auto r1 = fRay( vec3(1,2,3), vec3(2,3,4) );
auto r2 = fRay( vec3(4,5,6), vec3(5,2,3) );
auto rs = fRay( vec3(5,7,9), vec3(7,5,7) );
assert( r1 + r2 == rs );
auto s = fRay( vec3(2,0,0), vec3(-4,4,0) );
auto p = vec3( 0,0,0 );
auto r = s.altitude(p);
assert( eq( p, r.end ) );
assert( eq( r.pos, vec3(1,1,0) ) );
auto s1 = fRay( vec3(-2,0,0), vec3(1,0,0) );
auto s2 = fRay( vec3(0,0,2), vec3(0,1,-1) );
auto a1 = s1.altitude(s2);
assert( eq_seg( a1, fRay(vec3(0,0,0), vec3(0,1,1)) ) );
auto s1 = fRay( vec3(0,0,0), vec3(2,2,0) );
auto s2 = fRay( vec3(2,0,0), vec3(-4,4,0) );
assert( eq( s1.intersect(s2), s2.intersect(s1) ) );
assert( eq( s1.intersect(s2), vec3(1,1,0) ) );