code: function orthoProj_(pos, cam){
      var vec = V3.sub(pos, cam.pos);
      var camAxis = axis(cam);
      var normDist = V3.dot(vec, camAxis.y);
      var normProj = V3.scale(normDist, camAxis.y);
      var posOnPlane = V3.add(vec, V3_(-normProj.x, -normProj.y, -normProj.z));
      var x = V3.dot(posOnPlane, camAxis.x);
      var y = V3.dot(posOnPlane, camAxis.z);
      return V3_(x, y, normDist);
    }
docs: Vector3, Camera -> Vector3 (-1.0 to 1.0)