1 files changed, 90 insertions, 0 deletions
diff --git a/quaternion.c b/quaternion.c
new file mode 100644
index 0000000..3297788
--- /dev/null
+++ b/quaternion.c
@@ -0,0 +1,90 @@
+#include <u.h>
+#include <libc.h>
+#include <geometry.h>
+
+Quaternion
+Quat(double r, double i, double j, double k)
+{
+	return (Quaternion){r, i, j, k};
+}
+
+Quaternion
+Quatvec(double s, Point3 v)
+{
+	return (Quaternion){s, v.x, v.y, v.z};
+}
+
+Quaternion
+addq(Quaternion a, Quaternion b)
+{
+	return (Quaternion){a.r+b.r, a.i+b.i, a.j+b.j, a.k+b.k};
+}
+
+Quaternion
+subq(Quaternion a, Quaternion b)
+{
+	return (Quaternion){a.r-b.r, a.i-b.i, a.j-b.j, a.k-b.k};
+}
+
+Quaternion
+mulq(Quaternion q, Quaternion r)
+{
+	Point3 qv, rv, tmp;
+
+	qv = Vec3(q.i, q.j, q.k);
+	rv = Vec3(r.i, r.j, r.k);
+	tmp = addpt3(addpt3(mulpt3(rv, q.r), mulpt3(qv, r.r)), crossvec3(qv, rv));
+	return (Quaternion){q.r*r.r - dotvec3(qv, rv), tmp.x, tmp.y, tmp.z};
+}
+
+Quaternion
+smulq(Quaternion q, double s)
+{
+	return (Quaternion){q.r*s, q.i*s, q.j*s, q.k*s};
+}
+
+Quaternion
+sdivq(Quaternion q, double s)
+{
+	return (Quaternion){q.r/s, q.i/s, q.j/s, q.k/s};
+}
+
+double
+dotq(Quaternion q, Quaternion r)
+{
+	return q.r*r.r + q.i*r.i + q.j*r.j + q.k*r.k;
+}
+
+Quaternion
+invq(Quaternion q)
+{
+	double len²;
+
+	len² = dotq(q, q);
+	if(len² == 0)
+		return (Quaternion){0, 0, 0, 0};
+	return (Quaternion){q.r/len², -q.i/len², -q.j/len², -q.k/len²};
+}
+
+double
+qlen(Quaternion q)
+{
+	return sqrt(q.r*q.r + q.i*q.i + q.j*q.j + q.k*q.k);
+}
+
+Quaternion
+normq(Quaternion q)
+{
+	return sdivq(q, qlen(q));
+}
+
+Point3
+qrotate(Point3 p, Point3 axis, double angle)
+{
+	Quaternion qaxis, qr;
+
+	angle /= 2;
+	qaxis = Quatvec(cos(angle), mulpt3(axis, sin(angle)));
+	qr = mulq(mulq(qaxis, Quatvec(0, p)), invq(qaxis));
+	return Vec3(qr.i, qr.j, qr.k);
+}