From 0306f2c5b9f372ed309aba3bfa73b752e6178424 Mon Sep 17 00:00:00 2001
From: rambetter <rambetter>
Date: Mon, 10 Jan 2011 05:38:30 +0000
Subject: [PATCH] Getting ready to commit Rambetter-math-fix-experiments branch
 changes to trunk, as pertaining to q3map2.  Some last-minute changes:

- EXPERIMENTAL_HIGH_PRECISION_MATH_Q3MAP2_FIXES, EXPERIMENTAL_SNAP_NORMAL_FIX,
and EXPERIMENTAL_SNAP_PLANE_FIX all set to 0 to make sure stuff in trunk
uses old "broken but stable" code, at least initially until there is further
testing done and/or some decision is made about which code to use.

- Fixing small typo in comment in PlaneEqual() in map.c.

- In comment to BaseWindingForPlane() function, describing why the old
function is broken as far as accuracy goes.  This used to be a TODO.

- VectorIsOnAxialPlane() function comment fixed	in mathlib.c.


git-svn-id: svn://svn.icculus.org/gtkradiant/GtkRadiant/branches/Rambetter-math-fix-experiments@415 8a3a26a2-13c4-0310-b231-cf6edde360e5
---
 libs/mathlib/mathlib.c        | 2 +-
 tools/quake3/common/polylib.c | 9 ++++++++-
 tools/quake3/q3map2/map.c     | 2 +-
 tools/quake3/q3map2/q3map2.h  | 6 +++---
 4 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/libs/mathlib/mathlib.c b/libs/mathlib/mathlib.c
index 8c9196e..0738c9c 100644
--- a/libs/mathlib/mathlib.c
+++ b/libs/mathlib/mathlib.c
@@ -55,7 +55,7 @@ qboolean VectorIsOnAxis(vec3_t v)
 
 /*
 ================
-VectorIsOnAxis
+VectorIsOnAxialPlane
 ================
 */
 qboolean VectorIsOnAxialPlane(vec3_t v)
diff --git a/tools/quake3/common/polylib.c b/tools/quake3/common/polylib.c
index 4413466..3788f27 100644
--- a/tools/quake3/common/polylib.c
+++ b/tools/quake3/common/polylib.c
@@ -371,7 +371,14 @@ winding_accu_t *BaseWindingForPlaneAccu(vec3_t normal, vec_t dist)
 BaseWindingForPlane
 
 Original BaseWindingForPlane() function that has serious accuracy problems.  Here is why.
-TODO: Explain why.
+The base winding is computed as a rectangle with very large coordinates.  These coordinates
+are in the range 2^17 or 2^18.  "Epsilon" (meaning the distance between two adjacent numbers)
+at these magnitudes in 32 bit floating point world is about 0.02.  So for example, if things
+go badly (by bad luck), then the whole plane could be shifted by 0.02 units (its distance could
+be off by that much).  Then if we were to compute the winding of this plane and another of
+the brush's planes met this winding at a very acute angle, that error could multiply to around
+0.1 or more when computing the final vertex coordinates of the winding.  0.1 is a very large
+error, and can lead to all sorts of disappearing triangle problems.
 =================
 */
 winding_t *BaseWindingForPlane(vec3_t normal, vec_t dist)
diff --git a/tools/quake3/q3map2/map.c b/tools/quake3/q3map2/map.c
index 5978b0b..330e2de 100644
--- a/tools/quake3/q3map2/map.c
+++ b/tools/quake3/q3map2/map.c
@@ -69,7 +69,7 @@ qboolean PlaneEqual( plane_t *p, vec3_t normal, vec_t dist )
 	de = distanceEpsilon;
 	
 	/* compare */
-	// We check equality of each component since the we're using '<', not '<='
+	// We check equality of each component since we're using '<', not '<='
 	// (the epsilons may be zero).  We want to use '<' intead of '<=' to be
 	// consistent with the true meaning of "epsilon", and also because other
 	// parts of the code uses this inequality.
diff --git a/tools/quake3/q3map2/q3map2.h b/tools/quake3/q3map2/q3map2.h
index 654716b..e3de7b7 100644
--- a/tools/quake3/q3map2/q3map2.h
+++ b/tools/quake3/q3map2/q3map2.h
@@ -123,9 +123,9 @@ constants
 ------------------------------------------------------------------------------- */
 
 /* temporary hacks and tests (please keep off in SVN to prevent anyone's legacy map from screwing up) */
-#define EXPERIMENTAL_HIGH_PRECISION_MATH_Q3MAP2_FIXES	1
-#define EXPERIMENTAL_SNAP_NORMAL_FIX			1
-#define EXPERIMENTAL_SNAP_PLANE_FIX			1
+#define EXPERIMENTAL_HIGH_PRECISION_MATH_Q3MAP2_FIXES	0
+#define EXPERIMENTAL_SNAP_NORMAL_FIX			0
+#define EXPERIMENTAL_SNAP_PLANE_FIX			0
 
 /* general */
 #define MAX_QPATH				64