Introduce QWheelEvent::Phase (Begin, Changed, Ended)

Some platforms (read: OS X) send wheel events without delta to indicate
that scrolling is about to start or has ended. Currently, Qt simply
ignores wheel events that have no delta. This change introduces a new
QWheelEvent attribute that specifies the phase, and makes it possible
to receive the special wheel events in started/ended phases. These
events are required for implementing correctly behaving transient
scrollbars.

Change-Id: Ib8ce0d9ce9be63b2ad60aa7b0aaa1f12ef6cad09
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

1 files changed, 10 insertions, 8 deletions

diff --git a/src/gui/kernel/qwindowsysteminterface.cpp b/src/gui/kernel/qwindowsysteminterface.cpp
index 6fc63fe96c..b9912c1691 100644
--- a/src/gui/kernel/qwindowsysteminterface.cpp
+++ b/src/gui/kernel/qwindowsysteminterface.cpp
@@ -298,13 +298,13 @@ void QWindowSystemInterface::handleWheelEvent(QWindow *tlw, ulong timestamp, con
     handleWheelEvent(tlw, timestamp, local, global, QPoint(), point, mods);
 }
 
-void QWindowSystemInterface::handleWheelEvent(QWindow *w, const QPointF & local, const QPointF & global, QPoint pixelDelta, QPoint angleDelta, Qt::KeyboardModifiers mods)
+void QWindowSystemInterface::handleWheelEvent(QWindow *w, const QPointF & local, const QPointF & global, QPoint pixelDelta, QPoint angleDelta, Qt::KeyboardModifiers mods, QWheelEvent::Phase phase)
 {
     unsigned long time = QWindowSystemInterfacePrivate::eventTime.elapsed();
-    handleWheelEvent(w, time, local, global, pixelDelta, angleDelta, mods);
+    handleWheelEvent(w, time, local, global, pixelDelta, angleDelta, mods, phase);
 }
 
-void QWindowSystemInterface::handleWheelEvent(QWindow *tlw, ulong timestamp, const QPointF & local, const QPointF & global, QPoint pixelDelta, QPoint angleDelta, Qt::KeyboardModifiers mods)
+void QWindowSystemInterface::handleWheelEvent(QWindow *tlw, ulong timestamp, const QPointF & local, const QPointF & global, QPoint pixelDelta, QPoint angleDelta, Qt::KeyboardModifiers mods, QWheelEvent::Phase phase)
 {
     // Qt 4 sends two separate wheel events for horizontal and vertical
     // deltas. For Qt 5 we want to send the deltas in one event, but at the
@@ -315,19 +315,21 @@ void QWindowSystemInterface::handleWheelEvent(QWindow *tlw, ulong timestamp, con
     // Angle deltas must always be sent in addition to pixel deltas.
     QWindowSystemInterfacePrivate::WheelEvent *e;
 
-    if (angleDelta.isNull())
+    // Pass QWheelEvent::Started and QWheelEvent::Ended through
+    // even if the wheel delta is null.
+    if (angleDelta.isNull() && phase == QWheelEvent::Changed)
         return;
 
     // Simple case: vertical deltas only:
     if (angleDelta.y() != 0 && angleDelta.x() == 0) {
-        e = new QWindowSystemInterfacePrivate::WheelEvent(tlw, timestamp, local, global, pixelDelta, angleDelta, angleDelta.y(), Qt::Vertical, mods);
+        e = new QWindowSystemInterfacePrivate::WheelEvent(tlw, timestamp, local, global, pixelDelta, angleDelta, angleDelta.y(), Qt::Vertical, mods, phase);
         QWindowSystemInterfacePrivate::handleWindowSystemEvent(e);
         return;
     }
 
     // Simple case: horizontal deltas only:
     if (angleDelta.y() == 0 && angleDelta.x() != 0) {
-        e = new QWindowSystemInterfacePrivate::WheelEvent(tlw, timestamp, local, global, pixelDelta, angleDelta, angleDelta.x(), Qt::Horizontal, mods);
+        e = new QWindowSystemInterfacePrivate::WheelEvent(tlw, timestamp, local, global, pixelDelta, angleDelta, angleDelta.x(), Qt::Horizontal, mods, phase);
         QWindowSystemInterfacePrivate::handleWindowSystemEvent(e);
         return;
     }
@@ -335,12 +337,12 @@ void QWindowSystemInterface::handleWheelEvent(QWindow *tlw, ulong timestamp, con
     // Both horizontal and vertical deltas: Send two wheel events.
     // The first event contains the Qt 5 pixel and angle delta as points,
     // and in addition the Qt 4 compatibility vertical angle delta.
-    e = new QWindowSystemInterfacePrivate::WheelEvent(tlw, timestamp, local, global, pixelDelta, angleDelta, angleDelta.y(), Qt::Vertical, mods);
+    e = new QWindowSystemInterfacePrivate::WheelEvent(tlw, timestamp, local, global, pixelDelta, angleDelta, angleDelta.y(), Qt::Vertical, mods, phase);
     QWindowSystemInterfacePrivate::handleWindowSystemEvent(e);
 
     // The second event contains null pixel and angle points and the
     // Qt 4 compatibility horizontal angle delta.
-    e = new QWindowSystemInterfacePrivate::WheelEvent(tlw, timestamp, local, global, QPoint(), QPoint(), angleDelta.x(), Qt::Horizontal, mods);
+    e = new QWindowSystemInterfacePrivate::WheelEvent(tlw, timestamp, local, global, QPoint(), QPoint(), angleDelta.x(), Qt::Horizontal, mods, phase);
     QWindowSystemInterfacePrivate::handleWindowSystemEvent(e);
 }