In my opinion we should discourage link only answers, too.
Links to external resources are great to provide extra information to the question, e.g. like further reading material, but even if all links are broken in an answer, it should still be a helpful answer. So at least the most relevant information from behind the links should be included in the answer itself.
The information in the answer make it an answer, not the information that can be found behind a link.
I would probably cast a down vote and post a comment along the lines of
Welcome to Computer Graphics StackExchange. The links in your answer look promising, but as links tend to break over time, we discourage link-only answers. To improve your answer, consider adding the relevant information directly into your answer. Also see How do I write a good answer?How do I write a good answer?.
Depending on the other answers I'd also flag it as Not an answer, either immediately or some time later to give the user a chance to improve the post. If the post is not improved, I suggest to convert the answer to a comment.