macOS expose scroll invertion in event

applied patch from #18358, thanks for the patch Andy

include/wx/event.h

@@ -1801,6 +1801,10 @@ public:
     // should occur for each delta.
     int GetWheelDelta() const { return m_wheelDelta; }
 
+    // On Mac, has the user selected "Natural" scrolling in their System
+    // Preferences? Currently false on all other OS's.
+    bool IsWheelInverted() const { return m_wheelInverted; }
+
     // Gets the axis the wheel operation concerns; wxMOUSE_WHEEL_VERTICAL
     // (most common case) or wxMOUSE_WHEEL_HORIZONTAL (for horizontal scrolling
     // using e.g. a trackpad).
@@ -1834,6 +1838,7 @@ public:
     wxMouseWheelAxis m_wheelAxis;
     int           m_wheelRotation;
     int           m_wheelDelta;
+    bool          m_wheelInverted;
     int           m_linesPerAction;
     int           m_columnsPerAction;
     float         m_magnification;

interface/wx/event.h

@@ -2795,6 +2795,22 @@ public:
     */
     int GetWheelDelta() const;
 
+    /**
+        On Mac, has the user selected "Natural" scrolling in their System
+        Preferences? Currently false on all other OS's.
+
+        "Natural" scrolling means that content scrolling happens in the
+        opposite direction, and if you are indeed scrolling content then
+        you don't need to use this function because macOS has already
+        inverted the scroll direction.
+        But there can be special situations where you want the mouse wheel
+        action to work always in the same direction and in that case you
+        will need this function.
+
+        @since 3.1.3
+    */
+    bool IsWheelInverted() const;
+
     /**
         Get wheel rotation, positive or negative indicates direction of rotation.
 

samples/scroll/scroll.cpp

@@ -708,9 +708,10 @@ void MyCanvas::OnMouseWheel( wxMouseEvent &event )
     int x,y;
     CalcUnscrolledPosition( pt.x, pt.y, &x, &y );
     wxLogMessage( "Mouse wheel event at: %d %d, scrolled: %d %d\n"
-                  "Rotation: %d, delta = %d",
+                  "Rotation: %d, delta: %d, inverted: %d",
                   pt.x, pt.y, x, y,
-                  event.GetWheelRotation(), event.GetWheelDelta() );
+                  event.GetWheelRotation(), event.GetWheelDelta(),
+                  event.IsWheelInverted() );
 
     event.Skip();
 }

src/common/event.cpp

@@ -577,6 +577,7 @@ wxMouseEvent::wxMouseEvent(wxEventType commandType)
     m_wheelAxis = wxMOUSE_WHEEL_VERTICAL;
     m_wheelRotation = 0;
     m_wheelDelta = 0;
+    m_wheelInverted = false;
     m_linesPerAction = 0;
     m_columnsPerAction = 0;
     m_magnification = 0.0f;
@@ -601,6 +602,7 @@ void wxMouseEvent::Assign(const wxMouseEvent& event)
 
     m_wheelRotation = event.m_wheelRotation;
     m_wheelDelta = event.m_wheelDelta;
+    m_wheelInverted = event.m_wheelInverted;
     m_linesPerAction = event.m_linesPerAction;
     m_columnsPerAction = event.m_columnsPerAction;
     m_wheelAxis = event.m_wheelAxis;

src/osx/cocoa/window.mm

@@ -719,9 +719,10 @@ void wxWidgetCocoaImpl::SetupMouseEvent( wxMouseEvent &wxevent , NSEvent * nsEve
             }
             
             wxevent.m_wheelDelta = 10;
+            wxevent.m_wheelInverted = [nsEvent isDirectionInvertedFromDevice];
             wxevent.m_linesPerAction = 1;
             wxevent.m_columnsPerAction = 1;
-                
+
             if ( fabs(deltaX) > fabs(deltaY) )
             {
                 // wx conventions for horizontal are inverted from vertical (originating from native msw behavior)