Optimize QTextEngine::findItem() usage cases

Since the item positions are guaranteed to grow, we could safely re-use
the obtained first item while looking for the last item in the chain.

Change-Id: I5e42f5de820c62a51a109a4b227b031c697aa898
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

3 files changed, 10 insertions, 9 deletions

diff --git a/src/gui/text/qtextengine.cpp b/src/gui/text/qtextengine.cpp
index 50a242d81e..31b1109b6a 100644
--- a/src/gui/text/qtextengine.cpp
+++ b/src/gui/text/qtextengine.cpp
@@ -918,10 +918,11 @@ void QTextEngine::shapeLine(const QScriptLine &line)
 {
     QFixed x;
     bool first = true;
-    const int end = findItem(line.from + line.length - 1);
     int item = findItem(line.from);
     if (item == -1)
         return;
+
+    const int end = findItem(line.from + line.length - 1, item);
     for ( ; item <= end; ++item) {
         QScriptItem &si = layoutData->items[item];
         if (si.analysis.flags == QScriptAnalysis::Tab) {
@@ -1747,13 +1748,13 @@ bool QTextEngine::isRightToLeft() const
 }
 
 
-int QTextEngine::findItem(int strPos) const
+int QTextEngine::findItem(int strPos, int firstItem) const
 {
     itemize();
-    if (strPos < 0 || strPos >= layoutData->string.size())
+    if (strPos < 0 || strPos >= layoutData->string.size() || firstItem < 0)
         return -1;
 
-    int left = 1;
+    int left = firstItem + 1;
     int right = layoutData->items.size()-1;
     while(left <= right) {
         int middle = ((right-left)/2)+left;
@@ -2172,7 +2173,7 @@ void QTextEngine::justify(const QScriptLine &line)
         return;
 
     int firstItem = findItem(line.from);
-    int lastItem = findItem(line.from + line_length - 1);
+    int lastItem = findItem(line.from + line_length - 1, firstItem);
     int nItems = (firstItem >= 0 && lastItem >= firstItem)? (lastItem-firstItem+1) : 0;
 
     QVarLengthArray<QJustificationPoint> justificationPoints;
@@ -3529,7 +3530,7 @@ QTextLineItemIterator::QTextLineItemIterator(QTextEngine *_eng, int _lineNum, co
       lineNum(_lineNum),
       lineEnd(line.from + line.length),
       firstItem(eng->findItem(line.from)),
-      lastItem(eng->findItem(lineEnd - 1)),
+      lastItem(eng->findItem(lineEnd - 1, firstItem)),
       nItems((firstItem >= 0 && lastItem >= firstItem)? (lastItem-firstItem+1) : 0),
       logicalItem(-1),
       item(-1),
diff --git a/src/gui/text/qtextengine_p.h b/src/gui/text/qtextengine_p.h
index dbe8e1ee2b..39c228fd52 100644
--- a/src/gui/text/qtextengine_p.h
+++ b/src/gui/text/qtextengine_p.h
@@ -512,7 +512,7 @@ public:
 
     void freeMemory();
 
-    int findItem(int strPos) const;
+    int findItem(int strPos, int firstItem = 0) const;
     inline QTextFormatCollection *formatCollection() const {
         if (block.docHandle())
             return block.docHandle()->formatCollection();
diff --git a/src/gui/text/qtextlayout.cpp b/src/gui/text/qtextlayout.cpp
index 67af3d316b..5f570fea82 100644
--- a/src/gui/text/qtextlayout.cpp
+++ b/src/gui/text/qtextlayout.cpp
@@ -2685,7 +2685,7 @@ qreal QTextLine::cursorToX(int *cursorPos, Edge edge) const
     // add the items left of the cursor
 
     int firstItem = eng->findItem(line.from);
-    int lastItem = eng->findItem(lineEnd - 1);
+    int lastItem = eng->findItem(lineEnd - 1, itm);
     int nItems = (firstItem >= 0 && lastItem >= firstItem)? (lastItem-firstItem+1) : 0;
 
     QVarLengthArray<int> visualOrder(nItems);
@@ -2786,7 +2786,7 @@ int QTextLine::xToCursor(qreal _x, CursorPosition cpos) const
         return line.from;
 
     int firstItem = eng->findItem(line.from);
-    int lastItem = eng->findItem(line.from + line_length - 1);
+    int lastItem = eng->findItem(line.from + line_length - 1, firstItem);
     int nItems = (firstItem >= 0 && lastItem >= firstItem)? (lastItem-firstItem+1) : 0;
 
     if (!nItems)