Fix: Abstract slider does not understand wheel events properly

A wheel event contain delta values that describe the rotation
angle the wheel was rotated (in 1/8 of a degree).
For some mouse devices (thinking of mac mighty mouse/trackpad)
the resolution is better than the standard 15 degrees. The Qt
docs describe how to deal with this. But abstract scrollbar does
did follow this recipe, but it does now with this patch.

Reb-By: prasanth

1 files changed, 15 insertions, 5 deletions

diff --git a/src/gui/kernel/qapplication_mac.mm b/src/gui/kernel/qapplication_mac.mm
index c294e6221c..a95ae9db1b 100644
--- a/src/gui/kernel/qapplication_mac.mm
+++ b/src/gui/kernel/qapplication_mac.mm
@@ -1686,13 +1686,15 @@ 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;
+            wheel_deltaX = mdelt * scrollFactor;
+            mdelt = 0;
             GetEventParameter(event, kEventParamMouseWheelSmoothVerticalDelta, typeSInt32, 0,
                               sizeof(mdelt), 0, &mdelt);
-            wheel_deltaY = mdelt;
+            wheel_deltaY = mdelt * scrollFactor;
             GetEventParameter(event, kEventParamEventRef, typeEventRef, 0,
                               sizeof(compatibilityEvent), 0, &compatibilityEvent);
         } else if (ekind == kEventMouseWheelMoved) {
@@ -1704,10 +1706,14 @@ QApplicationPrivate::globalEventProcessor(EventHandlerCallRef er, EventRef event
                 EventMouseWheelAxis axis;
                 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:
+                int scrollFactor = 120 * qMin(5, qAbs(mdelt));
                 if (axis == kEventMouseWheelAxisX)
-                    wheel_deltaX = mdelt * 120;
+                    wheel_deltaX = mdelt * scrollFactor;
                 else
-                    wheel_deltaY = mdelt * 120;
+                    wheel_deltaY = mdelt * scrollFactor;
             }
         }
 
@@ -2660,7 +2666,11 @@ int QApplication::keyboardInputInterval()
 
 void QApplication::setWheelScrollLines(int n)
 {
-    QApplicationPrivate::wheel_scroll_lines = 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;
 }
 
 int QApplication::wheelScrollLines()