NDOF: minor tweaks based on feedback.

- invert Y axis when swap YZ is enabled.
- allow rotating when not in ortho mode.

source/blender/editors/space_view3d/view3d_edit.c

@@ -1548,7 +1548,7 @@ static int ndof_orbit_zoom_invoke(bContext *C, wmOperator *op, const wmEvent *ev
 		if (ndof->progress == P_FINISHING) {
 			/* pass */
 		}
-		else if (RV3D_VIEW_IS_AXIS(rv3d->view)) {
+		else if ((rv3d->persp == RV3D_ORTHO) && RV3D_VIEW_IS_AXIS(rv3d->view)) {
 			/* if we can't rotate, fallback to translate (locked axis views) */
 			const bool has_translate = NDOF_HAS_TRANSLATE;
 			const bool has_zoom = (ndof->tvec[2] != 0.0f) && ED_view3d_offset_lock_check(v3d, rv3d);

source/blender/windowmanager/intern/wm_event_system.c

@@ -2883,14 +2883,11 @@ static void attach_ndof_data(wmEvent *event, const GHOST_TEventNDOFMotionData *g
 	mul_v3_v3fl(data->tvec, &ghost->tx, ts);
 	mul_v3_v3fl(data->rvec, &ghost->rx, rs);
 
-	/**
-	 * \note
-	 * - optionally swap Y/Z.
-	 * - maintain handed-ness? or just do what feels right? not for now.
-	 * - after testing seems best not to apply this to rotation.
-	 */
 	if (U.ndof_flag & NDOF_PAN_YZ_SWAP_AXIS) {
-		SWAP(float, data->tvec[1], data->tvec[2]);
+		float t;
+		t =  data->tvec[1];
+		data->tvec[1] = -data->tvec[2];
+		data->tvec[2] = t;
 	}
 
 	data->dt = ghost->dt;