void Camera :: roll(float angle)
{ // roll the camera through angle degrees
float cs = cos(3.14159265/180 * angle);
float sn = sin(3.14159265/180 * angle);
Vector3 t(u); // remember old u
u.set(cs*t.x - sn*v.x, cs*t.y - sn*v.y, cs*t.z - sn*v.z);
	v.set(sn*t.x + cs*v.x, sn*t.y + cs*v.y, sn*t.z + cs*v.z);
	setModelViewMatrix();
}