= QChar::Script_Sinhala)
+                || script == QChar::Script_Khmer || script == QChar::Script_Nko);
+    }
+
     virtual int getPointInOutline(glyph_t glyph, int flags, quint32 point, QFixed *xpos, QFixed *ypos, quint32 *nPoints);
 
     void clearGlyphCache(const void *key);