Add drag-open animation

This commit adds an animation for folders that makes clear that
they will open or expand soon. This is the case when the option to
open folders during drag operations is enabled and a user drags an
item on top of a folder.

The animation goes like this:
- Replace the folder's icon with the "folder-open" icon
- Go back to the folder's original icon
- Replace the folder's icon with the "folder-open" icon once more

src/kitemviews/kitemlistcontroller.cpp

@@ -830,6 +830,7 @@ bool KItemListController::dragMoveEvent(QGraphicsSceneDragDropEvent *event, cons
             if (!m_autoActivationTimer->isActive() && m_autoActivationTimer->interval() >= 0) {
                 m_autoActivationTimer->setProperty("index", index);
                 m_autoActivationTimer->start();
+                newHoveredWidget->startActivateSoonAnimation(m_autoActivationTimer->remainingTime());
             }
         } else {
             m_autoActivationTimer->stop();

src/kitemviews/kitemlistwidget.cpp

@@ -438,6 +438,11 @@ QPixmap KItemListWidget::createDragPixmap(const QStyleOptionGraphicsItem *option
     return pixmap;
 }
 
+void KItemListWidget::startActivateSoonAnimation(int timeUntilActivation)
+{
+    Q_UNUSED(timeUntilActivation)
+}
+
 void KItemListWidget::dataChanged(const QHash<QByteArray, QVariant> &current, const QSet<QByteArray> &roles)
 {
     Q_UNUSED(current)

src/kitemviews/kitemlistwidget.h

@@ -188,6 +188,12 @@ public:
      */
     virtual QPixmap createDragPixmap(const QStyleOptionGraphicsItem *option, QWidget *widget = nullptr);
 
+    /**
+     * Starts an animation that makes clear that the item will be activated soon.
+     * @param timeUntilActivation time in milliseconds until the item will activate
+     */
+    virtual void startActivateSoonAnimation(int timeUntilActivation);
+
 Q_SIGNALS:
     void roleEditingCanceled(int index, const QByteArray &role, const QVariant &value);
     void roleEditingFinished(int index, const QByteArray &role, const QVariant &value);

src/kitemviews/kstandarditemlistwidget.cpp

@@ -24,6 +24,7 @@
 #include <QGraphicsView>
 #include <QPixmapCache>
 #include <QStyleOption>
+#include <QVariantAnimation>
 
 // #define KSTANDARDITEMLISTWIDGET_DEBUG
 
@@ -589,6 +590,50 @@ QPixmap KStandardItemListWidget::createDragPixmap(const QStyleOptionGraphicsItem
     return clippedPixmap;
 }
 
+void KStandardItemListWidget::startActivateSoonAnimation(int timeUntilActivation)
+{
+    if (m_activateSoonAnimation) {
+        m_activateSoonAnimation->stop(); // automatically DeleteWhenStopped
+    }
+
+    m_activateSoonAnimation = new QVariantAnimation{this};
+    m_activateSoonAnimation->setStartValue(0.0);
+    m_activateSoonAnimation->setEndValue(1.0);
+    m_activateSoonAnimation->setDuration(timeUntilActivation);
+
+    const QVariant originalIconName{data()["iconName"]};
+    connect(m_activateSoonAnimation, &QVariantAnimation::valueChanged, this, [originalIconName, this](const QVariant &value) {
+        auto progress = value.toFloat();
+
+        QVariant wantedIconName;
+        if (progress < 0.333) {
+            wantedIconName = "folder-open";
+        } else if (progress < 0.666) {
+            wantedIconName = originalIconName;
+        } else {
+            wantedIconName = "folder-open";
+        }
+
+        QHash<QByteArray, QVariant> itemData{data()};
+        if (itemData["iconName"] != wantedIconName) {
+            itemData.insert("iconName", wantedIconName);
+            setData(itemData);
+            invalidateIconCache();
+        }
+    });
+
+    connect(m_activateSoonAnimation, &QObject::destroyed, this, [originalIconName, this]() {
+        QHash<QByteArray, QVariant> itemData{data()};
+        if (itemData["iconName"] == "folder-open") {
+            itemData.insert("iconName", originalIconName);
+            setData(itemData);
+            invalidateIconCache();
+        }
+    });
+
+    m_activateSoonAnimation->start(QAbstractAnimation::DeleteWhenStopped);
+}
+
 KItemListWidgetInformant *KStandardItemListWidget::createInformant()
 {
     return new KStandardItemListWidgetInformant();
@@ -736,7 +781,9 @@ void KStandardItemListWidget::styleOptionChanged(const KItemListStyleOption &cur
 
 void KStandardItemListWidget::hoveredChanged(bool hovered)
 {
-    Q_UNUSED(hovered)
+    if (!hovered && m_activateSoonAnimation) {
+        m_activateSoonAnimation->stop(); // automatically DeleteWhenStopped
+    }
     m_dirtyLayout = true;
 }
 

src/kitemviews/kstandarditemlistwidget.h

@@ -17,6 +17,7 @@
 class KItemListRoleEditor;
 class KItemListStyleOption;
 class KItemListView;
+class QVariantAnimation;
 
 /**
  * @brief standard implementation of the ItemList widget informant for use with KStandardItemListView and KStandardItemModel.
@@ -103,6 +104,8 @@ public:
     QRectF expansionToggleRect() const override;
     QRectF selectionToggleRect() const override;
     QPixmap createDragPixmap(const QStyleOptionGraphicsItem *option, QWidget *widget = nullptr) override;
+    /** @see KItemListWidget::startActivateSoonAnimation() */
+    void startActivateSoonAnimation(int timeUntilActivation) override;
 
     static KItemListWidgetInformant *createInformant();
 
@@ -282,6 +285,9 @@ private:
     KItemListRoleEditor *m_roleEditor;
     KItemListRoleEditor *m_oldRoleEditor;
 
+    /** @see startActivateSoonAnimation() */
+    QPointer<QVariantAnimation> m_activateSoonAnimation;
+
     friend class KStandardItemListWidgetInformant; // Accesses private static methods to be able to
                                                    // share a common layout calculation
 };