qt_findAtNxFile(): account for .9 (9-patch image) extensions

Currently a file with a .9.png extension will only have its @2x variant
found if it follows this format:

foo.9@2x.png

Since ".9" should be considered part of the file suffix, it should
ideally be able to look like this and still be picked up:

foo@2x.9.png

This patch makes qt_findAtNxFile() account for .9.* extensions.

This is needed for the image-based style support in Qt Quick Controls
2, which uses 9-patch images.

qmlbench benchmark results using
benchmarks\auto\creation\quick.image\delegates_image.qml with
QT_SCALE_FACTOR=2 show no difference in performance after this patch
is applied.

[ChangeLog][QtGui] High DPI variants of 9-patch images can now be
loaded using the following syntax: "foo@2x.9.png"

Change-Id: I6d1384113bef21b4fe85a104ee6b16869c93b077
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/gui/image/qicon.cpp

@@ -1469,8 +1469,13 @@ QString qt_findAtNxFile(const QString &baseFileName, qreal targetDevicePixelRati
         return baseFileName;
 
     int dotIndex = baseFileName.lastIndexOf(QLatin1Char('.'));
-    if (dotIndex == -1) /* no dot */
+    if (dotIndex == -1) { /* no dot */
         dotIndex = baseFileName.size(); /* append */
+    } else if (dotIndex >= 2 && baseFileName[dotIndex - 1] == QLatin1Char('9')
+        && baseFileName[dotIndex - 2] == QLatin1Char('.')) {
+        // If the file has a .9.* (9-patch image) extension, we must ensure that the @nx goes before it.
+        dotIndex -= 2;
+    }
 
     QString atNxfileName = baseFileName;
     atNxfileName.insert(dotIndex, QLatin1String("@2x"));

tests/auto/gui/image/qiconhighdpi/tst_qiconhighdpi.cpp

@@ -39,6 +39,7 @@ private slots:
     void initTestCase();
     void fromTheme_data();
     void fromTheme();
+    void ninePatch();
 };
 
 tst_QIconHighDpi::tst_QIconHighDpi()
@@ -182,6 +183,24 @@ void tst_QIconHighDpi::fromTheme()
     QCOMPARE(pixmap.devicePixelRatio(), expectedDpr);
 }
 
+void tst_QIconHighDpi::ninePatch()
+{
+    const QIcon icon(":/icons/misc/button.9.png");
+    const int dpr = qCeil(qApp->devicePixelRatio());
+
+    switch (dpr) {
+    case 1:
+        QCOMPARE(icon.availableSizes().size(), 1);
+        QCOMPARE(icon.availableSizes().at(0), QSize(42, 42));
+        break;
+    case 2:
+        QCOMPARE(icon.availableSizes().size(), 2);
+        QCOMPARE(icon.availableSizes().at(0), QSize(42, 42));
+        QCOMPARE(icon.availableSizes().at(1), QSize(82, 82));
+        break;
+    }
+}
+
 int main(int argc, char *argv[])
 {
     QGuiApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);

tests/auto/gui/image/qiconhighdpi/tst_qiconhighdpi.qrc

@@ -4,5 +4,7 @@
         <file>icons/testtheme/22x22/actions/appointment-new.png</file>
         <file>icons/testtheme/index.theme</file>
         <file>icons/testtheme/22x22@2/actions/appointment-new.png</file>
+        <file>icons/misc/button.9.png</file>
+        <file>icons/misc/button@2x.9.png</file>
     </qresource>
 </RCC>