4 files changed, 60 insertions, 24 deletions

diff --git a/src/gui/image/qicon.cpp b/src/gui/image/qicon.cpp
index 7ae081adfb..cebe5ce5f9 100644
--- a/src/gui/image/qicon.cpp
+++ b/src/gui/image/qicon.cpp
@@ -45,6 +45,7 @@
 #include "qcache.h"
 #include "qdebug.h"
 #include "qpalette.h"
+#include "qmath.h"
 
 #include "private/qhexstring_p.h"
 #include "private/qguiapplication_p.h"
@@ -1029,19 +1030,13 @@ void QIcon::addFile(const QString &fileName, const QSize &size, Mode mode, State
             d->engine = new QPixmapIconEngine;
         }
     }
+
     d->engine->addFile(fileName, size, mode, state);
 
-    // Check if a "@2x" file exists and add it.
-    static bool disable2xImageLoading = !qEnvironmentVariableIsEmpty("QT_HIGHDPI_DISABLE_2X_IMAGE_LOADING");
-    if (!disable2xImageLoading && qApp->devicePixelRatio() > 1.0) {
-        QString at2xfileName = fileName;
-        int dotIndex = fileName.lastIndexOf(QLatin1Char('.'));
-        if (dotIndex == -1) /* no dot */
-            dotIndex = fileName.size(); /* append */
-        at2xfileName.insert(dotIndex, QStringLiteral("@2x"));
-        if (QFile::exists(at2xfileName))
-            d->engine->addFile(at2xfileName, size, mode, state);
-    }
+    // Check if a "@Nx" file exists and add it.
+    QString atNxFileName = qt_findAtNxFile(fileName, qApp->devicePixelRatio());
+    if (atNxFileName != fileName)
+        d->engine->addFile(atNxFileName, size, mode, state);
 }
 
 /*!
@@ -1395,5 +1390,39 @@ QDebug operator<<(QDebug dbg, const QIcon &i)
     \internal
 */
 
+/*!
+    \internal
+    \since 5.6
+    Attempts to find a suitable @Nx file for the given \a targetDevicePixelRatio
+    Returns the the \a baseFileName if no such file was found.
+
+    Given base foo.png and a target dpr of 2.5, this function will look for
+    foo@3x.png, then foo@2x, then fall back to foo.png if not found.
+*/
+QString qt_findAtNxFile(const QString &baseFileName, qreal targetDevicePixelRatio)
+{
+    if (targetDevicePixelRatio <= 1.0)
+        return baseFileName;
+
+    static bool disableNxImageLoading = !qEnvironmentVariableIsEmpty("QT_HIGHDPI_DISABLE_2X_IMAGE_LOADING");
+    if (disableNxImageLoading)
+        return baseFileName;
+
+    QString atNx = QLatin1String("@%1x");
+    int dotIndex = baseFileName.lastIndexOf(QLatin1Char('.'));
+    if (dotIndex == -1) /* no dot */
+        dotIndex = baseFileName.size(); /* append */
+
+    // Check for @Nx, ..., @3x, @2x file versions,
+    for (int n = qCeil(targetDevicePixelRatio); n > 1; --n) {
+        QString atNxfileName = baseFileName;
+        atNxfileName.insert(dotIndex, atNx.arg(n));
+        if (QFile::exists(atNxfileName))
+            return atNxfileName;
+    }
+
+    return baseFileName;
+}
+
 QT_END_NAMESPACE
 #endif //QT_NO_ICON
diff --git a/src/gui/image/qicon.h b/src/gui/image/qicon.h
index 329ae3deb3..6808bc2828 100644
--- a/src/gui/image/qicon.h
+++ b/src/gui/image/qicon.h
@@ -140,6 +140,8 @@ Q_GUI_EXPORT QDataStream &operator>>(QDataStream &, QIcon &);
 Q_GUI_EXPORT QDebug operator<<(QDebug dbg, const QIcon &);
 #endif
 
+Q_GUI_EXPORT QString qt_findAtNxFile(const QString &baseFileName, qreal targetDevicePixelRatio);
+
 QT_END_NAMESPACE
 
 #endif // QICON_H
diff --git a/src/gui/image/qpixmap_win.cpp b/src/gui/image/qpixmap_win.cpp
index 12e19440dc..a7a9b375ff 100644
--- a/src/gui/image/qpixmap_win.cpp
+++ b/src/gui/image/qpixmap_win.cpp
@@ -345,9 +345,22 @@ static QImage qt_imageFromWinIconHBITMAP(HDC hdc, HBITMAP bitmap, int w, int h)
     return image;
 }
 
+static inline bool hasAlpha(const QImage &image)
+{
+    const int w = image.width();
+    const int h = image.height();
+    for (int y = 0; y < h; ++y) {
+        const QRgb *scanLine = reinterpret_cast<const QRgb *>(image.scanLine(y));
+        for (int x = 0; x < w; ++x) {
+            if (qAlpha(scanLine[x]) != 0)
+                return true;
+        }
+    }
+    return false;
+}
+
 Q_GUI_EXPORT QPixmap qt_pixmapFromWinHICON(HICON icon)
 {
-    bool foundAlpha = false;
     HDC screenDevice = GetDC(0);
     HDC hdc = CreateCompatibleDC(screenDevice);
     ReleaseDC(0, screenDevice);
@@ -356,6 +369,7 @@ Q_GUI_EXPORT QPixmap qt_pixmapFromWinHICON(HICON icon)
     const bool result = GetIconInfo(icon, &iconinfo); //x and y Hotspot describes the icon center
     if (!result) {
         qErrnoWarning("QPixmap::fromWinHICON(), failed to GetIconInfo()");
+        DeleteDC(hdc);
         return QPixmap();
     }
 
@@ -371,17 +385,7 @@ Q_GUI_EXPORT QPixmap qt_pixmapFromWinHICON(HICON icon)
     DrawIconEx( hdc, 0, 0, icon, iconinfo.xHotspot * 2, iconinfo.yHotspot * 2, 0, 0, DI_NORMAL);
     QImage image = qt_imageFromWinIconHBITMAP(hdc, winBitmap, w, h);
 
-    for (int y = 0 ; y < h && !foundAlpha ; y++) {
-        const QRgb *scanLine= reinterpret_cast<const QRgb *>(image.scanLine(y));
-        for (int x = 0; x < w ; x++) {
-            if (qAlpha(scanLine[x]) != 0) {
-                foundAlpha = true;
-                break;
-            }
-        }
-    }
-    if (!foundAlpha) {
-        //If no alpha was found, we use the mask to set alpha values
+    if (!image.isNull() && !hasAlpha(image)) { //If no alpha was found, we use the mask to set alpha values
         DrawIconEx( hdc, 0, 0, icon, w, h, 0, 0, DI_MASK);
         const QImage mask = qt_imageFromWinIconHBITMAP(hdc, winBitmap, w, h);
 
diff --git a/src/gui/image/qpixmapcache.cpp b/src/gui/image/qpixmapcache.cpp
index 2df813367d..6265a0c16d 100644
--- a/src/gui/image/qpixmapcache.cpp
+++ b/src/gui/image/qpixmapcache.cpp
@@ -652,7 +652,8 @@ void QPixmapCache::remove(const Key &key)
 void QPixmapCache::clear()
 {
     QT_TRY {
-        pm_cache()->clear();
+        if (pm_cache.exists())
+            pm_cache->clear();
     } QT_CATCH(const std::bad_alloc &) {
         // if we ran out of memory during pm_cache(), it's no leak,
         // so just ignore it.