OpenGL, PlatformSupport: 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: Ib94d29b6ecec1cdab2604d0277a743e8b340be5e
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/opengl/qgl.cpp

@@ -1264,7 +1264,7 @@ QGLFormat::OpenGLVersionFlags Q_AUTOTEST_EXPORT qOpenGLVersionFlagsFromString(co
     QGLFormat::OpenGLVersionFlags versionFlags = QGLFormat::OpenGL_Version_None;
 
     if (versionString.startsWith(QLatin1String("OpenGL ES"))) {
-        QStringList parts = versionString.split(QLatin1Char(' '));
+        const auto parts = versionString.splitRef(QLatin1Char(' '));
         if (parts.size() >= 3) {
             if (parts[2].startsWith(QLatin1String("1."))) {
                 if (parts[1].endsWith(QLatin1String("-CM"))) {

src/platformsupport/devicediscovery/qdevicediscovery_udev.cpp

@@ -215,8 +215,8 @@ bool QDeviceDiscoveryUDev::checkDeviceType(udev_device *dev)
         return false;
 
     if ((m_types & Device_Keyboard) && (qstrcmp(udev_device_get_property_value(dev, "ID_INPUT_KEYBOARD"), "1") == 0 )) {
-        const char *capabilities_key = udev_device_get_sysattr_value(dev, "capabilities/key");
+        const QString capabilities_key = QString::fromUtf8(udev_device_get_sysattr_value(dev, "capabilities/key"));
-        QStringList val = QString::fromUtf8(capabilities_key).split(QLatin1Char(' '), QString::SkipEmptyParts);
+        const auto val = capabilities_key.splitRef(QLatin1Char(' '), QString::SkipEmptyParts);
         if (!val.isEmpty()) {
             bool ok;
             unsigned long long keys = val.last().toULongLong(&ok, 16);

src/platformsupport/input/evdevkeyboard/qevdevkeyboardhandler.cpp

@@ -101,10 +101,10 @@ QEvdevKeyboardHandler *QEvdevKeyboardHandler::create(const QString &device,
     bool enableCompose = false;
     int grab = 0;
 
-    QStringList args = specification.split(QLatin1Char(':'));
+    const auto args = specification.splitRef(QLatin1Char(':'));
-    foreach (const QString &arg, args) {
+    for (const QStringRef &arg : args) {
         if (arg.startsWith(QLatin1String("keymap=")))
-            keymapFile = arg.mid(7);
+            keymapFile = arg.mid(7).toString();
         else if (arg == QLatin1String("disable-zap"))
             disableZap = true;
         else if (arg == QLatin1String("enable-compose"))

src/platformsupport/input/evdevkeyboard/qevdevkeyboardmanager.cpp

@@ -135,9 +135,10 @@ void QEvdevKeyboardManager::loadKeymap(const QString &file)
         // Restore the default, which is either the built-in keymap or
         // the one given in the plugin spec.
         QString keymapFromSpec;
-        foreach (const QString &arg, m_spec.split(QLatin1Char(':'))) {
+        const auto specs = m_spec.splitRef(QLatin1Char(':'));
+        for (const QStringRef &arg : specs) {
             if (arg.startsWith(QLatin1String("keymap=")))
-                keymapFromSpec = arg.mid(7);
+                keymapFromSpec = arg.mid(7).toString();
         }
         foreach (QEvdevKeyboardHandler *handler, m_keyboards) {
             if (keymapFromSpec.isEmpty())

src/platformsupport/input/evdevmouse/qevdevmousehandler.cpp

@@ -71,8 +71,8 @@ QEvdevMouseHandler *QEvdevMouseHandler::create(const QString &device, const QStr
     int grab = 0;
     bool abs = false;
 
-    QStringList args = specification.split(QLatin1Char(':'));
+    const auto args = specification.splitRef(QLatin1Char(':'));
-    foreach (const QString &arg, args) {
+    for (const QStringRef &arg : args) {
         if (arg == QLatin1String("nocompress"))
             compression = false;
         else if (arg.startsWith(QLatin1String("dejitter=")))

src/platformsupport/themes/genericunix/qgenericunixthemes.cpp

@@ -177,8 +177,9 @@ QStringList QGenericUnixTheme::xdgIconThemePaths()
     QString xdgDirString = QFile::decodeName(qgetenv("XDG_DATA_DIRS"));
     if (xdgDirString.isEmpty())
         xdgDirString = QLatin1String("/usr/local/share/:/usr/share/");
-    foreach (const QString &xdgDir, xdgDirString.split(QLatin1Char(':'))) {
+    const auto xdgDirs = xdgDirString.splitRef(QLatin1Char(':'));
-        const QFileInfo xdgIconsDir(xdgDir + QStringLiteral("/icons"));
+    for (const QStringRef &xdgDir : xdgDirs) {
+        const QFileInfo xdgIconsDir(xdgDir + QLatin1String("/icons"));
         if (xdgIconsDir.isDir())
             paths.append(xdgIconsDir.absoluteFilePath());
     }
@@ -626,7 +627,7 @@ public:
     {
         Q_ASSERT(!systemFont);
         const int split = gtkFontName.lastIndexOf(QChar::Space);
-        float size = gtkFontName.mid(split+1).toFloat();
+        float size = gtkFontName.midRef(split + 1).toFloat();
         QString fontName = gtkFontName.left(split);
 
         systemFont = new QFont(fontName, size);