Add almost completely useless flip() method

panda/src/collide/collisionPlane.I

@@ -99,3 +99,13 @@ INLINE const Planef &CollisionPlane::
 get_plane() const {
   return _plane;
 }
+
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionPlane::flip
+//       Access: Published
+//  Description: Convenience method to flip the plane in-place.
+////////////////////////////////////////////////////////////////////
+INLINE void CollisionPlane::
+flip() {
+  _plane.flip();
+}

panda/src/collide/collisionPlane.h

@@ -55,6 +55,8 @@ PUBLISHED:
   INLINE void set_plane(const Planef &plane);
   INLINE const Planef &get_plane() const;
 
+  INLINE void flip();
+
 protected:
   virtual PT(BoundingVolume) compute_internal_bounds() const;
 

panda/src/mathutil/plane_src.I

@@ -66,7 +66,7 @@ FLOATNAME(Plane)(const FLOATNAME(LPoint3) &a, const FLOATNAME(LPoint3) &b,
 //               a point within the plane.
 ////////////////////////////////////////////////////////////////////
 INLINE_MATHUTIL FLOATNAME(Plane)::
-FLOATNAME(Plane)(const FLOATNAME(LVector3) &normal, 
+FLOATNAME(Plane)(const FLOATNAME(LVector3) &normal,
                  const FLOATNAME(LPoint3) &point) {
   FLOATNAME(LVector3) p = ::normalize(normal);
 
@@ -177,6 +177,20 @@ project(const FLOATNAME(LPoint3) &point) const {
   return point - get_normal() * dist_to_plane(point);
 }
 
+////////////////////////////////////////////////////////////////////
+//     Function: Plane::flip
+//       Access: Published
+//  Description: Convenience method that flips the plane in-place.
+//               This is done by simply flipping the normal vector.
+////////////////////////////////////////////////////////////////////
+INLINE_MATHUTIL void FLOATNAME(Plane)::
+flip() {
+  _v.v._0 = -_v.v._0;
+  _v.v._1 = -_v.v._1;
+  _v.v._2 = -_v.v._2;
+  // We don't flip D, that would make the plane flip over the origin.
+}
+
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::intersects_line
 //       Access: Published

panda/src/mathutil/plane_src.h

@@ -21,7 +21,7 @@ class EXPCL_PANDA_MATHUTIL FLOATNAME(Plane) : public FLOATNAME(LVecBase4) {
 PUBLISHED:
   INLINE_MATHUTIL FLOATNAME(Plane)();
   INLINE_MATHUTIL FLOATNAME(Plane)(const FLOATNAME(LVecBase4) &copy);
-  INLINE_MATHUTIL FLOATNAME(Plane)(const FLOATNAME(LPoint3) &a, 
+  INLINE_MATHUTIL FLOATNAME(Plane)(const FLOATNAME(LPoint3) &a,
                                    const FLOATNAME(LPoint3) &b,
                                    const FLOATNAME(LPoint3) &c);
   INLINE_MATHUTIL FLOATNAME(Plane)(const FLOATNAME(LVector3) &normal,
@@ -42,7 +42,7 @@ PUBLISHED:
 
   INLINE_MATHUTIL FLOATTYPE dist_to_plane(const FLOATNAME(LPoint3) &point) const;
   INLINE_MATHUTIL FLOATNAME(LPoint3) project(const FLOATNAME(LPoint3) &point) const;
-
+  INLINE_MATHUTIL void flip();
 
   INLINE_MATHUTIL bool intersects_line(FLOATNAME(LPoint3) &intersection_point,
                                        const FLOATNAME(LPoint3) &p1,