Fix a problem with external views where the sky lighting was calculated

in reverse.

src/Main/viewer.hxx

@@ -68,6 +68,7 @@ protected:
     // the current view offset angle from forward (rotated about the
     // view_up vector)
     double view_offset;
+    bool reverse_view_offset;
 
     // the goal view offset angle  (used for smooth view changes)
     double goal_view_offset;
@@ -142,6 +143,9 @@ public:
 	set_dirty();
 	goal_view_offset = a;
     }
+    inline void set_reverse_view_offset( bool val ) {
+	reverse_view_offset = val;
+    }
     inline void set_geod_view_pos( double lon, double lat, double alt ) {
 	// data should be in radians and meters asl
 	set_dirty();
@@ -168,6 +172,7 @@ public:
     inline double get_fov() const { return fov; }
     inline double get_win_ratio() const { return win_ratio; }
     inline double get_view_offset() const { return view_offset; }
+    inline bool get_reverse_view_offset() const { return reverse_view_offset; }
     inline double get_goal_view_offset() const { return goal_view_offset; }
     inline double *get_geod_view_pos() { return geod_view_pos; }
     inline float *get_pilot_offset() { return pilot_offset; }

src/Main/viewer_lookat.cxx

@@ -45,6 +45,7 @@
 // Constructor
 FGViewerLookAt::FGViewerLookAt( void )
 {
+    set_reverse_view_offset(true);
 }
 
 

src/Main/viewer_rph.cxx

@@ -46,6 +46,7 @@
 // Constructor
 FGViewerRPH::FGViewerRPH( void )
 {
+    set_reverse_view_offset(false);
 #ifndef USE_FAST_VIEWROT
     // This never changes -- NHV
     LARC_TO_SSG[0][0] = 0.0; 

src/Time/light.cxx

@@ -169,6 +169,9 @@ void fgLIGHT::UpdateAdjFog( void ) {
     // direction to the sun
     rotation = -(sun_rotation + FG_PI) 
 	- (f->get_Psi() - globals->get_current_view()->get_view_offset());
+    if ( globals->get_current_view()->get_reverse_view_offset() ) {
+	rotation += FG_PI;
+    }
     while ( rotation < 0 ) {
 	rotation += FG_2PI;
     }