[Mac] Attempt to fix slow scrolling on Apple trackpads.

Closes #832

src/lib/lib.pro

@@ -470,8 +470,10 @@ win32 {
 }
 
 mac {
-    HEADERS += other/macmenureceiver.h
-    SOURCES += other/macmenureceiver.cpp
+    HEADERS += other/macmenureceiver.h \
+               webview/macwebviewscroller.h
+    SOURCES += other/macmenureceiver.cpp \
+               webview/macwebviewscroller.cpp
     RESOURCES -= data/certs.qrc
 
     LIBS += -framework CoreServices

src/lib/webview/macwebviewscroller.cpp

@@ -0,0 +1,68 @@
+/* ============================================================
+* QupZilla - WebKit based browser
+* Copyright (C) 2013  David Rosca <nowrep@gmail.com>
+*
+* This program is free software: you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation, either version 3 of the License, or
+* (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with this program.  If not, see <http://www.gnu.org/licenses/>.
+* ============================================================ */
+#include "macwebviewscroller.h"
+#include "webview.h"
+
+#include <QApplication>
+#include <QWheelEvent>
+#include <QTimer>
+
+// Workaround for QTBUG-22269 (Extremely slow scrolling on Apple trackpads)
+// https://bugreports.qt-project.org/browse/QTBUG-22269
+
+MacWebViewScroller::MacWebViewScroller(WebView* view)
+    : QObject(view)
+    , m_view(view)
+    , m_timerRunning(false)
+    , m_delta(0)
+{
+    view->installEventFilter(this);
+}
+
+bool MacWebViewScroller::eventFilter(QObject* obj, QEvent* event)
+{
+    if (obj != m_view || event->type() != QEvent::Wheel) {
+        return false;
+    }
+
+    QWheelEvent* ev = static_cast<QWheelEvent*>(event);
+    if (ev->buttons() != Qt::NoButton || ev->modifiers() != Qt::NoModifier) {
+        return false;
+    }
+
+    if (!m_timerRunning) {
+        m_delta = ev->delta();
+        m_pos = ev->pos();
+        m_globalPos = ev->globalPos();
+
+        QTimer::singleShot(25, this, SLOT(sendWheelEvent()));
+        m_timerRunning = true;
+    }
+    else {
+        m_delta += ev->delta();
+    }
+
+    return true;
+}
+
+void MacWebViewScroller::sendWheelEvent()
+{
+    QWheelEvent ev(m_pos, m_delta, Qt::NoButton, Qt::NoModifier);
+    m_view->event(&ev);
+    m_timerRunning = false;
+}

src/lib/webview/macwebviewscroller.h

@@ -0,0 +1,49 @@
+/* ============================================================
+* QupZilla - WebKit based browser
+* Copyright (C) 2013  David Rosca <nowrep@gmail.com>
+*
+* This program is free software: you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation, either version 3 of the License, or
+* (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with this program.  If not, see <http://www.gnu.org/licenses/>.
+* ============================================================ */
+#ifndef MACWEBVIEWSCROLLER_H
+#define MACWEBVIEWSCROLLER_H
+
+#include <QObject>
+#include <QPoint>
+
+class QWheelEvent;
+
+class WebView;
+
+class MacWebViewScroller : public QObject
+{
+    Q_OBJECT
+public:
+    explicit MacWebViewScroller(WebView* view);
+
+    bool eventFilter(QObject* obj, QEvent* event);
+
+private slots:
+    void sendWheelEvent();
+
+private:
+    WebView* m_view;
+
+    bool m_timerRunning;
+    int m_delta;
+    QPoint m_pos;
+    QPoint m_globalPos;
+
+};
+
+#endif // MACWEBVIEWSCROLLER_H

src/lib/webview/webview.cpp

@@ -37,6 +37,10 @@
 #include "qtwebkit/spellcheck/speller.h"
 #endif
 
+#ifdef Q_OS_MAC
+#include "macwebviewscroller.h"
+#endif
+
 #include <QDir>
 #include <QTimer>
 #include <QDesktopServices>
@@ -74,6 +78,10 @@ WebView::WebView(QWidget* parent)
 #if QTWEBKIT_TO_2_3
     installEventFilter(this);
 #endif
+
+#ifdef Q_OS_MAC
+    new MacWebViewScroller(this);
+#endif
 }
 
 QIcon WebView::icon() const