mathutil: override plane.normalize() to be meaningful for planes

Now it only divides by the length of the normal, rather than also adding in the square of the w component.

panda/src/mathutil/plane_src.I

@@ -137,6 +137,37 @@ dist_to_plane(const FLOATNAME(LPoint3) &point) const {
   return (_v(0) * point[0] + _v(1) * point[1] + _v(2) * point[2] + _v(3));
 }
 
+/**
+ * Normalizes the plane in place.  Returns true if the plane was normalized,
+ * false if the plane had a zero-length normal vector.
+ */
+INLINE_MATHUTIL bool FLOATNAME(LPlane)::
+normalize() {
+  FLOATTYPE l2 = get_normal().length_squared();
+  if (l2 == (FLOATTYPE)0.0f) {
+    return false;
+
+  } else if (!IS_THRESHOLD_EQUAL(l2, 1.0f, NEARLY_ZERO(FLOATTYPE) * NEARLY_ZERO(FLOATTYPE))) {
+    (*this) /= csqrt(l2);
+  }
+
+  return true;
+}
+
+/**
+ * Normalizes the plane and returns the normalized plane as a copy.  If the
+ * plane's normal was a zero-length vector, the same plane is returned.
+ */
+INLINE_MATHUTIL FLOATNAME(LPlane) FLOATNAME(LPlane)::
+normalized() const {
+  FLOATTYPE l2 = get_normal().length_squared();
+  if (l2 != (FLOATTYPE)0.0f) {
+    return (*this) / csqrt(l2);
+  } else {
+    return (*this);
+  }
+}
+
 /**
  * Returns the point within the plane nearest to the indicated point in space.
  */

panda/src/mathutil/plane_src.h

@@ -39,6 +39,9 @@ PUBLISHED:
   FLOATNAME(LPoint3) get_point() const;
 
   INLINE_MATHUTIL FLOATTYPE dist_to_plane(const FLOATNAME(LPoint3) &point) const;
+
+  INLINE_MATHUTIL bool normalize();
+  INLINE_MATHUTIL FLOATNAME(LPlane) normalized() const;
   INLINE_MATHUTIL FLOATNAME(LPoint3) project(const FLOATNAME(LPoint3) &point) const;
   INLINE_MATHUTIL void flip();