Use QStringRef to optimize memory allocation

Replace substring functions that return QString with
corresponding functions that return QStringRef where
it's possible.

Create QString from QStringRef only where necessary.

While touching the code, also port loops to C++11 style.

Change-Id: I04c99b24ea6afd3715e3edf9ea00bfab838fd53c
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>
Reviewed-by: Frank Meerkoetter <frank.meerkoetter@basyskom.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@theqtcompany.com>
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>

1 files changed, 15 insertions, 13 deletions

diff --git a/src/quick/items/context2d/qquickcontext2d.cpp b/src/quick/items/context2d/qquickcontext2d.cpp
index 734cadf49a..1b0670aabf 100644
--- a/src/quick/items/context2d/qquickcontext2d.cpp
+++ b/src/quick/items/context2d/qquickcontext2d.cpp
@@ -65,6 +65,7 @@
 #include <private/qv4scopedvalue_p.h>
 
 #include <QtCore/qmath.h>
+#include <QtCore/qvector.h>
 #include <QtCore/private/qnumeric_p.h>
 #include <QtCore/QRunnable>
 #include <QtGui/qguiapplication.h>
@@ -200,7 +201,7 @@ QColor qt_color_from_string(const QV4::Value &name)
     return QColor();
 }
 
-static int qParseFontSizeFromToken(const QString &fontSizeToken, bool &ok)
+static int qParseFontSizeFromToken(const QStringRef &fontSizeToken, bool &ok)
 {
     ok = false;
     float size = fontSizeToken.trimmed().toFloat(&ok);
@@ -216,11 +217,11 @@ static int qParseFontSizeFromToken(const QString &fontSizeToken, bool &ok)
     \c true if successful. If the font size is invalid, \c false is returned
     and a warning is printed.
 */
-static bool qSetFontSizeFromToken(QFont &font, const QString &fontSizeToken)
+static bool qSetFontSizeFromToken(QFont &font, const QStringRef &fontSizeToken)
 {
-    const QString trimmedToken = fontSizeToken.trimmed();
-    const QString unitStr = trimmedToken.right(2);
-    const QString value = trimmedToken.left(trimmedToken.size() - 2);
+    const QStringRef trimmedToken = fontSizeToken.trimmed();
+    const QStringRef unitStr = trimmedToken.right(2);
+    const QStringRef value = trimmedToken.left(trimmedToken.size() - 2);
     bool ok = false;
     int size = 0;
     if (unitStr == QLatin1String("px")) {
@@ -246,7 +247,7 @@ static bool qSetFontSizeFromToken(QFont &font, const QString &fontSizeToken)
     each family is separated by spaces. Families with spaces in their name
     must be quoted.
 */
-static QStringList qExtractFontFamiliesFromString(const QString &fontFamiliesString)
+static QStringList qExtractFontFamiliesFromString(const QStringRef &fontFamiliesString)
 {
     QStringList extractedFamilies;
     int quoteIndex = -1;
@@ -259,7 +260,7 @@ static QStringList qExtractFontFamiliesFromString(const QString &fontFamiliesStr
             } else {
                 if (ch == fontFamiliesString.at(quoteIndex)) {
                     // Found the matching quote. +1/-1 because we don't want the quote as part of the name.
-                    const QString family = fontFamiliesString.mid(quoteIndex + 1, index - quoteIndex - 1);
+                    const QString family = fontFamiliesString.mid(quoteIndex + 1, index - quoteIndex - 1).toString();
                     extractedFamilies.push_back(family);
                     currentFamily.clear();
                     quoteIndex = -1;
@@ -390,16 +391,17 @@ static QFont qt_font_from_string(const QString& fontString, const QFont &current
     fontSizeEnd += 3;
 
     QFont newFont;
-    if (!qSetFontSizeFromToken(newFont, fontString.mid(fontSizeStart, fontSizeEnd - fontSizeStart)))
+    if (!qSetFontSizeFromToken(newFont, fontString.midRef(fontSizeStart, fontSizeEnd - fontSizeStart)))
         return currentFont;
 
     // We don't want to parse the size twice, so remove it now.
     QString remainingFontString = fontString;
     remainingFontString.remove(fontSizeStart, fontSizeEnd - fontSizeStart);
+    QStringRef remainingFontStringRef(&remainingFontString);
 
     // Next, we have to take any font families out, as QString::split() will ruin quoted family names.
-    const QString fontFamiliesString = remainingFontString.mid(fontSizeStart);
-    remainingFontString.chop(remainingFontString.length() - fontSizeStart);
+    const QStringRef fontFamiliesString = remainingFontStringRef.mid(fontSizeStart);
+    remainingFontStringRef.truncate(fontSizeStart);
     QStringList fontFamilies = qExtractFontFamiliesFromString(fontFamiliesString);
     if (fontFamilies.isEmpty()) {
         return currentFont;
@@ -408,16 +410,16 @@ static QFont qt_font_from_string(const QString& fontString, const QFont &current
         return currentFont;
 
     // Now that we've removed the messy parts, we can split the font string on spaces.
-    const QString trimmedTokensStr = remainingFontString.trimmed();
+    const QStringRef trimmedTokensStr = remainingFontStringRef.trimmed();
     if (trimmedTokensStr.isEmpty()) {
         // No optional properties.
         return newFont;
     }
-    const QStringList tokens = trimmedTokensStr.split(QLatin1Char(' '));
+    const auto tokens = trimmedTokensStr.split(QLatin1Char(' '));
 
     int usedTokens = NoTokens;
     // Optional properties can be in any order, but font-size and font-family must be last.
-    for (const QString &token : tokens) {
+    for (const QStringRef &token : tokens) {
         if (token.compare(QLatin1String("normal")) == 0) {
             if (!(usedTokens & FontStyle) || !(usedTokens & FontVariant) || !(usedTokens & FontWeight)) {
                 // Could be font-style, font-variant or font-weight.