From b9c6d5f4f9cf3e0e8c32499959c879e6300717f6 Mon Sep 17 00:00:00 2001
From: Michael Orlitzky <michael@orlitzky.com>
Date: Sun, 28 Aug 2011 17:45:07 -0400
Subject: [PATCH] Fix the tetrahedron collision detection. Update the test for
 the collision detection (it was wrong).

---
 src/Tests/Grid.hs  | 8 ++------
 src/Tetrahedron.hs | 6 +++++-
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/Tests/Grid.hs b/src/Tests/Grid.hs
index 3cc316a..f94a519 100644
--- a/src/Tests/Grid.hs
+++ b/src/Tests/Grid.hs
@@ -360,19 +360,15 @@ test_trilinear9x9x9_reproduced =
 --
 --   Example from before the fix:
 --
---   > b0 (tetrahedron12 c) p
---   -2.168404344971019e-18
 --   > b0 (tetrahedron15 c) p
 --   -3.4694469519536365e-18
 --
 test_tetrahedra_collision_sensitivity :: Assertion
 test_tetrahedra_collision_sensitivity =
-  assertTrue "tetrahedron collision tests aren't too sensitive" $
-             contains_point t12 p &&
+  assertTrue "tetrahedron collision tests isn't too sensitive" $
              contains_point t15 p
   where
-    g = make_grid 1 trilinear
+    g = make_grid 1 naturals_1d
     c = cube_at g 0 17 1
     p = (0, 16.75, 0.5) :: Point
-    t12 = tetrahedron12 c
     t15 = tetrahedron15 c
diff --git a/src/Tetrahedron.hs b/src/Tetrahedron.hs
index 73ed588..6c13f4b 100644
--- a/src/Tetrahedron.hs
+++ b/src/Tetrahedron.hs
@@ -6,6 +6,7 @@ import Prelude hiding (LT)
 import Test.QuickCheck (Arbitrary(..), Gen)
 
 import Cardinal
+import Comparisons (nearly_ge)
 import FunctionValues
 import Misc (factorial)
 import Point
@@ -42,7 +43,10 @@ instance Show Tetrahedron where
 instance ThreeDimensional Tetrahedron where
     center t = ((v0 t) + (v1 t) + (v2 t) + (v3 t)) `scale` (1/4)
     contains_point t p =
-        (b0 t p) >= 0 && (b1 t p) >= 0 && (b2 t p) >= 0 && (b3 t p) >= 0
+      (b0 t p) `nearly_ge` 0 &&
+      (b1 t p) `nearly_ge` 0 &&
+      (b2 t p) `nearly_ge` 0 &&
+      (b3 t p) `nearly_ge` 0
 
 
 polynomial :: Tetrahedron -> (RealFunction Point)
-- 
2.43.2