From fbdc4ee8d5a87da8276816edbfb14ac1371fd59f Mon Sep 17 00:00:00 2001 From: cutealien Date: Sun, 30 Jul 2023 16:34:24 +0000 Subject: [PATCH] Optimization in quaternion::rotationFromTo from Robert Eisele Turns out we can avoid a square root and a division. Patch comes even with proof: https://raw.org/proof/quaternion-from-two-vectors (I also tested it a while and indeed got same results) git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6511 dfc29bdd-3216-0410-991c-e03cc46cb475 --- include/quaternion.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/include/quaternion.h b/include/quaternion.h index 0be0b552..0d2beb98 100644 --- a/include/quaternion.h +++ b/include/quaternion.h @@ -720,6 +720,8 @@ inline core::quaternion& quaternion::makeIdentity() inline core::quaternion& quaternion::rotationFromTo(const vector3df& from, const vector3df& to) { // Based on Stan Melax's article in Game Programming Gems + // Optimized by Robert Eisele: https://raw.org/proof/quaternion-from-two-vectors + // Copy, since cannot modify local vector3df v0 = from; vector3df v1 = to; @@ -744,10 +746,8 @@ inline core::quaternion& quaternion::rotationFromTo(const vector3df& from, const return set(axis.X, axis.Y, axis.Z, 0).normalize(); } - const f32 s = sqrtf( (1+d)*2 ); // optimize inv_sqrt - const f32 invs = 1.f / s; - const vector3df c = v0.crossProduct(v1)*invs; - return set(c.X, c.Y, c.Z, s * 0.5f).normalize(); + const vector3df c = v0.crossProduct(v1); + return set(c.X, c.Y, c.Z, 1 + d).normalize(); }