It's "a lot of work" for the machine, but very little work for the programmer. It is assumed that rendering the scene is already fast enough to be happily inte

It's "a lot of work" for the machine, but very little work for the programmer. It is assumed that rendering the scene is already fast enough to be happily interactive for the UI. Mouse picking is a human timeline interaction. And, it's likely that the scene is static during the pick (do you want to pick a tiny, moving atom?). So, if the pick is as fast or faster than a single frame of spinning the model, it should be unnoticeably fast for the user.