SharpMuPDF/mupdf/thirdparty/freeglut/progs/demos/spaceball/vmath.c

#include <math.h>
#include "vmath.h"

quat_t quat_rotate(quat_t q, float angle, float x, float y, float z)
{
  quat_t rq;
  float half_angle = angle * 0.5f;
  float sin_half = (float)sin(half_angle);

  rq.w = (float)cos(half_angle);
  rq.x = x * sin_half;
  rq.y = y * sin_half;
  rq.z = z * sin_half;

  return quat_mul(q, rq);
}