Add scroll-down button

src/TimelineView.cc

@@ -27,6 +27,7 @@
 #include "MessageEvent.h"
 #include "MessageEventContent.h"
 
+#include "FloatingButton.h"
 #include "ImageItem.h"
 #include "TimelineItem.h"
 #include "TimelineView.h"
@@ -140,6 +141,16 @@ TimelineView::sliderMoved(int position)
         if (!scroll_area_->verticalScrollBar()->isVisible())
                 return;
 
+        const int maxScroll     = scroll_area_->verticalScrollBar()->maximum();
+        const int currentScroll = scroll_area_->verticalScrollBar()->value();
+
+        if (maxScroll - currentScroll > SCROLL_BAR_GAP) {
+                scrollDownBtn_->show();
+                scrollDownBtn_->raise();
+        } else {
+                scrollDownBtn_->hide();
+        }
+
         // The scrollbar is high enough so we can start retrieving old events.
         if (position < SCROLL_BAR_GAP) {
                 if (isTimelineFinished)
@@ -376,6 +387,18 @@ TimelineView::init()
         QSettings settings;
         local_user_ = settings.value("auth/user_id").toString();
 
+        QIcon icon;
+        icon.addFile(":/icons/icons/ui/angle-arrow-down.png");
+        scrollDownBtn_ = new FloatingButton(icon, this);
+        scrollDownBtn_->setBackgroundColor(QColor("#F5F5F5"));
+        scrollDownBtn_->setForegroundColor(QColor("black"));
+        scrollDownBtn_->hide();
+
+        connect(scrollDownBtn_, &QPushButton::clicked, this, [=]() {
+                const int max = scroll_area_->verticalScrollBar()->maximum();
+                scroll_area_->verticalScrollBar()->setValue(max);
+        });
+
         top_layout_ = new QVBoxLayout(this);
         top_layout_->setSpacing(0);
         top_layout_->setMargin(0);

src/ui/FloatingButton.cc

@@ -0,0 +1,95 @@
+#include <QPainterPath>
+
+#include "FloatingButton.h"
+
+FloatingButton::FloatingButton(const QIcon &icon, QWidget *parent)
+  : RaisedButton(parent)
+{
+        setFixedSize(DIAMETER, DIAMETER);
+        setGeometry(buttonGeometry());
+
+        if (parentWidget())
+                parentWidget()->installEventFilter(this);
+
+        setFixedRippleRadius(50);
+        setIcon(icon);
+        raise();
+}
+
+QRect
+FloatingButton::buttonGeometry() const
+{
+        QWidget *parent = parentWidget();
+
+        if (!parent)
+                return QRect();
+
+        return QRect(parent->width() - (OFFSET_X + DIAMETER),
+                     parent->height() - (OFFSET_Y + DIAMETER),
+                     DIAMETER,
+                     DIAMETER);
+}
+
+bool
+FloatingButton::event(QEvent *event)
+{
+        if (!parent())
+                return RaisedButton::event(event);
+
+        switch (event->type()) {
+        case QEvent::ParentChange: {
+                parent()->installEventFilter(this);
+                setGeometry(buttonGeometry());
+                break;
+        }
+        case QEvent::ParentAboutToChange: {
+                parent()->installEventFilter(this);
+                break;
+        }
+        default:
+                break;
+        }
+
+        return RaisedButton::event(event);
+}
+
+bool
+FloatingButton::eventFilter(QObject *obj, QEvent *event)
+{
+        const QEvent::Type type = event->type();
+
+        if (QEvent::Move == type || QEvent::Resize == type)
+                setGeometry(buttonGeometry());
+
+        return RaisedButton::eventFilter(obj, event);
+}
+
+void
+FloatingButton::paintEvent(QPaintEvent *event)
+{
+        Q_UNUSED(event);
+
+        QRect square = QRect(0, 0, DIAMETER, DIAMETER);
+        square.moveCenter(rect().center());
+
+        QPainter p(this);
+        p.setRenderHints(QPainter::Antialiasing);
+
+        QBrush brush;
+        brush.setStyle(Qt::SolidPattern);
+        brush.setColor(backgroundColor());
+
+        p.setBrush(brush);
+        p.setPen(Qt::NoPen);
+        p.drawEllipse(square);
+
+        QRect iconGeometry(0, 0, ICON_SIZE, ICON_SIZE);
+        iconGeometry.moveCenter(square.center());
+
+        QPixmap pixmap = icon().pixmap(QSize(ICON_SIZE, ICON_SIZE));
+        QPainter icon(&pixmap);
+        icon.setCompositionMode(QPainter::CompositionMode_SourceIn);
+        icon.fillRect(pixmap.rect(), foregroundColor());
+
+        p.drawPixmap(iconGeometry, pixmap);
+}