From 26a198599263f07a70aee18c9144817f15d07cf6 Mon Sep 17 00:00:00 2001
From: David Rose <david@ddrose.com>
Date: Tue, 16 Oct 2007 19:08:46 +0000
Subject: [PATCH] fix nearly-parallel case

---
 panda/src/mathutil/plane_src.cxx | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/panda/src/mathutil/plane_src.cxx b/panda/src/mathutil/plane_src.cxx
index e12cc93705..73e0861d9c 100644
--- a/panda/src/mathutil/plane_src.cxx
+++ b/panda/src/mathutil/plane_src.cxx
@@ -135,6 +135,11 @@ intersects_parabola(FLOATTYPE &t1, FLOATTYPE &t2,
   FLOATTYPE b = normal.dot(parabola.get_b());
   FLOATTYPE c = normal.dot(parabola.get_c()) + _v.v._3;
 
+  if (IS_NEARLY_ZERO(a)) {
+    // No intersection.
+    return false;
+  }
+
   // Now use the quadratic equation to solve for t.
   FLOATTYPE discriminant = b * b - 4.0 * a * c;
   if (discriminant < 0.0f) {