Implement support for wheel delta with finer resolution than 15 deg.

At the moment, Qt, in many places, does not really understand that
a mouse wheel, or touch pad, might operate on a much higher
granularity than 15 degrees (that is, a delta of 120). This is clear
disadvantage on mac, since the mighty mouse, and track pad, got a
resolution that is close to 1 degree. This is called pixel scrolling.

This patch first and formost changes the implementation of
QAbstractSlider::wheelEvent to _really_ understand what to do when
delta is less than 120. Rather than accumulate delta until 120
is reached, then scroll with a value equal to:
offset * step * QApplication::wheelScrollLines (default = 3), we
multiply offset directly, before waiting for 120. This means that
event tough offset is below 120, multiplying it with wheelScrollLines
and step will very often give a value over 120, menaing we can scroll
much earlier and _much more_ fined grained. This also fixes some
auto tests that was ifdeffed out because of specialised mac code
written inside this function from before.
(NB: we still plan to introduce a new event for pixel scrolling,
perhaps for Qt-4.7)

Rev-By: Andreas
Rev-By: denis

4 files changed, 38 insertions, 71 deletions

diff --git a/src/gui/kernel/qapplication.cpp b/src/gui/kernel/qapplication.cpp
index 7c38d4b..85b055e 100644
--- a/src/gui/kernel/qapplication.cpp
+++ b/src/gui/kernel/qapplication.cpp
@@ -940,12 +940,8 @@ void QApplicationPrivate::initialize()
     graphics_system = QGraphicsSystemFactory::create(graphics_system_name);
 #endif
 #ifndef QT_NO_WHEELEVENT
-#ifdef Q_OS_MAC
-    QApplicationPrivate::wheel_scroll_lines = 1;
-#else
     QApplicationPrivate::wheel_scroll_lines = 3;
 #endif
-#endif
 
     initializeMultitouch();
 }
diff --git a/src/gui/kernel/qapplication_mac.mm b/src/gui/kernel/qapplication_mac.mm
index 771cddc..84e0d50 100644
--- a/src/gui/kernel/qapplication_mac.mm
+++ b/src/gui/kernel/qapplication_mac.mm
@@ -1697,15 +1697,14 @@ QApplicationPrivate::globalEventProcessor(EventHandlerCallRef er, EventRef event
             // (actually two events; one for horizontal and one for vertical).
             // As a results of this, and to make sure we dont't receive duplicate events,
             // we try to detect when this happend by checking the 'compatibilityEvent'. 
-            const int scrollFactor = 4 * 8;
             SInt32 mdelt = 0;
             GetEventParameter(event, kEventParamMouseWheelSmoothHorizontalDelta, typeSInt32, 0,
                               sizeof(mdelt), 0, &mdelt);
-            wheel_deltaX = mdelt * scrollFactor;
+            wheel_deltaX = mdelt;
             mdelt = 0;
             GetEventParameter(event, kEventParamMouseWheelSmoothVerticalDelta, typeSInt32, 0,
                               sizeof(mdelt), 0, &mdelt);
-            wheel_deltaY = mdelt * scrollFactor;
+            wheel_deltaY = mdelt;
             GetEventParameter(event, kEventParamEventRef, typeEventRef, 0,
                               sizeof(compatibilityEvent), 0, &compatibilityEvent);
         } else if (ekind == kEventMouseWheelMoved) {
@@ -1718,31 +1717,11 @@ QApplicationPrivate::globalEventProcessor(EventHandlerCallRef er, EventRef event
                 GetEventParameter(event, kEventParamMouseWheelAxis, typeMouseWheelAxis, 0,
                         sizeof(axis), 0, &axis);
 
-                // The 'new' event has acceleration applied by the OS, while the old (on
-                // Carbon only), has not. So we introduce acceleration here to be consistent.
-                // The acceleration is trying to respect both pixel based and line scrolling,
-                // which turns out to be rather difficult.
-                int linesToScroll = mdelt > 0 ? 1 : -1;
-                static QTime t;
-                int elapsed = t.elapsed();
-                t.restart();
-                if (elapsed < 20)
-                    linesToScroll *= 120;
-                else if (elapsed < 30)
-                    linesToScroll *= 60;
-                else if (elapsed < 50)
-                    linesToScroll *= 30;
-                else if (elapsed < 100)
-                    linesToScroll *= 6;
-                else if (elapsed < 200)
-                    linesToScroll *= 3;
-                else if (elapsed < 300)
-                    linesToScroll *= 2;
-
+                // Remove acceleration, and use either -120 or 120 as delta:
                 if (axis == kEventMouseWheelAxisX)
-                    wheel_deltaX = linesToScroll * 120;
+                    wheel_deltaX = qBound(-120, int(mdelt * 10000), 120);
                 else
-                    wheel_deltaY = linesToScroll * 120;
+                    wheel_deltaY = qBound(-120, int(mdelt * 10000), 120);
             }
         }
 
@@ -2695,11 +2674,7 @@ int QApplication::keyboardInputInterval()
 
 void QApplication::setWheelScrollLines(int n)
 {
-    Q_UNUSED(n);
-    // On Mac, acceleration is handled by the OS. Multiplying wheel scroll
-    // deltas with n will not be as cross platform as one might think! So
-    // we choose to go native in this case (and let wheel_scroll_lines == 1).
-    //    QApplicationPrivate::wheel_scroll_lines = n;
+    QApplicationPrivate::wheel_scroll_lines = n;
 }
 
 int QApplication::wheelScrollLines()
diff --git a/src/gui/kernel/qcocoaview_mac.mm b/src/gui/kernel/qcocoaview_mac.mm
index d49c150..ecc6bc9 100644
--- a/src/gui/kernel/qcocoaview_mac.mm
+++ b/src/gui/kernel/qcocoaview_mac.mm
@@ -795,23 +795,23 @@ extern "C" {
 
     const EventRef carbonEvent = (EventRef)[theEvent eventRef];
     const UInt32 carbonEventKind = carbonEvent ? ::GetEventKind(carbonEvent) : 0;
-    if (carbonEventKind == kEventMouseScroll) {
+    const bool scrollEvent = carbonEventKind == kEventMouseScroll;
+
+    if (scrollEvent) {
         // The mouse device containts pixel scroll wheel support (Mighty Mouse, Trackpad).
         // Since deviceDelta is delivered as pixels rather than degrees, we need to
         // convert from pixels to degrees in a sensible manner.
         // It looks like four degrees per pixel behaves most native.
         // Qt expects the unit for delta to be 1/8 of a degree:
-        const int scrollFactor = 4 * 8;
-        deltaX = (int)[theEvent deviceDeltaX] * scrollFactor;
-        deltaY = (int)[theEvent deviceDeltaY] * scrollFactor;
-        deltaZ = (int)[theEvent deviceDeltaZ] * scrollFactor;
-    } else { // carbonEventKind == kEventMouseWheelMoved
-        // Mouse wheel deltas seem to tick in at increments of 0.1.
-        // Qt widgets expect the delta to be a multiple of 120.
-        const int scrollFactor = 10 * 120;
-        deltaX = [theEvent deltaX] * scrollFactor;
-        deltaY = [theEvent deltaY] * scrollFactor;
-        deltaZ = [theEvent deltaZ] * scrollFactor;
+        deltaX = [theEvent deviceDeltaX];
+        deltaY = [theEvent deviceDeltaY];
+        deltaZ = [theEvent deviceDeltaZ];
+    } else {
+        // carbonEventKind == kEventMouseWheelMoved
+        // Remove acceleration, and use either -120 or 120 as delta:
+        deltaX = qBound(-120, int([theEvent deltaX] * 10000), 120);
+        deltaY = qBound(-120, int([theEvent deltaY] * 10000), 120);
+        deltaZ = qBound(-120, int([theEvent deltaZ] * 10000), 120);
     }
 
     if (deltaX != 0) {
diff --git a/src/gui/widgets/qabstractslider.cpp b/src/gui/widgets/qabstractslider.cpp
index 588a48e..fec9fab 100644
--- a/src/gui/widgets/qabstractslider.cpp
+++ b/src/gui/widgets/qabstractslider.cpp
@@ -693,29 +693,27 @@ void QAbstractSlider::wheelEvent(QWheelEvent * e)
     if (e->orientation() != d->orientation && !rect().contains(e->pos()))
         return;
 
-    qreal currentOffset = qreal(e->delta()) / 120;
-    d->offset_accumulated += currentOffset;
-    if (int(d->offset_accumulated) == 0) {
-        // QAbstractSlider works on integer values. So if the accumulated
-        // offset is less than +/- 1, we need to wait until we get more
-        // wheel events (this means that the wheel resolution is higher than 
-        // 15 degrees, e.g. when using mac mighty mouse/trackpad):
-        return;
-    }
+    int stepsToScroll = 0;
+    qreal offset = qreal(e->delta()) / 120;
 
-    int stepsToScroll;
     if ((e->modifiers() & Qt::ControlModifier) || (e->modifiers() & Qt::ShiftModifier)) {
-        stepsToScroll = currentOffset > 0 ? d->pageStep : -d->pageStep;
+        // Scroll one page regardless of delta:
+        stepsToScroll = qBound(-d->pageStep, int(offset * d->pageStep), d->pageStep);
+        d->offset_accumulated = 0;
     } else {
-        // Calculate the number of steps to scroll (per 15 degrees of rotate):
-#ifdef Q_OS_MAC
-        // On mac, since mouse wheel scrolling is accelerated and
-        // fine tuned by the OS, we skip applying acceleration:
-        stepsToScroll = int(d->offset_accumulated);
-#else
-        stepsToScroll = int(d->offset_accumulated) * QApplication::wheelScrollLines() * d->singleStep;
-#endif
-        stepsToScroll = qBound(-d->pageStep, stepsToScroll, d->pageStep);
+        // Calculate how many lines to scroll. Depending on what delta is (and 
+        // offset), we might end up with a fraction (e.g. scroll 1.3 lines). We can
+        // only scroll whole lines, so we keep the reminder until next event.
+        qreal stepsToScrollF = offset * QApplication::wheelScrollLines() * d->singleStep;
+        // Check if wheel changed direction since last event:
+        if (d->offset_accumulated != 0 && (offset / d->offset_accumulated) < 0)
+            d->offset_accumulated = 0;
+
+        d->offset_accumulated += stepsToScrollF;
+        stepsToScroll = qBound(-d->pageStep, int(d->offset_accumulated), d->pageStep);
+        d->offset_accumulated -= int(d->offset_accumulated);
+        if (stepsToScroll == 0)
+            return;
     }
 
     if (d->invertedControls)
@@ -725,12 +723,10 @@ void QAbstractSlider::wheelEvent(QWheelEvent * e)
     d->position = d->overflowSafeAdd(stepsToScroll); // value will be updated by triggerAction()
     triggerAction(SliderMove);
 
-    if (prevValue == d->value) {
+    if (prevValue == d->value)
         d->offset_accumulated = 0;
-    } else {
-        d->offset_accumulated -= int(d->offset_accumulated);
+    else
         e->accept();
-    }
 }
 #endif
 #ifdef QT_KEYPAD_NAVIGATION