kwineffects: Make OffscreenQuickView generate double click events

Currently, MouseArea.doubleClicked doesn't work in QtQuick effects.
Luckily, the overview effect doesn't use it, but it's still worth making
sure that it works as expected regardless of whether it's a kwin effect.

With this change, the OffscreenQuickView will keep track of the last
mouse press event. If the second button press occurs within the mouse
double click interval, the OffscreenQuickView will generate a
QEvent::MouseButtonDblClick event, similar to what QGuiApplication would
normally do when processing window system events.

src/libkwineffects/kwinoffscreenquickview.cpp

@@ -12,12 +12,14 @@
 #include "kwinglutils.h"
 #include "logging_p.h"
 
+#include <QGuiApplication>
 #include <QQmlEngine>
 #include <QQuickItem>
 #include <QQmlContext>
 #include <QQmlComponent>
 #include <QQuickView>
 #include <QQuickRenderControl>
+#include <QStyleHints>
 
 #include <QOffscreenSurface>
 #include <QOpenGLContext>
@@ -74,6 +76,9 @@ public:
     Qt::TouchPointStates touchState;
     QTouchDevice *touchDevice;
 
+    ulong lastMousePressTime = 0;
+    Qt::MouseButton lastMousePressButton = Qt::NoButton;
+
     void releaseResources();
 
     void updateTouchState(Qt::TouchPointState state, qint32 id, const QPointF& pos);
@@ -270,13 +275,25 @@ void OffscreenQuickView::forwardMouseEvent(QEvent *e)
     case QEvent::MouseMove:
     case QEvent::MouseButtonPress:
     case QEvent::MouseButtonRelease:
-    case QEvent::MouseButtonDblClick:
     {
         QMouseEvent *me = static_cast<QMouseEvent *>(e);
         const QPoint widgetPos = d->m_view->mapFromGlobal(me->pos());
         QMouseEvent cloneEvent(me->type(), widgetPos, me->pos(), me->button(), me->buttons(), me->modifiers());
         QCoreApplication::sendEvent(d->m_view, &cloneEvent);
         e->setAccepted(cloneEvent.isAccepted());
+
+        if (e->type() == QEvent::MouseButtonPress) {
+            const ulong doubleClickInterval = static_cast<ulong>(QGuiApplication::styleHints()->mouseDoubleClickInterval());
+            const bool doubleClick = (me->timestamp() - d->lastMousePressTime < doubleClickInterval) && me->button() == d->lastMousePressButton;
+            d->lastMousePressTime = me->timestamp();
+            d->lastMousePressButton = me->button();
+            if (doubleClick) {
+                d->lastMousePressButton = Qt::NoButton;
+                QMouseEvent doubleClickEvent(QEvent::MouseButtonDblClick, me->localPos(), me->windowPos(), me->screenPos(), me->button(), me->buttons(), me->modifiers());
+                QCoreApplication::sendEvent(d->m_view, &doubleClickEvent);
+            }
+        }
+
         return;
     }
     case QEvent::HoverEnter:

src/plugins/kdecorations/aurorae/src/aurorae.cpp

@@ -30,7 +30,6 @@
 #include <QDirIterator>
 #include <QGuiApplication>
 #include <QLabel>
-#include <QStyleHints>
 #include <QOffscreenSurface>
 #include <QOpenGLContext>
 #include <QOpenGLFramebufferObject>
@@ -517,13 +516,6 @@ void Decoration::mousePressEvent(QMouseEvent *event)
 {
     if (m_view) {
         m_view->forwardMouseEvent(event);
-        if (event->button() == Qt::LeftButton) {
-            if (!m_doubleClickTimer.hasExpired(QGuiApplication::styleHints()->mouseDoubleClickInterval())) {
-                QMouseEvent dc(QEvent::MouseButtonDblClick, event->localPos(), event->windowPos(), event->screenPos(), event->button(), event->buttons(), event->modifiers());
-                m_view->forwardMouseEvent(&dc);
-            }
-        }
-        m_doubleClickTimer.invalidate();
     }
     KDecoration2::Decoration::mousePressEvent(event);
 }
@@ -532,9 +524,6 @@ void Decoration::mouseReleaseEvent(QMouseEvent *event)
 {
     if (m_view) {
         m_view->forwardMouseEvent(event);
-        if (event->isAccepted() && event->button() == Qt::LeftButton) {
-            m_doubleClickTimer.start();
-        }
     }
     KDecoration2::Decoration::mouseReleaseEvent(event);
 }

src/plugins/kdecorations/aurorae/src/aurorae.h

@@ -77,7 +77,6 @@ private:
     QString m_themeName;
 
     KWin::OffscreenQuickView *m_view;
-    QElapsedTimer m_doubleClickTimer;
 };
 
 class ThemeProvider : public KDecoration2::DecorationThemeProvider