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| author | Ariya Hidayat <ariya.hidayat@nokia.com> | 2009-06-30 09:18:03 (GMT) |
|---|---|---|
| committer | Ariya Hidayat <ariya.hidayat@nokia.com> | 2009-08-06 10:55:01 (GMT) |
| commit | cbc229081a9df67a577b4bea61ad6aac52d470cb (patch) | |
| tree | 36e40064b36ee8611859afd661bc5d8f80a3b205 /src | |
| parent | e3f3ced70f80369439200b7d7bc3e4e11222c81f (diff) | |
| download | Qt-cbc229081a9df67a577b4bea61ad6aac52d470cb.zip Qt-cbc229081a9df67a577b4bea61ad6aac52d470cb.tar.gz Qt-cbc229081a9df67a577b4bea61ad6aac52d470cb.tar.bz2 | |
Faster quaternion multiplications.
Use the known factorization trick to speed-up quaternion multiplication.
Now we need only 9 floating-point multiplications, instead of 16 (but
at the cost of extra additions and subtractions).
Callgrind shows that the function now takes 299 instructions instead of
318 instructions, which is not a big win. However I assume the speed-up
has a better effect for mobile CPU, where multiplications are more
expensive.
Reviewed-by: Rhys Weatherley
Diffstat (limited to 'src')
| -rw-r--r-- | src/gui/math3d/qquaternion.h | 29 |
1 files changed, 11 insertions, 18 deletions
diff --git a/src/gui/math3d/qquaternion.h b/src/gui/math3d/qquaternion.h index 55c871d..9a1b590 100644 --- a/src/gui/math3d/qquaternion.h +++ b/src/gui/math3d/qquaternion.h @@ -198,24 +198,17 @@ inline QQuaternion &QQuaternion::operator*=(qreal factor) inline const QQuaternion operator*(const QQuaternion &q1, const QQuaternion& q2) { - // Algorithm from: - // http://www.j3d.org/matrix_faq/matrfaq_latest.html#Q53 - float x = q1.wp * q2.xp + - q1.xp * q2.wp + - q1.yp * q2.zp - - q1.zp * q2.yp; - float y = q1.wp * q2.yp + - q1.yp * q2.wp + - q1.zp * q2.xp - - q1.xp * q2.zp; - float z = q1.wp * q2.zp + - q1.zp * q2.wp + - q1.xp * q2.yp - - q1.yp * q2.xp; - float w = q1.wp * q2.wp - - q1.xp * q2.xp - - q1.yp * q2.yp - - q1.zp * q2.zp; + float ww = (q1.zp + q1.xp) * (q2.xp + q2.yp); + float yy = (q1.wp - q1.yp) * (q2.wp + q2.zp); + float zz = (q1.wp + q1.yp) * (q2.wp - q2.zp); + float xx = ww + yy + zz; + float qq = 0.5 * (xx + (q1.zp - q1.xp) * (q2.xp - q2.yp)); + + float w = qq - ww + (q1.zp - q1.yp) * (q2.yp - q2.zp); + float x = qq - xx + (q1.xp + q1.wp) * (q2.xp + q2.wp); + float y = qq - yy + (q1.wp - q1.xp) * (q2.yp + q2.zp); + float z = qq - zz + (q1.zp + q1.yp) * (q2.wp - q2.xp); + return QQuaternion(w, x, y, z, 1); } |