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

1 files changed, 48 insertions, 1 deletions

diff --git a/src/kitemviews/kstandarditemlistwidget.cpp b/src/kitemviews/kstandarditemlistwidget.cpp
index 2a28d198a..b534338ce 100644
--- a/src/kitemviews/kstandarditemlistwidget.cpp
+++ b/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;
 }