Rewriting BaseWindingForPlane() in polylib.c from the ground up. The behavior

is totally unchanged, and I verified this by running extensive tests.  The
only difference is that the math precision is much much better now.
Performance should be better as well (but that is not tested).
This is a major milestone because it fixes two regression tests:
disappearing_sliver2 and sparkly_seam.
Improvements to math precision is ongoing and more improvements can probably
be made even after this patch.
I will update the README.txt files in the regression tests in a separate
commit.  This commit only includes the actual fixed code.


git-svn-id: svn://svn.icculus.org/gtkradiant/GtkRadiant/trunk@371 8a3a26a2-13c4-0310-b231-cf6edde360e5

libs/mathlib.h

@@ -81,6 +81,7 @@ void VectorMA( const vec3_t va, vec_t scale, const vec3_t vb, vec3_t vc );
 
 void _CrossProduct (vec3_t v1, vec3_t v2, vec3_t cross);
 vec_t VectorNormalize (const vec3_t in, vec3_t out);
+vec_t VectorSetLength (const vec3_t in, vec_t length, vec3_t out);
 vec_t ColorNormalize( const vec3_t in, vec3_t out );
 void VectorInverse (vec3_t v);
 void VectorPolar(vec3_t v, float radius, float theta, float phi);

libs/mathlib/mathlib.c

@@ -143,6 +143,21 @@ vec_t VectorNormalize( const vec3_t in, vec3_t out ) {
 	return length;
 }
 
+vec_t VectorSetLength(const vec3_t in, vec_t length, vec3_t out) {
+	vec_t	origLength;
+
+	origLength = (vec_t) sqrt((in[0] * in[0]) + (in[1] * in[1]) + (in[2] * in[2]));
+	if (origLength == 0)
+	{
+		VectorClear(out);
+		return 0;
+	}
+
+	VectorScale(in, length / origLength, out);
+
+	return origLength;
+}
+
 vec_t ColorNormalize( const vec3_t in, vec3_t out ) {
 	float	max, scale;
 

tools/quake3/common/polylib.c

@@ -207,6 +207,83 @@ BaseWindingForPlane
 =================
 */
 winding_t *BaseWindingForPlane (vec3_t normal, vec_t dist)
+{
+	// The goal in this function is to replicate the exact behavior that was in the original
+	// BaseWindingForPlane() function (see below).  The only thing we're going to change is the
+	// accuracy of the operation.  The original code gave a preference for the vup vector to start
+	// out as (0, 0, 1), unless the normal had a dominant Z value, in which case vup started out
+	// as (1, 0, 0).  After that, vup was "bent" [along the plane defined by normal and vup] to
+	// become perpendicular to normal.  After that the vright vector was computed as the cross
+	// product of vup and normal.
+
+	// Once these vectors are calculated, I'm constructing the winding points in exactly the same
+	// way as was done in the original function.  Orientation is the same.
+
+	// Note that the 4 points in the returned winding_t may actually not be necessary (3 might
+	// be enough).  However, I want to minimize the chance of ANY bugs popping up due to any
+	// change in behavior of this function.  Therefore, behavior stays exactly the same, except
+	// for precision of math.  Performance might be better in the new function as well.
+
+	int		x, i;
+	vec_t		max, v;
+	vec3_t		vright, vup, org;
+	winding_t	*w;
+
+	max = -BOGUS_RANGE;
+	x = -1;
+	for (i = 0; i < 3; i++) {
+		v = fabs(normal[i]);
+		if (v > max) {
+			x = i;
+			max = v;
+		}
+	}
+	if (x == -1) Error("BaseWindingForPlane: no axis found");
+
+	switch (x) {
+		case 0: // Fall through to next case.
+		case 1:
+			vright[0] = -normal[1];
+			vright[1] = normal[0];
+			vright[2] = 0;
+			break;
+		case 2:
+			vright[0] = 0;
+			vright[1] = -normal[2];
+			vright[2] = normal[1];
+			break;
+	}
+	CrossProduct(normal, vright, vup);
+
+	// IMPORTANT NOTE: vright and vup are NOT unit vectors at this point.
+	// However, normal, vup, and vright are pairwise perpendicular.
+
+	VectorSetLength(vup, MAX_WORLD_COORD * 2, vup);
+	VectorSetLength(vright, MAX_WORLD_COORD * 2, vright);
+	VectorScale(normal, dist, org);
+
+	w = AllocWinding(4);
+
+	VectorSubtract(org, vright, w->p[0]);
+	VectorAdd(w->p[0], vup, w->p[0]);
+
+	VectorAdd(org, vright, w->p[1]);
+	VectorAdd(w->p[1], vup, w->p[1]);
+
+	VectorAdd(org, vright, w->p[2]);
+	VectorSubtract(w->p[2], vup, w->p[2]);
+
+	VectorSubtract(org, vright, w->p[3]);
+	VectorSubtract(w->p[3], vup, w->p[3]);
+
+	w->numpoints = 4;
+
+	return w;
+}
+
+// Old function, not used but here for reference.  Please do not modify it.
+// (You may remove it at some point.)
+winding_t *_BaseWindingForPlane_orig_(vec3_t normal, vec_t dist)
 {
 	int		i, x;
 	vec_t	max, v;