QIconEngine: move away from virtual_hook usage

Upgrade existing functions to be virtual functions:
  - virtual QString iconName()
  - virtual bool isNull()
  - virtual QPixmap scaledPixmap(...)
  - virtual QList<QSize> availableSizes(...)

Make all of them non-const and remove the const_casts in
the implementation. Keep the default implementation
which calls virtual_hook(), for compatibility.

Note: availableSizes was already virtual, but now loses
the “const”. Port two overrides in the platform themes.

Keep virutal_hook() around for future expansion.

Task-number: QTBUG-85885
Change-Id: I76d0c9f75bfd6ca870c669047d4ef18b82c692e5
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/gui/image/qicon.cpp

@@ -876,10 +876,9 @@ QPixmap QIcon::pixmap(const QSize &size, qreal devicePixelRatio, Mode mode, Stat
     }
 
     // Try get a pixmap that is big enough to be displayed at device pixel resolution.
-    QIconEngine::ScaledPixmapArgument scalePixmapArg = { size * devicePixelRatio, mode, state, devicePixelRatio, QPixmap() };
+    QPixmap pixmap = d->engine->scaledPixmap(size * devicePixelRatio, mode, state, devicePixelRatio);
-    d->engine->virtual_hook(QIconEngine::ScaledPixmapHook, reinterpret_cast<void*>(&scalePixmapArg));
+    pixmap.setDevicePixelRatio(d->pixmapDevicePixelRatio(devicePixelRatio, size, pixmap.size()));
-    scalePixmapArg.pixmap.setDevicePixelRatio(d->pixmapDevicePixelRatio(devicePixelRatio, size, scalePixmapArg.pixmap.size()));
+    return pixmap;
-    return scalePixmapArg.pixmap;
 }
 
 /*!

src/gui/image/qiconengine.cpp

@@ -342,12 +342,12 @@ void QIconEngine::virtual_hook(int id, void *data)
 
     \include qiconengine-virtualhookhelper.qdocinc
  */
-QList<QSize> QIconEngine::availableSizes(QIcon::Mode mode, QIcon::State state) const
+QList<QSize> QIconEngine::availableSizes(QIcon::Mode mode, QIcon::State state)
 {
     AvailableSizesArgument arg;
     arg.mode = mode;
     arg.state = state;
-    const_cast<QIconEngine *>(this)->virtual_hook(QIconEngine::AvailableSizesHook, reinterpret_cast<void*>(&arg));
+    this->virtual_hook(QIconEngine::AvailableSizesHook, reinterpret_cast<void*>(&arg));
     return arg.sizes;
 }
 
@@ -358,10 +358,10 @@ QList<QSize> QIconEngine::availableSizes(QIcon::Mode mode, QIcon::State state) c
 
     \include qiconengine-virtualhookhelper.qdocinc
  */
-QString QIconEngine::iconName() const
+QString QIconEngine::iconName()
 {
     QString name;
-    const_cast<QIconEngine *>(this)->virtual_hook(QIconEngine::IconNameHook, reinterpret_cast<void*>(&name));
+    virtual_hook(QIconEngine::IconNameHook, reinterpret_cast<void*>(&name));
     return name;
 }
 
@@ -372,10 +372,10 @@ QString QIconEngine::iconName() const
 
     \include qiconengine-virtualhookhelper.qdocinc
  */
-bool QIconEngine::isNull() const
+bool QIconEngine::isNull()
 {
     bool isNull = false;
-    const_cast<QIconEngine *>(this)->virtual_hook(QIconEngine::IsNullHook, &isNull);
+    virtual_hook(QIconEngine::IsNullHook, &isNull);
     return isNull;
 }
 

src/gui/image/qiconengine.h

@@ -74,11 +74,11 @@ public:
     };
 
     virtual QList<QSize> availableSizes(QIcon::Mode mode = QIcon::Normal,
-                                    QIcon::State state = QIcon::Off) const;
+                                    QIcon::State state = QIcon::Off);
 
-    virtual QString iconName() const;
+    virtual QString iconName();
-    bool isNull() const; // ### Qt6 make virtual
+    virtual bool isNull();
-    QPixmap scaledPixmap(const QSize &size, QIcon::Mode mode, QIcon::State state, qreal scale); // ### Qt6 make virtual
+    virtual QPixmap scaledPixmap(const QSize &size, QIcon::Mode mode, QIcon::State state, qreal scale);
 
     struct ScaledPixmapArgument
     {
@@ -89,7 +89,6 @@ public:
         QPixmap pixmap;
     };
 
-    // ### Qt6: move content to proper virtual functions
     virtual void virtual_hook(int id, void *data);
 
 protected:

src/plugins/platforms/cocoa/qcocoatheme.mm

@@ -477,7 +477,7 @@ public:
         return QAbstractFileIconEngine::toSizeList(sizes, sizes + sizeof(sizes) / sizeof(sizes[0]));
     }
 
-    QList<QSize> availableSizes(QIcon::Mode = QIcon::Normal, QIcon::State = QIcon::Off) const override
+    QList<QSize> availableSizes(QIcon::Mode = QIcon::Normal, QIcon::State = QIcon::Off) override
     { return QCocoaFileIconEngine::availableIconSizes(); }
 
 protected:

src/plugins/platforms/windows/qwindowstheme.cpp

@@ -888,7 +888,7 @@ public:
     explicit QWindowsFileIconEngine(const QFileInfo &info, QPlatformTheme::IconOptions opts) :
         QAbstractFileIconEngine(info, opts) {}
 
-    QList<QSize> availableSizes(QIcon::Mode = QIcon::Normal, QIcon::State = QIcon::Off) const override
+    QList<QSize> availableSizes(QIcon::Mode = QIcon::Normal, QIcon::State = QIcon::Off) override
     { return QWindowsTheme::instance()->availableFileIconSizes(); }
 
 protected: