Support RTL text with merge font engines

Text like Urdu use mixed RTL scripts from Persian, Arabic and so on.
In RTL, sub glyph runs for individual font engines must be added from
end to start, so that the positions can still be calculated in a left
to right manner.

Task-number: QTBUG-23404
Change-Id: I7e55e4b7b858b3abbe94e352c93d36de6226ff58
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@nokia.com>

1 files changed, 10 insertions, 6 deletions

diff --git a/src/gui/text/qtextlayout.cpp b/src/gui/text/qtextlayout.cpp
index f2622a7b20..6cf24d130b 100644
--- a/src/gui/text/qtextlayout.cpp
+++ b/src/gui/text/qtextlayout.cpp
@@ -2264,11 +2264,12 @@ QList<QGlyphRun> QTextLine::glyphRuns(int from, int length) const
             QFontEngine *mainFontEngine = font.d->engineForScript(si.analysis.script);
             if (mainFontEngine->type() == QFontEngine::Multi) {
                 QFontEngineMulti *multiFontEngine = static_cast<QFontEngineMulti *>(mainFontEngine);
-                int start = 0;
-                int end;
-                int which = glyphLayout.glyphs[0] >> 24;
-                for (end = 0; end < glyphLayout.numGlyphs; ++end) {
-                    const int e = glyphLayout.glyphs[end] >> 24;
+                int end = rtl ? glyphLayout.numGlyphs : 0;
+                int start = rtl ? end : 0;
+                int which = glyphLayout.glyphs[rtl ? start - 1 : end] >> 24;
+                for (; (rtl && start > 0) || (!rtl && end < glyphLayout.numGlyphs);
+                     rtl ? --start : ++end) {
+                    const int e = glyphLayout.glyphs[rtl ? start - 1 : end] >> 24;
                     if (e == which)
                         continue;
 
@@ -2286,7 +2287,10 @@ QList<QGlyphRun> QTextLine::glyphRuns(int from, int length) const
                                        subLayout.advances_y[i].toReal());
                     }
 
-                    start = end;
+                    if (rtl)
+                        end = start;
+                    else
+                        start = end;
                     which = e;
                 }