From b95096b3d0410a89dd1d4c96bbd56c90b71c69f2 Mon Sep 17 00:00:00 2001
From: havoc <havoc@d7cf8633-e32d-0410-b094-e92efae38249>
Date: Mon, 30 Aug 2004 09:27:10 +0000
Subject: [PATCH] fixed severe bugs in QuadForPlane (broken axis selection and
 use of the wrong planenormal components in some math) modified Divide to not
 rotate the point list, this is a minor un-optimization of the algorithm but
 should improve consistency (unclipped polygons come out the same as they went
 in)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@4404 d7cf8633-e32d-0410-b094-e92efae38249
---
 polygon.c | 30 ++++++++++++------------------
 1 file changed, 12 insertions(+), 18 deletions(-)

diff --git a/polygon.c b/polygon.c
index 8133dce3..1a4f0797 100644
--- a/polygon.c
+++ b/polygon.c
@@ -9,7 +9,7 @@ Polygon clipping routines written by Forest Hale and placed into public domain.
 void PolygonF_QuadForPlane(float *outpoints, float planenormalx, float planenormaly, float planenormalz, float planedist, float quadsize)
 {
 	float d, quadright[3], quadup[3];
-	if (planenormalz > planenormalx && planenormalz > planenormaly)
+	if (fabs(planenormalz) > fabs(planenormalx) && fabs(planenormalz) > fabs(planenormaly))
 	{
 		quadup[0] = 1;
 		quadup[1] = 0;
@@ -25,8 +25,8 @@ void PolygonF_QuadForPlane(float *outpoints, float planenormalx, float planenorm
 	d = -(quadup[0] * planenormalx + quadup[1] * planenormaly + quadup[2] * planenormalz);
 	// VectorMA(quadup, d, planenormal, quadup);
 	quadup[0] += d * planenormalx;
-	quadup[1] += d * planenormalx;
-	quadup[2] += d * planenormalx;
+	quadup[1] += d * planenormaly;
+	quadup[2] += d * planenormalz;
 	// VectorNormalize(quadup);
 	d = 1.0 / sqrt(quadup[0] * quadup[0] + quadup[1] * quadup[1] + quadup[2] * quadup[2]);
 	quadup[0] *= d;
@@ -54,7 +54,7 @@ void PolygonF_QuadForPlane(float *outpoints, float planenormalx, float planenorm
 void PolygonD_QuadForPlane(double *outpoints, double planenormalx, double planenormaly, double planenormalz, double planedist, double quadsize)
 {
 	double d, quadright[3], quadup[3];
-	if (planenormalz > planenormalx && planenormalz > planenormaly)
+	if (fabs(planenormalz) > fabs(planenormalx) && fabs(planenormalz) > fabs(planenormaly))
 	{
 		quadup[0] = 1;
 		quadup[1] = 0;
@@ -70,8 +70,8 @@ void PolygonD_QuadForPlane(double *outpoints, double planenormalx, double planen
 	d = -(quadup[0] * planenormalx + quadup[1] * planenormaly + quadup[2] * planenormalz);
 	// VectorMA(quadup, d, planenormal, quadup);
 	quadup[0] += d * planenormalx;
-	quadup[1] += d * planenormalx;
-	quadup[2] += d * planenormalx;
+	quadup[1] += d * planenormaly;
+	quadup[2] += d * planenormalz;
 	// VectorNormalize(quadup);
 	d = 1.0 / sqrt(quadup[0] * quadup[0] + quadup[1] * quadup[1] + quadup[2] * quadup[2]);
 	quadup[0] *= d;
@@ -103,11 +103,11 @@ void PolygonF_Divide(unsigned int innumpoints, const float *inpoints, float plan
 	float frac, pdist, ndist;
 	frontcount = 0;
 	backcount = 0;
-	p = inpoints + (innumpoints - 1) * 3;
-	n = inpoints;
-	pdist = p[0] * planenormalx + p[1] * planenormaly + p[2] * planenormalz - planedist;
 	for (i = 0;i < innumpoints;i++)
 	{
+		p = inpoints + i * 3;
+		n = inpoints + ((i + 1) < innumpoints ? (i + 1) : 0) * 3;
+		pdist = p[0] * planenormalx + p[1] * planenormaly + p[2] * planenormalz - planedist;
 		ndist = n[0] * planenormalx + n[1] * planenormaly + n[2] * planenormalz - planedist;
 		if (pdist >= -epsilon)
 		{
@@ -147,9 +147,6 @@ void PolygonF_Divide(unsigned int innumpoints, const float *inpoints, float plan
 			}
 			backcount++;
 		}
-		p = n;
-		n += 3;
-		pdist = ndist;
 	}
 	if (neededfrontpoints)
 		*neededfrontpoints = frontcount;
@@ -164,11 +161,11 @@ void PolygonD_Divide(unsigned int innumpoints, const double *inpoints, double pl
 	double frac, pdist, ndist;
 	frontcount = 0;
 	backcount = 0;
-	p = inpoints + (innumpoints - 1) * 3;
-	n = inpoints;
-	pdist = p[0] * planenormalx + p[1] * planenormaly + p[2] * planenormalz - planedist;
 	for (i = 0;i < innumpoints;i++)
 	{
+		p = inpoints + i * 3;
+		n = inpoints + ((i + 1) < innumpoints ? (i + 1) : 0) * 3;
+		pdist = p[0] * planenormalx + p[1] * planenormaly + p[2] * planenormalz - planedist;
 		ndist = n[0] * planenormalx + n[1] * planenormaly + n[2] * planenormalz - planedist;
 		if (pdist >= -epsilon)
 		{
@@ -208,9 +205,6 @@ void PolygonD_Divide(unsigned int innumpoints, const double *inpoints, double pl
 			}
 			backcount++;
 		}
-		p = n;
-		n += 3;
-		pdist = ndist;
 	}
 	if (neededfrontpoints)
 		*neededfrontpoints = frontcount;
-- 
2.39.2