Save previous font engine for right bearing adjustment

In last fix I forgot that fd818312 was for saving and restoring the
right bearing (of last visible glyph) when a LineSeparator was hit
(which can have a different font engine but usually not visble),
thus we can't reset previousGlyph in that case. To make sure we
still get correct right bearing from the font engine used to shape
previousGlyph, we need to save that font engine as well. It does
make the code more complicated than simply saving the right bearing
when a QScriptItem boundary is hit, so hopefully it's an optimization
worth to be made (following e1915815).

Task-number: QTBUG-20423
Reviewed-by: Eskil

1 files changed, 15 insertions, 5 deletions

diff --git a/src/gui/text/qtextlayout.cpp b/src/gui/text/qtextlayout.cpp
index 01adecf..d180f0e 100644
--- a/src/gui/text/qtextlayout.cpp
+++ b/src/gui/text/qtextlayout.cpp
@@ -1715,6 +1715,7 @@ namespace {
         QFixed minimumRightBearing;
 
         QFontEngine *fontEngine;
+        QFontEngine *previousFontEngine;
         const unsigned short *logClusters;
 
         bool manualWrap;
@@ -1735,12 +1736,19 @@ namespace {
             return glyphs.glyphs[logClusters[currentPosition - 1]];
         }
 
-        inline void saveCurrentGlyph()
+        inline void resetPreviousGlyph()
         {
             previousGlyph = 0;
+            previousFontEngine = 0;
+        }
+
+        inline void saveCurrentGlyph()
+        {
+            resetPreviousGlyph();
             if (currentPosition > 0 &&
                 logClusters[currentPosition - 1] < glyphs.numGlyphs) {
                 previousGlyph = currentGlyph(); // needed to calculate right bearing later
+                previousFontEngine = fontEngine;
             }
         }
 
@@ -1760,8 +1768,11 @@ namespace {
 
         inline void adjustPreviousRightBearing()
         {
-            if (previousGlyph > 0)
-                adjustRightBearing(previousGlyph);
+            if (previousGlyph > 0 && previousFontEngine) {
+                qreal rb;
+                previousFontEngine->getGlyphBearings(previousGlyph, 0, &rb);
+                rightBearing = qMin(QFixed(), QFixed::fromReal(rb));
+            }
         }
 
         inline void resetRightBearing()
@@ -1851,7 +1862,7 @@ void QTextLine::layout_helper(int maxGlyphs)
     lbh.currentPosition = line.from;
     int end = 0;
     lbh.logClusters = eng->layoutData->logClustersPtr;
-    lbh.previousGlyph = 0;
+    lbh.resetPreviousGlyph();
 
     while (newItem < eng->layoutData->items.size()) {
         lbh.resetRightBearing();
@@ -1869,7 +1880,6 @@ void QTextLine::layout_helper(int maxGlyphs)
             lbh.currentPosition = qMax(line.from, current.position);
             end = current.position + eng->length(item);
             lbh.glyphs = eng->shapedGlyphs(&current);
-            lbh.previousGlyph = 0;
             QFontEngine *fontEngine = eng->fontEngine(current);
             if (lbh.fontEngine != fontEngine) {
                 lbh.fontEngine = fontEngine;