static void simulate_trackball(quat *q, GLfloat p1x, GLfloat p1y, GLfloat p2x, GLfloat p2y) {
if (p1x == p2x && p1y == p2y) {
quat_identity(q);
}
else {
quat p1, p2, a, d;
float p1z, p2z;
float s, t;
p1z = project_to_sphere(p1x, p1y);
quat_assign(&p1, 0.0, p1x, p1y, p1z);
p2z = project_to_sphere(p2x, p2y);
quat_assign(&p2, 0.0, p2x, p2y, p2z);
quat_mul(&a, &p1, &p2);
a.w = 0.0;
s = quat_norm(&a);
quat_div_real(&a, &a, s);
quat_sub(&d, &p1, &p2);
t = quat_norm(&d) / (2.0 * R * ROOT_2_INV);
if (t > 1.0) t = 1.0;
quat_assign(q, cos(asin(t)), a.x * t, a.y * t, a.z * t);
}
}
void trackball::
rotate(double fx, double fy, double tx, double ty) {
scm::math::vec3d start(fx, fy, project_to_sphere(fx, fy));
scm::math::vec3d end(tx, ty, project_to_sphere(tx, ty));
scm::math::vec3d diff(end - start);
double diff_len = scm::math::length(diff);
scm::math::vec3d rot_axis(cross(start, end));
double rot_angle = 2.0 * asin(scm::math::clamp(diff_len/(2.0 * radius_), -1.0, 1.0));
scm::math::mat4d tmp(scm::math::mat4d::identity());
scm::math::mat4d tmp_dolly(scm::math::mat4d::identity());
scm::math::mat4d tmp_dolly_inv(scm::math::mat4d::identity());
scm::math::translate(tmp_dolly, 0.0, 0.0, dolly_);
scm::math::translate(tmp_dolly_inv, 0.0, 0.0, -dolly_);
scm::math::rotate(tmp, scm::math::rad2deg(rot_angle), rot_axis);
transform_ = tmp_dolly * tmp * tmp_dolly_inv * transform_;
}
