Make the knob mouse-wheel direction configurable.

Add a global setting to control the mouse-wheel direction of the knob; a future commit will expose this in the FG GUI.

simgear/scene/model/SGPickAnimation.cxx

@@ -361,6 +361,8 @@ static void readOptionalBindingList(const SGPropertyNode* aNode, SGPropertyNode*
     
 }
 
+static bool static_knobMouseWheelAlternateDirection = false;
+
 class SGKnobAnimation::KnobPickCallback : public SGPickCallback {
 public:
     KnobPickCallback(const SGPropertyNode* configNode,
@@ -401,10 +403,13 @@ public:
             button = 1;
         }
         
+        int increaseMouseWheel = static_knobMouseWheelAlternateDirection ? 3 : 4;
+        int decreaseMouseWheel = static_knobMouseWheelAlternateDirection ? 4 : 3;
+            
         _direction = DIRECTION_NONE;
-        if ((button == 0) || (button == 4)) {
+        if ((button == 0) || (button == increaseMouseWheel)) {
             _direction = DIRECTION_CLOCKWISE;
-        } else if ((button == 1) || (button == 3)) {
+        } else if ((button == 1) || (button == decreaseMouseWheel)) {
             _direction = DIRECTION_ANTICLOCKWISE;
         } else {
             return false;
@@ -518,3 +523,8 @@ SGKnobAnimation::createAnimationGroup(osg::Group& parent)
     return transform;
 }
 
+void SGKnobAnimation::setAlternateMouseWheelDirection(bool aToggle)
+{
+    static_knobMouseWheelAlternateDirection = aToggle;
+}
+

simgear/scene/model/SGPickAnimation.hxx

@@ -54,6 +54,12 @@ public:
                     SGPropertyNode* modelRoot);
     virtual osg::Group* createAnimationGroup(osg::Group& parent);
 
+    /**
+     * by default mouse wheel up corresponds to increment (CW)
+     * and mouse-wheel down corresponds to decrement (CCW).
+     * Since no one can agree on that, make it a global toggle.
+     */
+    static void setAlternateMouseWheelDirection(bool aToggle);
 private:
     class KnobPickCallback;
     class UpdateCallback;