Minor optimization for QTextLineItemIterator

Don't store unused values (pos_x and levels) and re-use
already calculated ones (itemStart, itemEnd, and itemLength).
Also const-ify some members to make the code a bit more clear.

Change-Id: Ied80ebf9e4e7e8a1d057e413a9bd24f84b8aaf92
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>

src/gui/text/qtextengine.cpp

@@ -3478,15 +3478,15 @@ QTextLineItemIterator::QTextLineItemIterator(QTextEngine *_eng, int _lineNum, co
       logicalItem(-1),
       item(-1),
       visualOrder(nItems),
-      levels(nItems),
       selection(_selection)
 {
-    pos_x = x = QFixed::fromReal(pos.x());
+    x = QFixed::fromReal(pos.x());
 
     x += line.x;
 
     x += eng->alignLine(line);
 
+    QVarLengthArray<uchar> levels(nItems);
     for (int i = 0; i < nItems; ++i)
         levels[i] = eng->layoutData->items[i+firstItem].analysis.bidiLevel;
     QTextEngine::bidiReorder(nItems, levels.data(), visualOrder.data());
@@ -3557,7 +3557,7 @@ bool QTextLineItemIterator::getSelectionBounds(QFixed *selectionX, QFixed *selec
             return false;
 
         int start_glyph = logClusters[from];
-        int end_glyph = (to == eng->length(item)) ? si->num_glyphs : logClusters[to];
+        int end_glyph = (to == itemLength) ? si->num_glyphs : logClusters[to];
         QFixed soff;
         QFixed swidth;
         if (si->analysis.bidiLevel %2) {
@@ -3582,7 +3582,7 @@ bool QTextLineItemIterator::getSelectionBounds(QFixed *selectionX, QFixed *selec
         // If the ending character is also part of a ligature, swidth does
         // not contain that part yet, we also need to find out the width of
         // that left part
-        *selectionWidth += eng->offsetInLigature(si, to, eng->length(item), end_glyph);
+        *selectionWidth += eng->offsetInLigature(si, to, itemLength, end_glyph);
     }
     return true;
 }

src/gui/text/qtextengine_p.h

@@ -676,15 +676,14 @@ struct QTextLineItemIterator
     QTextEngine *eng;
 
     QFixed x;
-    QFixed pos_x;
     const QScriptLine &line;
     QScriptItem *si;
 
-    int lineNum;
-    int lineEnd;
-    int firstItem;
-    int lastItem;
-    int nItems;
+    const int lineNum;
+    const int lineEnd;
+    const int firstItem;
+    const int lastItem;
+    const int nItems;
     int logicalItem;
     int item;
     int itemLength;
@@ -697,7 +696,6 @@ struct QTextLineItemIterator
     QFixed itemWidth;
 
     QVarLengthArray<int> visualOrder;
-    QVarLengthArray<uchar> levels;
 
     const QTextLayout::FormatRange *selection;
 };

src/gui/text/qtextlayout.cpp

@@ -2198,14 +2198,10 @@ QList<QGlyphRun> QTextLine::glyphRuns(int from, int length) const
         if (si.analysis.flags >= QScriptAnalysis::TabOrObject)
             continue;
 
-        QPointF pos(iterator.x.toReal(), y);
-        if (from >= 0 && length >= 0 &&
-            (from >= si.position + eng->length(&si)
-             || from + length <= si.position
-             || from + length <= iterator.itemStart
-             || from >= iterator.itemEnd)) {
+        if (from >= 0 && length >= 0 && (from >= iterator.itemEnd || from + length <= iterator.itemStart))
             continue;
-        }
+
+        QPointF pos(iterator.x.toReal(), y);
 
         QFont font;
         QGlyphRun::GlyphRunFlags flags;
@@ -2226,15 +2222,13 @@ QList<QGlyphRun> QTextLine::glyphRuns(int from, int length) const
         }
 
         int relativeFrom = qMax(iterator.itemStart, from) - si.position;
-        int relativeTo = qMin(iterator.itemEnd - 1, from + length - 1) - si.position;
+        int relativeTo = qMin(iterator.itemEnd, from + length) - 1 - si.position;
 
         unsigned short *logClusters = eng->logClusters(&si);
         int glyphsStart = logClusters[relativeFrom];
-        int glyphsEnd = (relativeTo == eng->length(&si))
-                         ? si.num_glyphs - 1
-                         : logClusters[relativeTo];
+        int glyphsEnd = (relativeTo == iterator.itemLength) ? si.num_glyphs - 1 : logClusters[relativeTo];
         // the glyph index right next to the requested range
-        int nextGlyphIndex = relativeTo < eng->length(&si) - 1 ? logClusters[relativeTo + 1] : si.num_glyphs;
+        int nextGlyphIndex = (relativeTo < iterator.itemLength - 1) ? logClusters[relativeTo + 1] : si.num_glyphs;
         if (nextGlyphIndex - 1 > glyphsEnd)
             glyphsEnd = nextGlyphIndex - 1;
         bool startsInsideLigature = relativeFrom > 0 && logClusters[relativeFrom - 1] == glyphsStart;