Mac: scroll speed does not match native applications

It turns out that we limit wheel scrolling on mac to an
upper limit per event to one page. This behaviour is a bit
strange in the first place, and on mac, it is just wrong.
Besides, even when this limitation is removed, we still scroll
a bit slower that native. The 'problem' is to come up with a
good conversion from pixel scrolling to line based
scrolling (Qt does not really have an API for pixel scrolling).
But we up the speed a bit to make it perform more similar to
xcode.

Rev-by: msorvig

3 files changed, 22 insertions, 8 deletions

diff --git a/src/gui/kernel/qapplication_mac.mm b/src/gui/kernel/qapplication_mac.mm
index c7d0e48..28072fc 100644
--- a/src/gui/kernel/qapplication_mac.mm
+++ b/src/gui/kernel/qapplication_mac.mm
@@ -1759,14 +1759,19 @@ 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'.
+            // Since delta is delivered as pixels rather than degrees, we need to
+            // convert from pixels to degrees in a sensible manner.
+            // It looks like 1/4 degrees per pixel behaves most native.
+            // (NB: Qt expects the unit for delta to be 8 per degree):
+            const int pixelsToDegrees = 2;
             SInt32 mdelt = 0;
             GetEventParameter(event, kEventParamMouseWheelSmoothHorizontalDelta, typeSInt32, 0,
                               sizeof(mdelt), 0, &mdelt);
-            wheel_deltaX = mdelt;
+            wheel_deltaX = mdelt * pixelsToDegrees;
             mdelt = 0;
             GetEventParameter(event, kEventParamMouseWheelSmoothVerticalDelta, typeSInt32, 0,
                               sizeof(mdelt), 0, &mdelt);
-            wheel_deltaY = mdelt;
+            wheel_deltaY = mdelt * pixelsToDegrees;
             GetEventParameter(event, kEventParamEventRef, typeEventRef, 0,
                               sizeof(compatibilityEvent), 0, &compatibilityEvent);
         } else if (ekind == kEventMouseWheelMoved) {
diff --git a/src/gui/kernel/qcocoaview_mac.mm b/src/gui/kernel/qcocoaview_mac.mm
index f7cb21f..4f71681 100644
--- a/src/gui/kernel/qcocoaview_mac.mm
+++ b/src/gui/kernel/qcocoaview_mac.mm
@@ -480,7 +480,7 @@ static int qCocoaViewCount = 0;
         return;
 
     if (QApplicationPrivate::graphicsSystem() != 0) {
-        if (QWidgetBackingStore *bs = qwidgetprivate->maybeBackingStore()) {
+        if (qwidgetprivate->maybeBackingStore()) {
             // Drawing is handled on the window level
             // See qcocoasharedwindowmethods_mac_p.h
             if (!qwidget->testAttribute(Qt::WA_PaintOnScreen))
@@ -819,11 +819,12 @@ static int qCocoaViewCount = 0;
         // 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:
-        deltaX = [theEvent deviceDeltaX];
-        deltaY = [theEvent deviceDeltaY];
-        deltaZ = [theEvent deviceDeltaZ];
+        // It looks like 1/4 degrees per pixel behaves most native.
+        // (NB: Qt expects the unit for delta to be 8 per degree):
+        const int pixelsToDegrees = 2; // 8 * 1/4
+        deltaX = [theEvent deviceDeltaX] * pixelsToDegrees;
+        deltaY = [theEvent deviceDeltaY] * pixelsToDegrees;
+        deltaZ = [theEvent deviceDeltaZ] * pixelsToDegrees;
     } else {
         // carbonEventKind == kEventMouseWheelMoved
         // Remove acceleration, and use either -120 or 120 as delta:
diff --git a/src/gui/widgets/qabstractslider.cpp b/src/gui/widgets/qabstractslider.cpp
index 2888490..522d472 100644
--- a/src/gui/widgets/qabstractslider.cpp
+++ b/src/gui/widgets/qabstractslider.cpp
@@ -712,7 +712,15 @@ bool QAbstractSliderPrivate::scrollByDelta(Qt::Orientation orientation, Qt::Keyb
             offset_accumulated = 0;
 
         offset_accumulated += stepsToScrollF;
+#ifndef Q_WS_MAC
+        // Dont't scroll more than one page in any case:
         stepsToScroll = qBound(-pageStep, int(offset_accumulated), pageStep);
+#else
+        // Native UI-elements on Mac can scroll hundreds of lines at a time as
+        // a result of acceleration. So keep the same behaviour in Qt, and
+        // dont restrict stepsToScroll to certain maximum (pageStep): 
+        stepsToScroll = int(offset_accumulated);
+#endif
         offset_accumulated -= int(offset_accumulated);
         if (stepsToScroll == 0)
             return false;