From: Rudolf Polzer Date: Wed, 29 Dec 2010 16:37:57 +0000 (+0100) Subject: svn r377 by Rambetter: X-Git-Tag: xonotic-v0.5.0~79 X-Git-Url: https://git.rm.cloudns.org/?a=commitdiff_plain;h=7aa95f5ab555c2fe2b811a47a747ae2a2fff3f38;p=xonotic%2Fnetradiant.git svn r377 by Rambetter: Continuing work on BaseWindingForPlane() in polylib.c. In fact I'm pursuing the approach that was committed in r375 (but was then backed out). I can't believe my eyes, but I seem to be getting 0.000000% error in some of my regression tests. The trick is to scale by a power of 2 and never do a VectorNormalize(). --- diff --git a/libs/mathlib.h b/libs/mathlib.h index 1a86094d..d206d330 100644 --- a/libs/mathlib.h +++ b/libs/mathlib.h @@ -89,7 +89,6 @@ 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); diff --git a/libs/mathlib/mathlib.c b/libs/mathlib/mathlib.c index 0d134a51..7daf27b2 100644 --- a/libs/mathlib/mathlib.c +++ b/libs/mathlib/mathlib.c @@ -135,21 +135,6 @@ 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; diff --git a/tools/quake3/common/polylib.c b/tools/quake3/common/polylib.c index b62d12ff..27d64d1f 100644 --- a/tools/quake3/common/polylib.c +++ b/tools/quake3/common/polylib.c @@ -219,10 +219,8 @@ winding_t *BaseWindingForPlane (vec3_t normal, vec_t dist) // 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. + // EDIT: We're also changing the size of the winding polygon; this is a side effect of + // eliminating a VectorNormalize() call. The new winding polygon is actually bigger. int x, i; vec_t max, v; @@ -253,15 +251,42 @@ winding_t *BaseWindingForPlane (vec3_t normal, vec_t dist) vright[2] = normal[1]; break; } + // vright and normal are now perpendicular, you can prove this by taking their + // dot product and seeing that it's always exactly 0 (with no error). + + // NOTE: vright is NOT a unit vector at this point. vright will have length + // not exceeding 1.0. The minimum length that vright can achieve happens when, + // for example, the Z and X components of the normal input vector are equal, + // and when its Y component is zero. In that case Z and X of the normal vector + // are both approximately 0.70711. The resulting vright vector in this case + // will have a length of 0.70711. + + // We're relying on the fact that MAX_WORLD_COORD is a power of 2 to keep + // our calculation precise and relatively free of floating point error. + // The code will work if that's not the case, but not as well. + VectorScale(vright, MAX_WORLD_COORD * 4, vright); + + // At time time of this writing, MAX_WORLD_COORD was 65536 (2^16). Therefore + // the length of vright at this point is at least 185364. A corner of the world + // at location (65536, 65536, 65536) is distance 113512 away from the origin. + CrossProduct(normal, vright, vup); - // IMPORTANT NOTE: vright and vup are NOT unit vectors at this point. - // However, normal, vup, and vright are pairwise perpendicular. + // vup now has length equal to that of vright. - VectorSetLength(vup, MAX_WORLD_COORD * 2, vup); - VectorSetLength(vright, MAX_WORLD_COORD * 2, vright); VectorScale(normal, dist, org); + // org is now a point on the plane defined by normal and dist. Furthermore, + // org, vright, and vup are pairwise perpendicular. Now, the 4 vectors + // (+-)vright + (+-)vup have length that is at least sqrt(185364^2 + 185364^2), + // which is about 262144. That length lies outside the world, since the furthest + // point in the world has distance 113512 from the origin as mentioned above. + // Also, these 4 vectors are perpendicular to the org vector. So adding them + // to org will only increase their length. Therefore the 4 points defined below + // all lie outside of the world. Furthermore, it can be easily seen that the + // edges connecting these 4 points (in the winding_t below) lie completely outside + // the world. sqrt(262144^2 + 262144^2)/2 = 185363, which is greater than 113512. + w = AllocWinding(4); VectorSubtract(org, vright, w->p[0]);