From 8d32ce09be2074dfa5dfb52bd9d64bc2f93d5fa2 2017-10-25 07:32:56
From: Thibaud Rabillard <trabillard@itlink.fr>
Date: 2017-10-25 07:32:56
Subject: [PATCH] Manage the scroll of the tab QScrollArea during a drag&drop operation

---

diff --git a/gui/include/DragDropHelper.h b/gui/include/DragDropHelper.h
index d103039..d6b6284 100644
--- a/gui/include/DragDropHelper.h
+++ b/gui/include/DragDropHelper.h
@@ -10,6 +10,31 @@ class VisualizationDragWidget;
 class QMimeData;
 
 /**
+ * @brief Event filter class which manage the scroll of QScrollArea during a drag&drop operation.
+ * @note A QScrollArea inside an other QScrollArea is not fully supported.
+ */
+class DragDropScroller : public QObject
+{
+    Q_OBJECT
+
+public:
+    DragDropScroller(QObject* parent = nullptr);
+
+    void addScrollArea(QScrollArea* scrollArea);
+    void removeScrollArea(QScrollArea* scrollArea);
+
+protected:
+    bool eventFilter(QObject *obj, QEvent *event);
+
+private:
+    class DragDropScrollerPrivate;
+    spimpl::unique_impl_ptr<DragDropScrollerPrivate> impl;
+
+private slots:
+    void onTimer();
+};
+
+/**
  * @brief Helper class for drag&drop operations.
  */
 class DragDropHelper
diff --git a/gui/src/DragDropHelper.cpp b/gui/src/DragDropHelper.cpp
index 9f7cc58..b327352 100644
--- a/gui/src/DragDropHelper.cpp
+++ b/gui/src/DragDropHelper.cpp
@@ -13,6 +13,139 @@
 const QString DragDropHelper::MIME_TYPE_GRAPH = "scqlop/graph";
 const QString DragDropHelper::MIME_TYPE_ZONE = "scqlop/zone";
 
+const int SCROLL_SPEED = 5;
+const int SCROLL_ZONE_SIZE = 50;
+
+struct DragDropScroller::DragDropScrollerPrivate {
+
+    QList<QScrollArea*> m_scrollAreas;
+    QScrollArea* m_currentScrollArea = nullptr;
+    std::unique_ptr<QTimer> m_timer = nullptr;
+
+
+    enum class ScrollDirection {up, down, unknown};
+    ScrollDirection m_direction = ScrollDirection::unknown;
+
+    explicit DragDropScrollerPrivate()
+        : m_timer{std::make_unique<QTimer>()}
+    {
+        m_timer->setInterval(0);
+    }
+};
+
+DragDropScroller::DragDropScroller(QObject* parent)
+    : QObject{parent},  impl{spimpl::make_unique_impl<DragDropScrollerPrivate>()}
+{
+    connect(impl->m_timer.get(), &QTimer::timeout, this, &DragDropScroller::onTimer);
+}
+
+void DragDropScroller::addScrollArea(QScrollArea* scrollArea)
+{
+    impl->m_scrollAreas << scrollArea;
+    scrollArea->viewport()->setAcceptDrops(true);
+}
+
+void DragDropScroller::removeScrollArea(QScrollArea* scrollArea)
+{
+    impl->m_scrollAreas.removeAll(scrollArea);
+    scrollArea->viewport()->setAcceptDrops(false);
+}
+
+bool DragDropScroller::eventFilter(QObject *obj, QEvent *event)
+{
+    if (event->type() == QEvent::DragMove)
+    {
+        auto w = static_cast<QWidget*>(obj);
+
+        if (impl->m_currentScrollArea && impl->m_currentScrollArea->isAncestorOf(w))
+        {
+            auto moveEvent = static_cast<QDragMoveEvent*>(event);
+
+            auto pos = moveEvent->pos();
+            if (impl->m_currentScrollArea->viewport() != w)
+            {
+                auto globalPos = w->mapToGlobal(moveEvent->pos());
+                pos = impl->m_currentScrollArea->viewport()->mapFromGlobal(globalPos);
+            }
+
+            auto isInTopZone = pos.y() > impl->m_currentScrollArea->viewport()->size().height() - SCROLL_ZONE_SIZE;
+            auto isInBottomZone = pos.y() < SCROLL_ZONE_SIZE;
+
+            if (!isInTopZone && !isInBottomZone)
+            {
+                impl->m_direction = DragDropScrollerPrivate::ScrollDirection::unknown;
+                impl->m_timer->stop();
+            }
+            else if (!impl->m_timer->isActive())
+            {
+                impl->m_direction = isInTopZone ? DragDropScrollerPrivate::ScrollDirection::up : DragDropScrollerPrivate::ScrollDirection::down;
+                impl->m_timer->start();
+            }
+        }
+    }
+    else if (event->type() == QEvent::DragEnter)
+    {
+        auto w = static_cast<QWidget*>(obj);
+
+        for (auto scrollArea : impl-> m_scrollAreas)
+        {
+            if (impl->m_currentScrollArea != scrollArea && scrollArea->isAncestorOf(w))
+            {
+                auto enterEvent = static_cast<QDragEnterEvent*>(event);
+                enterEvent->acceptProposedAction();
+                enterEvent->setDropAction(Qt::IgnoreAction);
+                impl->m_currentScrollArea = scrollArea;
+                break;
+            }
+        }
+    }
+    else if (event->type() == QEvent::DragLeave)
+    {
+        auto w = static_cast<QWidget*>(obj);
+        if (impl->m_currentScrollArea)
+        {
+            if (!QRect(QPoint(), impl->m_currentScrollArea->size()).contains(impl->m_currentScrollArea->mapFromGlobal(QCursor::pos())))
+            {
+                impl->m_currentScrollArea = nullptr;
+                impl->m_direction = DragDropScrollerPrivate::ScrollDirection::unknown;
+                impl->m_timer->stop();
+            }
+        }
+    }
+    else if (event->type() == QEvent::Drop)
+    {
+        auto w = static_cast<QWidget*>(obj);
+        if (impl->m_currentScrollArea)
+        {
+            impl->m_currentScrollArea = nullptr;
+            impl->m_direction = DragDropScrollerPrivate::ScrollDirection::unknown;
+            impl->m_timer->stop();
+        }
+    }
+
+    return false;
+}
+
+void DragDropScroller::onTimer()
+{
+    if (impl->m_currentScrollArea)
+    {
+        auto mvt = 0;
+        switch (impl->m_direction)
+        {
+        case DragDropScrollerPrivate::ScrollDirection::up:
+            mvt = SCROLL_SPEED;
+            break;
+        case DragDropScrollerPrivate::ScrollDirection::down:
+            mvt = -SCROLL_SPEED;
+            break;
+        default:
+            break;
+        }
+
+        impl->m_currentScrollArea->verticalScrollBar()->setValue(impl->m_currentScrollArea->verticalScrollBar()->value() + mvt);
+    }
+}
 
 struct DragDropHelper::DragDropHelperPrivate {
 
@@ -97,6 +230,16 @@ bool DragDropHelper::isPlaceHolderSet() const
     return impl->m_placeHolder->parentWidget();
 }
 
+void DragDropHelper::addDragDropScrollArea(QScrollArea *scrollArea)
+{
+   impl->m_dragDropScroller->addScrollArea(scrollArea);
+}
+
+void DragDropHelper::removeDragDropScrollArea(QScrollArea *scrollArea)
+{
+    impl->m_dragDropScroller->removeScrollArea(scrollArea);
+}
+
 QUrl DragDropHelper::imageTemporaryUrl(const QImage& image) const
 {
     image.save(impl->m_imageTempUrl);
diff --git a/gui/src/Visualization/VisualizationTabWidget.cpp b/gui/src/Visualization/VisualizationTabWidget.cpp
index bb4c90d..31df3ea 100644
--- a/gui/src/Visualization/VisualizationTabWidget.cpp
+++ b/gui/src/Visualization/VisualizationTabWidget.cpp
@@ -61,6 +61,7 @@ VisualizationTabWidget::VisualizationTabWidget(const QString &name, QWidget *par
 
     ui->dragDropContainer->setAcceptedMimeTypes({DragDropHelper::MIME_TYPE_GRAPH, DragDropHelper::MIME_TYPE_ZONE});
     connect(ui->dragDropContainer, &VisualizationDragDropContainer::dropOccured, this, &VisualizationTabWidget::dropMimeData);
+    sqpApp->dragDropHelper().addDragDropScrollArea(ui->scrollArea);
 
     // Widget is deleted when closed
     setAttribute(Qt::WA_DeleteOnClose);
@@ -68,6 +69,7 @@ VisualizationTabWidget::VisualizationTabWidget(const QString &name, QWidget *par
 
 VisualizationTabWidget::~VisualizationTabWidget()
 {
+    sqpApp->dragDropHelper().removeDragDropScrollArea(ui->scrollArea);
     delete ui;
 }