diff --git a/panda/src/collide/collisionEntry.I b/panda/src/collide/collisionEntry.I
index 45d640cfc2..ec2c7c15b2 100644
--- a/panda/src/collide/collisionEntry.I
+++ b/panda/src/collide/collisionEntry.I
@@ -457,6 +457,21 @@ get_wrt_prev_mat() const {
   return get_wrt_prev_space()->get_mat();
 }
 
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionEntry::get_into_clip_planes
+//       Access: Public
+//  Description: Returns the ClipPlaneAttrib, if any, that is applied
+//               to the into_node_path, or NULL if there is no clip
+//               plane in effect.
+////////////////////////////////////////////////////////////////////
+INLINE const ClipPlaneAttrib *CollisionEntry::
+get_into_clip_planes() const {
+  if ((_flags & F_checked_clip_planes) == 0) {
+    ((CollisionEntry *)this)->check_clip_planes();
+  }
+  return _into_clip_planes;
+}
+
 ////////////////////////////////////////////////////////////////////
 //     Function: CollisionEntry::test_intersection
 //       Access: Private
diff --git a/panda/src/collide/collisionEntry.cxx b/panda/src/collide/collisionEntry.cxx
index d7a1582141..e68798d65c 100644
--- a/panda/src/collide/collisionEntry.cxx
+++ b/panda/src/collide/collisionEntry.cxx
@@ -17,6 +17,7 @@
 ////////////////////////////////////////////////////////////////////
 
 #include "collisionEntry.h"
+#include "dcast.h"
 
 TypeHandle CollisionEntry::_type_handle;
 
@@ -33,6 +34,7 @@ CollisionEntry(const CollisionEntry &copy) :
   _into_node(copy._into_node),
   _from_node_path(copy._from_node_path),
   _into_node_path(copy._into_node_path),
+  _into_clip_planes(copy._into_clip_planes),
   _flags(copy._flags),
   _surface_point(copy._surface_point),
   _surface_normal(copy._surface_normal),
@@ -53,6 +55,7 @@ operator = (const CollisionEntry &copy) {
   _into_node = copy._into_node;
   _from_node_path = copy._from_node_path;
   _into_node_path = copy._into_node_path;
+  _into_clip_planes = copy._into_clip_planes;
   _flags = copy._flags;
   _surface_point = copy._surface_point;
   _surface_normal = copy._surface_normal;
@@ -151,3 +154,19 @@ get_all(const NodePath &space, LPoint3f &surface_point,
 
   return true;
 }
+
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionEntry::check_clip_planes
+//       Access: Private
+//  Description: Checks whether the into_node_path has a
+//               ClipPlaneAttrib defined.
+////////////////////////////////////////////////////////////////////
+void CollisionEntry::
+check_clip_planes() {
+  const RenderAttrib *cpa_attrib =
+    _into_node_path.get_net_state()->get_attrib(ClipPlaneAttrib::get_class_type());
+  if (cpa_attrib != (const RenderAttrib *)NULL) {
+    _into_clip_planes = DCAST(ClipPlaneAttrib, cpa_attrib);
+  }
+  _flags |= F_checked_clip_planes;
+}
diff --git a/panda/src/collide/collisionEntry.h b/panda/src/collide/collisionEntry.h
index b0acf92c5e..2e19f7ec6b 100644
--- a/panda/src/collide/collisionEntry.h
+++ b/panda/src/collide/collisionEntry.h
@@ -32,6 +32,7 @@
 #include "pointerTo.h"
 #include "pandaNode.h"
 #include "nodePath.h"
+#include "clipPlaneAttrib.h"
 
 ///////////////////////////////////////////////////////////////////
 //       Class : CollisionEntry
@@ -111,12 +112,12 @@ public:
   INLINE const LMatrix4f &get_inv_wrt_mat() const;
   INLINE const LMatrix4f &get_wrt_prev_mat() const;
 
-
+  INLINE const ClipPlaneAttrib *get_into_clip_planes() const;
 
 private:
   INLINE void test_intersection(CollisionHandler *record, 
                                 const CollisionTraverser *trav) const;
-  void compute_from_surface_normal();
+  void check_clip_planes();
 
   CPT(CollisionSolid) _from;
   CPT(CollisionSolid) _into;
@@ -125,12 +126,14 @@ private:
   PT(PandaNode) _into_node;
   NodePath _from_node_path;
   NodePath _into_node_path;
+  CPT(ClipPlaneAttrib) _into_clip_planes;
 
   enum Flags {
     F_has_surface_point       = 0x0001,
     F_has_surface_normal      = 0x0002,
     F_has_interior_point      = 0x0004,
     F_respect_prev_transform  = 0x0008,
+    F_checked_clip_planes     = 0x0010,
   };
 
   int _flags;
diff --git a/panda/src/collide/collisionNode.cxx b/panda/src/collide/collisionNode.cxx
index 0fda1e0907..fbb256b55c 100644
--- a/panda/src/collide/collisionNode.cxx
+++ b/panda/src/collide/collisionNode.cxx
@@ -207,13 +207,15 @@ cull_callback(CullTraverser *trav, CullTraverserData &data) {
   Solids::iterator si;
   for (si = _solids.begin(); si != _solids.end(); ++si) {
     CollisionSolid *solid = (*si);
-    PandaNode *node = solid->get_viz();
-    CullTraverserData next_data(data, node);
+    PT(PandaNode) node = solid->get_viz(data);
+    if (node != (PandaNode *)NULL) {
+      CullTraverserData next_data(data, node);
 
-    // We don't want to inherit the render state from above for these
-    // guys.
-    next_data._state = RenderState::make_empty();
-    trav->traverse(next_data);
+      // We don't want to inherit the render state from above for these
+      // guys.
+      next_data._state = RenderState::make_empty();
+      trav->traverse(next_data);
+    }
   }
 
   // Determine the previous frame's position, relative to the
@@ -227,13 +229,15 @@ cull_callback(CullTraverser *trav, CullTraverserData &data) {
 
     for (si = _solids.begin(); si != _solids.end(); ++si) {
       CollisionSolid *solid = (*si);
-      PandaNode *node = solid->get_viz();
-      CullTraverserData next_data(data, node);
+      PT(PandaNode) node = solid->get_viz(data);
+      if (node != (PandaNode *)NULL) {
+        CullTraverserData next_data(data, node);
 
-      next_data._render_transform = 
-        next_data._render_transform->compose(transform);
-      next_data._state = get_last_pos_state();
-      trav->traverse(next_data);
+        next_data._render_transform = 
+          next_data._render_transform->compose(transform);
+        next_data._state = get_last_pos_state();
+        trav->traverse(next_data);
+      }
     }
   }
 
diff --git a/panda/src/collide/collisionPolygon.cxx b/panda/src/collide/collisionPolygon.cxx
index 303d33c860..7241dcd8af 100644
--- a/panda/src/collide/collisionPolygon.cxx
+++ b/panda/src/collide/collisionPolygon.cxx
@@ -24,6 +24,7 @@
 #include "collisionSegment.h"
 #include "config_collide.h"
 
+#include "cullTraverserData.h"
 #include "boundingSphere.h"
 #include "pointerToArray.h"
 #include "geomNode.h"
@@ -34,6 +35,7 @@
 #include "bamWriter.h"
 #include "geomPolygon.h"
 #include "transformState.h"
+#include "clipPlaneAttrib.h"
 
 #include <algorithm>
 
@@ -186,6 +188,50 @@ get_collision_origin() const {
   return to_3d(_median);
 }
 
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionPolygon::get_viz
+//       Access: Public, Virtual
+//  Description: Returns a GeomNode that may be rendered to visualize
+//               the CollisionSolid.  This is used during the cull
+//               traversal to render the CollisionNodes that have been
+//               made visible.
+////////////////////////////////////////////////////////////////////
+PT(PandaNode) CollisionPolygon::
+get_viz(const CullTraverserData &data) const {
+  const RenderAttrib *cpa_attrib =
+    data._state->get_attrib(ClipPlaneAttrib::get_class_type());
+  if (cpa_attrib == (const RenderAttrib *)NULL) {
+    // Fortunately, the polygon is not clipped.  This is the normal,
+    // easy case.
+    return CollisionSolid::get_viz(data);
+  }
+
+  // The polygon is clipped.  We need to render it clipped.  We could
+  // just turn on the ClipPlaneAttrib state and render the full
+  // polygon, letting the hardware do the clipping, but we get fancy
+  // and clip it by hand instead, just to prove that our clipping
+  // algorithm works properly.  This does require some more dynamic
+  // work.
+  const ClipPlaneAttrib *cpa = DCAST(ClipPlaneAttrib, cpa_attrib);
+  Points new_points;
+  if (apply_clip_plane(new_points, cpa, data._net_transform)) {
+    // All points are behind the clip plane; just draw the original
+    // polygon.
+    return CollisionSolid::get_viz(data);
+  }
+
+  if (new_points.empty()) {
+    // All points are in front of the clip plane; draw nothing.
+    return NULL;
+  }
+
+  // Draw the clipped polygon.
+  PT(GeomNode) geom_node = new GeomNode("viz");
+  draw_polygon(geom_node, new_points);
+
+  return geom_node.p();
+}
+
 ////////////////////////////////////////////////////////////////////
 //     Function: CollisionPolygon::output
 //       Access: Public, Virtual
@@ -343,56 +389,37 @@ test_intersection_from_sphere(const CollisionEntry &entry) const {
 
   LPoint2f p = to_2d(plane_point);
 
-  // Now we have found a point on the polygon's plane that corresponds
-  // to the point tangent to our collision sphere where it first
-  // touches the plane.  We want to decide whether the sphere itself
-  // will intersect the polygon.  We can approximate this by testing
-  // whether a circle of the given radius centered around this tangent
-  // point, in the plane of the polygon, would intersect.
+  const ClipPlaneAttrib *cpa = entry.get_into_clip_planes();
+  if (cpa != (ClipPlaneAttrib *)NULL) {
+    // We have a clip plane; apply it.
+    Points new_points;
+    if (apply_clip_plane(new_points, cpa, entry.get_into_node_path().get_net_transform())) {
+      // All points are behind the clip plane; just do the default
+      // test.
+      if (!circle_is_inside(p, from_radius, _points, _median)) {
+        return NULL;
+      }
 
-  // But even this approximate test is too difficult.  To approximate
-  // the approximation, we'll test two points: (1) the center itself.
-  // If this is inside the polygon, then certainly the circle
-  // intersects the polygon, and the sphere collides.  (2) a point on
-  // the outside of the circle, nearest to the center of the polygon.
-  // If _this_ point is inside the polygon, then again the circle, and
-  // hence the sphere, intersects.  If neither point is inside the
-  // polygon, chances are reasonably good the sphere doesn't intersect
-  // the polygon after all.
+    } else if (new_points.empty()) {
+      // The polygon is completely clipped.
+      return NULL;
 
-  if (is_inside(p)) {
-    // The circle's center is inside the polygon; we have a collision!
+    } else {
+      // Test against the clipped polygon.
+      LPoint2f new_median = new_points[0];
+      for (int n = 1; n < (int)new_points.size(); n++) {
+        new_median += new_points[n];
+      }
+      new_median /= new_points.size();
+      if (!circle_is_inside(p, from_radius, new_points, new_median)) {
+        return NULL;
+      }
+    }
 
   } else {
-
-    if (from_radius > 0.0f) {
-      // Now find the point on the rim of the circle nearest the
-      // polygon's center.
-
-      // First, get a vector from the center of the circle to the center
-      // of the polygon.
-      LVector2f rim = _median - p;
-      float rim_length = length(rim);
-
-      if (rim_length <= from_radius) {
-        // Here's a surprise: the center of the polygon is within the
-        // circle!  Since the center is guaranteed to be interior to the
-        // polygon (the polygon is convex), it follows that the circle
-        // intersects the polygon.
-
-      } else {
-        // Now scale this vector to length radius, and get the new point.
-        rim = (rim * from_radius / rim_length) + p;
-
-        // Is the new point within the polygon?
-        if (is_inside(rim)) {
-          // It sure is!  The circle intersects!
-
-        } else {
-          // No intersection.
-          return NULL;
-        }
-      }
+    // No clip plane is in effect.  Do the default test.
+    if (!circle_is_inside(p, from_radius, _points, _median)) {
+      return NULL;
     }
   }
 
@@ -451,9 +478,25 @@ test_intersection_from_ray(const CollisionEntry &entry) const {
   }
 
   LPoint3f plane_point = from_origin + t * from_direction;
-  if (!is_inside(to_2d(plane_point))) {
-    // Outside the polygon's perimeter.
-    return NULL;
+  LPoint2f p = to_2d(plane_point);
+
+  const ClipPlaneAttrib *cpa = entry.get_into_clip_planes();
+  if (cpa != (ClipPlaneAttrib *)NULL) {
+    // We have a clip plane; apply it.
+    Points new_points;
+    apply_clip_plane(new_points, cpa, entry.get_into_node_path().get_net_transform());
+    if (new_points.size() < 3) {
+      return NULL;
+    }
+    if (!point_is_inside(p, new_points)) {
+      return NULL;
+    }
+
+  } else {
+    // No clip plane is in effect.  Do the default test.
+    if (!point_is_inside(p, _points)) {
+      return NULL;
+    }
   }
 
   if (collide_cat.is_debug()) {
@@ -504,9 +547,25 @@ test_intersection_from_segment(const CollisionEntry &entry) const {
   }
 
   LPoint3f plane_point = from_a + t * from_direction;
-  if (!is_inside(to_2d(plane_point))) {
-    // Outside the polygon's perimeter.
-    return NULL;
+  LPoint2f p = to_2d(plane_point);
+
+  const ClipPlaneAttrib *cpa = entry.get_into_clip_planes();
+  if (cpa != (ClipPlaneAttrib *)NULL) {
+    // We have a clip plane; apply it.
+    Points new_points;
+    apply_clip_plane(new_points, cpa, entry.get_into_node_path().get_net_transform());
+    if (new_points.size() < 3) {
+      return NULL;
+    }
+    if (!point_is_inside(p, new_points)) {
+      return NULL;
+    }
+
+  } else {
+    // No clip plane is in effect.  Do the default test.
+    if (!point_is_inside(p, _points)) {
+      return NULL;
+    }
   }
 
   if (collide_cat.is_debug()) {
@@ -534,8 +593,19 @@ fill_viz_geom() {
     collide_cat.debug()
       << "Recomputing viz for " << *this << "\n";
   }
+  draw_polygon(_viz_geom, _points);
+}
 
-  if (_points.size() < 3) {
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionPolygon::draw_polygon
+//       Access: Private
+//  Description: Fills up the indicated GeomNode with the Geoms to
+//               draw the polygon indicated with the given set of 2-d
+//               points.
+////////////////////////////////////////////////////////////////////
+void CollisionPolygon::
+draw_polygon(GeomNode *geom_node, const CollisionPolygon::Points &points) const {
+  if (points.size() < 3) {
     if (collide_cat.is_debug()) {
       collide_cat.debug()
         << "(Degenerate poly, ignoring.)\n";
@@ -545,7 +615,7 @@ fill_viz_geom() {
 
   PTA_Vertexf verts;
   Points::const_iterator pi;
-  for (pi = _points.begin(); pi != _points.end(); ++pi) {
+  for (pi = points.begin(); pi != points.end(); ++pi) {
     verts.push_back(to_3d(*pi));
   }
   if (_reversed) {
@@ -553,42 +623,109 @@ fill_viz_geom() {
   }
 
   PTA_int lengths;
-  lengths.push_back(_points.size());
+  lengths.push_back(points.size());
 
   GeomPolygon *polygon = new GeomPolygon;
   polygon->set_coords(verts);
   polygon->set_num_prims(1);
   polygon->set_lengths(lengths);
 
-  _viz_geom->add_geom(polygon, get_solid_viz_state());
-  _viz_geom->add_geom(polygon, get_wireframe_viz_state());
+  geom_node->add_geom(polygon, ((CollisionPolygon *)this)->get_solid_viz_state());
+  geom_node->add_geom(polygon, ((CollisionPolygon *)this)->get_wireframe_viz_state());
 }
 
+
 ////////////////////////////////////////////////////////////////////
-//     Function: CollisionPolygon::is_inside
+//     Function: CollisionPolygon::point_is_inside
 //       Access: Private
-//  Description:
+//  Description: Returns true if the indicated point is within the
+//               polygon's 2-d space, false otherwise.
 ////////////////////////////////////////////////////////////////////
 bool CollisionPolygon::
-is_inside(const LPoint2f &p) const {
+point_is_inside(const LPoint2f &p, const CollisionPolygon::Points &points) const {
   // We insist that the polygon be convex.  This makes things a bit simpler.
 
   // In the case of a convex polygon, defined with points in counterclockwise
   // order, a point is interior to the polygon iff the point is not right of
   // each of the edges.
-
-  for (int i = 0; i < (int)_points.size() - 1; i++) {
-    if (is_right(p - _points[i], _points[i+1] - _points[i])) {
+  for (int i = 0; i < (int)points.size() - 1; i++) {
+    if (is_right(p - points[i], points[i+1] - points[i])) {
       return false;
     }
   }
-  if (is_right(p - _points[_points.size() - 1],
-               _points[0] - _points[_points.size() - 1])) {
+  if (is_right(p - points[points.size() - 1],
+               points[0] - points[points.size() - 1])) {
     return false;
   }
 
   return true;
+}
 
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionPolygon::circle_is_inside
+//       Access: Private
+//  Description: Returns true if the circle with the indicated center
+//               and radius intersects the polygon in its 2-d space,
+//               false otherwise.
+////////////////////////////////////////////////////////////////////
+bool CollisionPolygon::
+circle_is_inside(const LPoint2f &center, float radius,
+                 const CollisionPolygon::Points &points,
+                 const LPoint2f &median) const {
+  // Now we have found a point on the polygon's plane that corresponds
+  // to the point tangent to our collision sphere where it first
+  // touches the plane.  We want to decide whether the sphere itself
+  // will intersect the polygon.  We can approximate this by testing
+  // whether a circle of the given radius centered around this tangent
+  // point, in the plane of the polygon, would intersect.
+
+  // But even this approximate test is too difficult.  To approximate
+  // the approximation, we'll test two points: (1) the center itself.
+  // If this is inside the polygon, then certainly the circle
+  // intersects the polygon, and the sphere collides.  (2) a point on
+  // the outside of the circle, nearest to the center of the polygon.
+  // If _this_ point is inside the polygon, then again the circle, and
+  // hence the sphere, intersects.  If neither point is inside the
+  // polygon, chances are reasonably good the sphere doesn't intersect
+  // the polygon after all.
+
+  if (point_is_inside(center, points)) {
+    // The circle's center is inside the polygon; we have a collision!
+
+  } else {
+
+    if (radius > 0.0f) {
+      // Now find the point on the rim of the circle nearest the
+      // polygon's center.
+
+      // First, get a vector from the center of the circle to the center
+      // of the polygon.
+      LVector2f rim = median - center;
+      float rim_length = length(rim);
+
+      if (rim_length <= radius) {
+        // Here's a surprise: the center of the polygon is within the
+        // circle!  Since the center is guaranteed to be interior to the
+        // polygon (the polygon is convex), it follows that the circle
+        // intersects the polygon.
+
+      } else {
+        // Now scale this vector to length radius, and get the new point.
+        rim = (rim * radius / rim_length) + center;
+
+        // Is the new point within the polygon?
+        if (point_is_inside(rim, points)) {
+          // It sure is!  The circle intersects!
+
+        } else {
+          // No intersection.
+          return false;
+        }
+      }
+    }
+  }
+  
+  return true;
 }
 
 ////////////////////////////////////////////////////////////////////
@@ -776,7 +913,7 @@ setup_points(const LPoint3f *begin, const LPoint3f *end) {
 //               in the polygon's 2-d definition space.
 ////////////////////////////////////////////////////////////////////
 LPoint2f CollisionPolygon::
-to_2d(const LPoint3f &point3d) const {
+to_2d(const LVecBase3f &point3d) const {
   nassertr(!point3d.is_nan(), LPoint2f(0.0f, 0.0f));
 
   // Project the point of intersection with the plane onto the
@@ -804,7 +941,7 @@ to_2d(const LPoint3f &point3d) const {
 //               definition space back into 3-d coordinates.
 ////////////////////////////////////////////////////////////////////
 LPoint3f CollisionPolygon::
-to_3d(const LPoint2f &point2d) const {
+to_3d(const LVecBase2f &point2d) const {
   nassertr(!point2d.is_nan(), LPoint3f(0.0f, 0.0f, 0.0f));
 
   LVector3f normal = get_normal();
@@ -832,6 +969,140 @@ to_3d(const LPoint2f &point2d) const {
   return LPoint3f(0.0f, 0.0f, 0.0f);
 }
 
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionPolygon::clip_polygon
+//       Access: Private
+//  Description: Clips the source_points of the polygon by the
+//               indicated clipping plane, and modifies new_points to
+//               reflect the new set of clipped points.
+//
+//               The return value is true if the set of points is
+//               unmodified (all points are behind the clip plane), or
+//               false otherwise.
+////////////////////////////////////////////////////////////////////
+bool CollisionPolygon::
+clip_polygon(CollisionPolygon::Points &new_points, 
+             const CollisionPolygon::Points &source_points,
+             const Planef &plane) const {
+  new_points.clear();
+  if (source_points.empty()) {
+    return true;
+  }
+
+  LPoint3f from3d;
+  LVector3f delta3d;
+  if (!plane.intersects_plane(from3d, delta3d, get_plane())) {
+    // The clipping plane is parallel to the polygon.  The polygon is
+    // either all in or all out.
+    if (plane.dist_to_plane(get_plane().get_point()) < 0.0) {
+      // A point within the polygon is behind the clipping plane: the
+      // polygon is all in.
+      new_points = source_points;
+      return true;
+    }
+    return false;
+  }
+
+  // Project the line of intersection into the 2-d plane.  Now we have
+  // a 2-d clipping line.
+  LPoint2f from2d = to_2d(from3d);
+  LVector2f delta2d = to_2d(delta3d);
+  if (_reversed) {
+    delta2d = -delta2d;
+  }
+
+  float a = -delta2d[1];
+  float b = delta2d[0];
+  float c = from2d[0] * delta2d[1] - from2d[1] * delta2d[0];
+
+  // Now walk through the points.  Any point on the left of our line
+  // gets removed, and the line segment clipped at the point of
+  // intersection.
+
+  // We might increase the number of vertices by as many as 1, if the
+  // plane clips off exactly one corner.  (We might also decrease the
+  // number of vertices, or keep them the same number.)
+  new_points.reserve(source_points.size() + 1);
+
+  LPoint2f last_point = source_points.back();
+  bool last_is_in = !is_right(last_point - from2d, delta2d);
+  bool all_in = last_is_in;
+  Points::const_iterator pi;
+  for (pi = source_points.begin(); pi != source_points.end(); ++pi) {
+    const LPoint2f &this_point = (*pi);
+    bool this_is_in = !is_right(this_point - from2d, delta2d);
+
+    if (this_is_in != last_is_in) {
+      // We have just crossed over the clipping line.  Find the point
+      // of intersection.
+      LVector2f d = this_point - last_point;
+      float t = -(a * last_point[0] + b * last_point[1] + c) / (a * d[0] + b * d[1]);
+      LPoint2f p = last_point + t * d;
+
+      new_points.push_back(p);
+      last_is_in = this_is_in;
+    } 
+
+    if (this_is_in) {
+      // We are behind the clipping line.  Keep the point.
+      new_points.push_back(this_point);
+    } else {
+      all_in = false;
+    }
+
+    last_point = this_point;
+  }
+
+  return all_in;
+}
+
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionPolygon::apply_clip_plane
+//       Access: Private
+//  Description: Clips the polygon by all of the clip planes named in
+//               the clip plane attribute and fills new_points up with
+//               the resulting points.
+//
+//               The return value is true if the set of points is
+//               unmodified (all points are behind all the clip
+//               planes), or false otherwise.
+////////////////////////////////////////////////////////////////////
+bool CollisionPolygon::
+apply_clip_plane(CollisionPolygon::Points &new_points, 
+                 const ClipPlaneAttrib *cpa,
+                 const TransformState *net_transform) const {
+  bool all_in = true;
+
+  int num_planes = cpa->get_num_planes();
+  if (num_planes > 0) {
+    PlaneNode *plane_node = cpa->get_plane(0);
+    NodePath plane_path(plane_node);
+    CPT(TransformState) new_transform = 
+      net_transform->invert_compose(plane_path.get_net_transform());
+    
+    Planef plane = plane_node->get_plane() * new_transform->get_mat();
+    if (!clip_polygon(new_points, _points, plane)) {
+      all_in = false;
+    }
+
+    for (int i = 1; i < num_planes; i++) {
+      PlaneNode *plane_node = cpa->get_plane(i);
+      NodePath plane_path(plane_node);
+      CPT(TransformState) new_transform = 
+        net_transform->invert_compose(plane_path.get_net_transform());
+      
+      Planef plane = plane_node->get_plane() * new_transform->get_mat();
+      Points last_points;
+      last_points.swap(new_points);
+      if (!clip_polygon(new_points, last_points, plane)) {
+        all_in = false;
+      }
+    }
+  }
+
+  return all_in;
+}
+
 ////////////////////////////////////////////////////////////////////
 //     Function: CollisionPolygon::write_datagram
 //       Access: Public
diff --git a/panda/src/collide/collisionPolygon.h b/panda/src/collide/collisionPolygon.h
index 160a82e4d0..71b9a9d127 100644
--- a/panda/src/collide/collisionPolygon.h
+++ b/panda/src/collide/collisionPolygon.h
@@ -22,9 +22,12 @@
 #include "pandabase.h"
 
 #include "collisionPlane.h"
+#include "clipPlaneAttrib.h"
 
 #include "vector_LPoint2f.h"
 
+class GeomNode;
+
 ///////////////////////////////////////////////////////////////////
 //       Class : CollisionPolygon
 // Description :
@@ -55,6 +58,8 @@ public:
   virtual void xform(const LMatrix4f &mat);
   virtual LPoint3f get_collision_origin() const;
 
+  virtual PT(PandaNode) get_viz(const CullTraverserData &data) const;
+
   virtual void output(ostream &out) const;
   virtual void write(ostream &out, int indent_level = 0) const;
 
@@ -71,15 +76,26 @@ protected:
   virtual void fill_viz_geom();
 
 private:
-  bool is_inside(const LPoint2f &p) const;
+  typedef vector_LPoint2f Points;
+
+  void draw_polygon(GeomNode *geom_node, const Points &points) const;
+
+  bool point_is_inside(const LPoint2f &p, const Points &points) const;
+  bool circle_is_inside(const LPoint2f &center, float radius,
+                        const CollisionPolygon::Points &points,
+                        const LPoint2f &median) const;
   bool is_concave() const;
 
   void setup_points(const LPoint3f *begin, const LPoint3f *end);
-  LPoint2f to_2d(const LPoint3f &point3d) const;
-  LPoint3f to_3d(const LPoint2f &point2d) const;
+  LPoint2f to_2d(const LVecBase3f &point3d) const;
+  LPoint3f to_3d(const LVecBase2f &point2d) const;
+
+  bool clip_polygon(Points &new_points, const Points &source_points,
+                    const Planef &plane) const;
+  bool apply_clip_plane(Points &new_points, const ClipPlaneAttrib *cpa,
+                        const TransformState *net_transform) const;
 
 private:
-  typedef vector_LPoint2f Points;
   Points _points;
   LPoint2f _median;
 
diff --git a/panda/src/collide/collisionSolid.cxx b/panda/src/collide/collisionSolid.cxx
index fceb59e7e0..643db99552 100644
--- a/panda/src/collide/collisionSolid.cxx
+++ b/panda/src/collide/collisionSolid.cxx
@@ -86,14 +86,14 @@ test_intersection(const CollisionEntry &) const {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: CollisionSolid::get_viz
-//       Access: Public
+//       Access: Public, Virtual
 //  Description: Returns a GeomNode that may be rendered to visualize
 //               the CollisionSolid.  This is used during the cull
 //               traversal to render the CollisionNodes that have been
 //               made visible.
 ////////////////////////////////////////////////////////////////////
-GeomNode *CollisionSolid::
-get_viz() const {
+PT(PandaNode) CollisionSolid::
+get_viz(const CullTraverserData &) const {
   if (_viz_geom_stale) {
     if (_viz_geom == (GeomNode *)NULL) {
       ((CollisionSolid *)this)->_viz_geom = new GeomNode("viz");
@@ -103,7 +103,7 @@ get_viz() const {
     ((CollisionSolid *)this)->fill_viz_geom();
     ((CollisionSolid *)this)->_viz_geom_stale = false;
   }
-  return _viz_geom;
+  return _viz_geom.p();
 }
 
 ////////////////////////////////////////////////////////////////////
diff --git a/panda/src/collide/collisionSolid.h b/panda/src/collide/collisionSolid.h
index 99f6ccebe1..f5aaa6c830 100644
--- a/panda/src/collide/collisionSolid.h
+++ b/panda/src/collide/collisionSolid.h
@@ -33,6 +33,7 @@ class CollisionEntry;
 class CollisionSphere;
 class GeomNode;
 class CollisionNode;
+class CullTraverserData;
 
 ///////////////////////////////////////////////////////////////////
 //       Class : CollisionSolid
@@ -67,7 +68,7 @@ public:
 
   virtual void xform(const LMatrix4f &mat)=0;
 
-  GeomNode *get_viz() const;
+  virtual PT(PandaNode) get_viz(const CullTraverserData &data) const;
 
 PUBLISHED:
   virtual void output(ostream &out) const;
diff --git a/panda/src/collide/collisionVisualizer.cxx b/panda/src/collide/collisionVisualizer.cxx
index a0f3cc5c50..1b2ebaedce 100644
--- a/panda/src/collide/collisionVisualizer.cxx
+++ b/panda/src/collide/collisionVisualizer.cxx
@@ -124,26 +124,31 @@ cull_callback(CullTraverser *trav, CullTraverserData &data) {
     const VizInfo &viz_info = (*di).second;
 
     CullTraverserData xform_data(data);
-
-    // We don't want to inherit the transform state!  We ignore
+    
+    // We don't want to inherit the transform from above!  We ignore
     // whatever transforms were above the CollisionVisualizer node; it
     // always renders its objects according to their appropriate net
     // transform.
     xform_data._net_transform = TransformState::make_identity();
     xform_data._render_transform = trav->get_render_transform();
-    xform_data.apply_transform_and_state(trav, net_transform,
+    xform_data.apply_transform_and_state(trav, net_transform, 
                                          RenderState::make_empty(),
                                          RenderEffects::make_empty());
 
     // Draw all the collision solids.
     Solids::const_iterator si;
     for (si = viz_info._solids.begin(); si != viz_info._solids.end(); ++si) {
+      // Note that we don't preserve the clip plane attribute from the
+      // collision solid.  We always draw the whole polygon (or
+      // whatever) in the CollisionVisualizer.  This is a deliberate
+      // decision; clipping the polygons may obscure many collision
+      // tests that are being made.
       const CollisionSolid *solid = (*si).first;
       const SolidInfo &solid_info = (*si).second;
-      PandaNode *node = solid->get_viz();
-
+      PT(PandaNode) node = solid->get_viz(xform_data);
+        
       CullTraverserData next_data(xform_data, node);
-
+        
       // We don't want to inherit the render state from above for
       // these guys.  Instead, we choose the state according to
       // whether a collision was detected or not.
@@ -152,22 +157,22 @@ cull_callback(CullTraverser *trav, CullTraverserData &data) {
       } else {
         next_data._state = get_tested_state();
       }
-
+        
       trav->traverse(next_data);
     }
 
     // Now draw all of the detected points.
     if (!viz_info._points.empty()) {
       CPT(RenderState) empty_state = RenderState::make_empty();
-
+        
       PTA_Colorf colors;
       colors.push_back(Colorf(1.0f, 0.0f, 0.0f, 1.0f));
       colors.push_back(Colorf(1.0f, 1.0f, 1.0f, 1.0f));
-
+        
       Points::const_iterator pi;
       for (pi = viz_info._points.begin(); pi != viz_info._points.end(); ++pi) {
         const CollisionPoint &point = (*pi);
-
+          
         // Draw a small red sphere at the surface point, and a smaller
         // white sphere at the interior point.
         {
@@ -179,14 +184,14 @@ cull_callback(CullTraverser *trav, CullTraverserData &data) {
           sphere->set_coords(verts);
           sphere->set_colors(colors, G_PER_PRIM);
           sphere->set_num_prims(1);
-          
+            
           if (point._interior_point != point._surface_point) {
             verts.push_back(point._interior_point);
             verts.push_back(point._interior_point + 
                             LVector3f(0.05f * _viz_scale, 0.0f, 0.0f));
             sphere->set_num_prims(2);
           }
-
+            
           CullableObject *object = 
             new CullableObject(sphere, empty_state, xform_data._render_transform);
           
@@ -212,7 +217,6 @@ cull_callback(CullTraverser *trav, CullTraverserData &data) {
         }
       }
     }
-
   }
 
   // Now carry on to render our child nodes.
@@ -261,7 +265,10 @@ void CollisionVisualizer::
 collision_tested(const CollisionEntry &entry, bool detected) {
   CollisionRecorder::collision_tested(entry, detected);
 
-  VizInfo &viz_info = _data[entry.get_into_node_path().get_net_transform()];
+  NodePath node_path = entry.get_into_node_path();
+  CPT(TransformState) net_transform = node_path.get_net_transform();
+
+  VizInfo &viz_info = _data[net_transform];
   if (detected) {
     viz_info._solids[entry.get_into()]._detected_count++;
 
diff --git a/panda/src/collide/collisionVisualizer.h b/panda/src/collide/collisionVisualizer.h
index ef9e5bcc57..75ee51769b 100644
--- a/panda/src/collide/collisionVisualizer.h
+++ b/panda/src/collide/collisionVisualizer.h
@@ -23,6 +23,7 @@
 #include "pandaNode.h"
 #include "collisionRecorder.h"
 #include "nodePath.h"
+#include "pmap.h"
 
 #ifdef DO_COLLISION_RECORDING
 
@@ -84,7 +85,7 @@ private:
     Points _points;
   };
 
-  typedef map<CPT(TransformState), VizInfo> Data;
+  typedef pmap<CPT(TransformState), VizInfo> Data;
   Data _data;
 
   float _viz_scale;
diff --git a/panda/src/mathutil/Sources.pp b/panda/src/mathutil/Sources.pp
index 82fb5be87d..6c700ca4b3 100644
--- a/panda/src/mathutil/Sources.pp
+++ b/panda/src/mathutil/Sources.pp
@@ -51,6 +51,7 @@
   #define TARGET test_mathutil
   #define LOCAL_LIBS \
     mathutil
+  #define OTHER_LIBS $[OTHER_LIBS] pystub
 
   #define SOURCES \
     test_mathutil.cxx
diff --git a/panda/src/mathutil/plane.h b/panda/src/mathutil/plane.h
index 87e1520bad..71a3465bea 100644
--- a/panda/src/mathutil/plane.h
+++ b/panda/src/mathutil/plane.h
@@ -19,12 +19,12 @@
 #ifndef PLANE_H
 #define PLANE_H
 
-#include <pandabase.h>
+#include "pandabase.h"
 
-#include <luse.h>
-#include <indent.h>
-#include <nearly_zero.h>
-#include <cmath.h>
+#include "luse.h"
+#include "indent.h"
+#include "nearly_zero.h"
+#include "cmath.h"
 
 class Datagram;
 class DatagramIterator;
diff --git a/panda/src/mathutil/plane_src.I b/panda/src/mathutil/plane_src.I
index e1ca6989ab..587b3183c6 100644
--- a/panda/src/mathutil/plane_src.I
+++ b/panda/src/mathutil/plane_src.I
@@ -18,7 +18,7 @@
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::Constructor
-//       Access: Public
+//       Access: Published
 //  Description: Creates a default plane.  This plane happens to
 //               intersect the origin, perpendicular to the Z axis.
 //               It's not clear how useful a default plane is.
@@ -33,7 +33,7 @@ FLOATNAME(Plane)(void) {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::Copy Constructor
-//       Access: Public
+//       Access: Published
 //  Description:
 ////////////////////////////////////////////////////////////////////
 INLINE_MATHUTIL FLOATNAME(Plane)::
@@ -47,7 +47,7 @@ FLOATNAME(Plane)(const FLOATNAME(Plane) &copy) :
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::Constructor
-//       Access: Public
+//       Access: Published
 //  Description: Constructs a plane given three counter-clockwise
 //               points, as seen from the front of the plane (that is,
 //               viewed from the end of the normal vector, looking
@@ -68,7 +68,7 @@ FLOATNAME(Plane)(const FLOATNAME(LPoint3) &a, const FLOATNAME(LPoint3) &b,
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::Constructor
-//       Access: Public
+//       Access: Published
 //  Description: Constructs a plane given a surface normal vector and
 //               a point within the plane.
 ////////////////////////////////////////////////////////////////////
@@ -85,7 +85,7 @@ FLOATNAME(Plane)(const FLOATNAME(LVector3) &normal,
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::Constructor
-//       Access: Public
+//       Access: Published
 //  Description: Constructs a plane given the four terms of the plane
 //               equation.
 ////////////////////////////////////////////////////////////////////
@@ -100,7 +100,7 @@ FLOATNAME(Plane)(FLOATTYPE a, FLOATTYPE b, FLOATTYPE c, FLOATTYPE d) :
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::Operator =
-//       Access: Public
+//       Access: Published
 //  Description:
 ////////////////////////////////////////////////////////////////////
 INLINE_MATHUTIL FLOATNAME(Plane)& FLOATNAME(Plane)::
@@ -114,7 +114,7 @@ operator = (const FLOATNAME(Plane)& p) {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::Operator * LMatrix3
-//       Access: Public
+//       Access: Published
 //  Description: Transforms the plane by the indicated matrix.
 ////////////////////////////////////////////////////////////////////
 INLINE_MATHUTIL FLOATNAME(Plane) FLOATNAME(Plane)::
@@ -126,7 +126,7 @@ operator * (const FLOATNAME(LMatrix3) &mat) const {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::Operator * LMatrix4
-//       Access: Public
+//       Access: Published
 //  Description: Transforms the plane by the indicated matrix.
 ////////////////////////////////////////////////////////////////////
 INLINE_MATHUTIL FLOATNAME(Plane) FLOATNAME(Plane)::
@@ -138,7 +138,7 @@ operator * (const FLOATNAME(LMatrix4) &mat) const {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::get_normal
-//       Access: Public
+//       Access: Published
 //  Description: Returns the surface normal of the plane.
 ////////////////////////////////////////////////////////////////////
 INLINE_MATHUTIL FLOATNAME(LVector3) FLOATNAME(Plane)::
@@ -148,7 +148,7 @@ get_normal() const {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::dist_to_plane
-//       Access: Public
+//       Access: Published
 //  Description: Returns the straight-line shortest distance from the
 //               point to the plane.  The returned value is positive
 //               if the point is in front of the plane (on the side
@@ -163,7 +163,7 @@ dist_to_plane(const FLOATNAME(LPoint3) &point) const {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::intersects_line
-//       Access: Public
+//       Access: Published
 //  Description: Returns true if the plane intersects the infinite
 //               line passing through points p1 and p2, false if the
 //               line is parallel.  The points p1 and p2 are used only
@@ -185,7 +185,7 @@ intersects_line(FLOATNAME(LPoint3) &intersection_point,
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::intersects_line
-//       Access: Public
+//       Access: Published
 //  Description: This flavor of intersects_line() returns a bit more
 //               information about the nature of the intersecting
 //               point.  The line is defined via the parametric
@@ -215,7 +215,7 @@ intersects_line(FLOATTYPE &t,
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::get_data
-//       Access: Public
+//       Access: Published
 //  Description: Returns the address of the first of the four data
 //               elements in the plane equation.  The remaining
 //               elements occupy the next positions consecutively in
@@ -228,7 +228,7 @@ get_data() const {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::get_num_components
-//       Access: Public
+//       Access: Published
 //  Description: Returns the number of elements in the plane equation,
 //               four.
 ////////////////////////////////////////////////////////////////////
@@ -239,7 +239,7 @@ get_num_components() const {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::output
-//       Access: Public
+//       Access: Published
 //  Description:
 ////////////////////////////////////////////////////////////////////
 INLINE_MATHUTIL void FLOATNAME(Plane)::
@@ -249,7 +249,7 @@ output(ostream &out) const {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::write
-//       Access: Public
+//       Access: Published
 //  Description:
 ////////////////////////////////////////////////////////////////////
 INLINE_MATHUTIL void FLOATNAME(Plane)::
diff --git a/panda/src/mathutil/plane_src.cxx b/panda/src/mathutil/plane_src.cxx
index 64ec16efc1..8fe770e6e5 100644
--- a/panda/src/mathutil/plane_src.cxx
+++ b/panda/src/mathutil/plane_src.cxx
@@ -19,7 +19,7 @@
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::get_reflection_mat
-//       Access: Public
+//       Access: Published
 //  Description: This computes a transform matrix that performs the
 //               perspective transform defined by the frustum,
 //               accordinate to the indicated coordinate system.
@@ -39,7 +39,7 @@ get_reflection_mat(void) const {
 
 ////////////////////////////////////////////////////////////////////
 //     Function: Plane::get_point
-//       Access: Public
+//       Access: Published
 //  Description: Returns an arbitrary point in the plane.  This can be
 //               used along with the normal returned by get_normal()
 //               to reconstruct the plane.
@@ -58,3 +58,42 @@ get_point() const {
     return FLOATNAME(LPoint3)(0.0f, 0.0f, -_d / _c);
   }
 }
+
+
+////////////////////////////////////////////////////////////////////
+//     Function: Plane::intersects_plane
+//       Access: Published
+//  Description: Returns true if the two planes intersect, false if
+//               they do not.  If they do intersect, then from and
+//               delta are filled in with the parametric
+//               representation of the line of intersection: that is,
+//               from is a point on that line, and delta is a vector
+//               showing the direction of the line.
+////////////////////////////////////////////////////////////////////
+bool FLOATNAME(Plane)::
+intersects_plane(FLOATNAME(LPoint3) &from,
+                 FLOATNAME(LVector3) &delta,
+                 const FLOATNAME(Plane) &other) const {
+  FLOATNAME(LVector3) n1 = get_normal();
+  FLOATNAME(LVector3) n2 = other.get_normal();
+
+  // The delta will be the cross product of the planes' normals.
+  delta = cross(n1, n2);
+
+  // If the delta came out to zero, the planes were parallel and do
+  // not intersect.
+  if (delta.almost_equal(FLOATNAME(LVector3)::zero())) {
+    return false;
+  }
+
+  FLOATTYPE n1n1 = dot(n1, n1);
+  FLOATTYPE n2n2 = dot(n2, n2);
+  FLOATTYPE n1n2 = dot(n1, n2);
+ 
+  FLOATTYPE determinant_inv = 1.0f / (n1n1 * n2n2 - n1n2 * n1n2);
+  FLOATTYPE c1 = (other._d * n1n2 - _d * n2n2) * determinant_inv;
+  FLOATTYPE c2 = (_d * n1n2 - other._d * n1n1) * determinant_inv;
+  from = n1 * c1 + n2 * c2;
+
+  return true;
+}
diff --git a/panda/src/mathutil/plane_src.h b/panda/src/mathutil/plane_src.h
index 4104ac8e15..fbacf3ccd5 100644
--- a/panda/src/mathutil/plane_src.h
+++ b/panda/src/mathutil/plane_src.h
@@ -18,7 +18,8 @@
 
 ////////////////////////////////////////////////////////////////////
 //       Class : Plane
-// Description :
+// Description : An abstract mathematical description of a plane.  A
+//               plane is defined by the equation Ax + By + Cz + D = 0.
 ////////////////////////////////////////////////////////////////////
 class EXPCL_PANDA FLOATNAME(Plane) {
 PUBLISHED:
@@ -50,6 +51,10 @@ PUBLISHED:
                               const FLOATNAME(LPoint3) &from,
                               const FLOATNAME(LVector3) &delta) const;
 
+  bool intersects_plane(FLOATNAME(LPoint3) &from,
+                        FLOATNAME(LVector3) &delta,
+                        const FLOATNAME(Plane) &other) const;
+
   INLINE_MATHUTIL const FLOATTYPE *get_data() const;
   INLINE_MATHUTIL int get_num_components() const;
 
diff --git a/panda/src/mathutil/test_mathutil.cxx b/panda/src/mathutil/test_mathutil.cxx
index f4accfb8a5..70ab8ddcd8 100644
--- a/panda/src/mathutil/test_mathutil.cxx
+++ b/panda/src/mathutil/test_mathutil.cxx
@@ -16,13 +16,27 @@
 //
 ////////////////////////////////////////////////////////////////////
 
-#include <luse.h>
+#include "luse.h"
 #include "rotate_to.h"
 #include "boundingLine.h"
 #include "boundingSphere.h"
+#include "plane.h"
+
 
 int
 main() {
+  Planef p1(LVector3f(1, 0, 0), LPoint3f(1, 0, 0));
+  Planef p2(LVector3f(0, 0, 1), LPoint3f(1, 0, 0));
+
+  LPoint3f from;
+  LVector3f delta;
+
+  if (p1.intersects_plane(from, delta, p2)) {
+    nout << "intersects, " << from << " to " << delta << "\n";
+  } else {
+    nout << "no intersect\n";
+  }
+
   /*
   LVector3d a(1.0f, 0.0f, 0.0f);
   LVector3d b = normalize(LVector3d(0.5, 0.5, 0.0f));
@@ -43,6 +57,7 @@ main() {
        << " length " << length(a * invert(rot)) << "\n";
   */
 
+  /*
   BoundingLine line(LPoint3f(0, 0, 1), LPoint3f(0, 0, 0));
 
   BoundingSphere s1(LPoint3f(0, 0, 10), 1);
@@ -54,6 +69,7 @@ main() {
   line.contains(&s2);
   line.contains(&s3);
   line.contains(&s4);
+  */
 
   /*
   s1.contains(LPoint3f(0, 0, 1), LPoint3f(0, 0, 0));