Hide emoji panel if it's not under the mouse cursor

fixes #254
fixes #246

src/emoji/Panel.cc

@@ -39,7 +39,7 @@ Panel::Panel(QWidget *parent)
                       "QScrollBar::handle:vertical { min-height: 30px; }");
 
         setAttribute(Qt::WA_ShowWithoutActivating, true);
-        setWindowFlags(Qt::Popup | Qt::FramelessWindowHint | Qt::NoDropShadowWindowHint);
+        setWindowFlags(Qt::Tool | Qt::FramelessWindowHint | Qt::NoDropShadowWindowHint);
 
         auto mainWidget = new QWidget(this);
         mainWidget->setMaximumSize(width_, height_);
@@ -213,12 +213,6 @@ Panel::showCategory(const Category *category)
         this->scrollArea_->ensureVisible(0, posToGo, 0, 0);
 }
 
-void
-Panel::leaveEvent(QEvent *)
-{
-        hide();
-}
-
 void
 Panel::paintEvent(QPaintEvent *event)
 {

src/emoji/PickButton.cc

@@ -15,15 +15,28 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include "emoji/PickButton.h"
+#include <QDebug>
+
 #include "emoji/Panel.h"
+#include "emoji/PickButton.h"
 
 using namespace emoji;
 
+// Number of milliseconds after which the panel will be hidden
+// if the mouse cursor is not on top of the widget.
+constexpr int TimeoutDuration = 300;
+
 PickButton::PickButton(QWidget *parent)
   : FlatButton(parent)
   , panel_{nullptr}
-{}
+{
+        connect(&hideTimer_, &QTimer::timeout, this, [this]() {
+                if (panel_ && !panel_->underMouse()) {
+                        hideTimer_.stop();
+                        panel_->hide();
+                }
+        });
+}
 
 void
 PickButton::enterEvent(QEvent *e)
@@ -33,8 +46,12 @@ PickButton::enterEvent(QEvent *e)
         if (panel_.isNull()) {
                 panel_ = QSharedPointer<Panel>(new Panel(this));
                 connect(panel_.data(), &Panel::emojiSelected, this, &PickButton::emojiSelected);
+                connect(panel_.data(), &Panel::leaving, this, [this]() { panel_->hide(); });
         }
 
+        if (panel_->isVisible())
+                return;
+
         QPoint pos(rect().x(), rect().y());
         pos = this->mapToGlobal(pos);
 
@@ -46,3 +63,10 @@ PickButton::enterEvent(QEvent *e)
         panel_->move(x, y);
         panel_->show();
 }
+
+void
+PickButton::leaveEvent(QEvent *e)
+{
+        hideTimer_.start(TimeoutDuration);
+        FlatButton::leaveEvent(e);
+}