Mirrors and reflective surfaces really seem to be a struggle in modern-day games unless you are using RT, and of course, that has a huge performance penalty so I am quite curious why these techniques that were used in the 90s have fallen out of favour for other techniques that produce significantly worse results visually.
In: Technology
It’s very expensive. Unreal did have this feature in Unreal 4, it was called “planar reflections” and it tanked performance. It was mostly made for scenes that did not need to run in real time (like artists personal work). And it can only work across a plane (like a mirror or a lake). Things like Lumen reflections, probes, or sphere captures are drastically cheaper and most people won’t notice the visual difference (but will notice the performance impact).
Even if you could somehow make planar reflections performant, you would still need 99% of your reflections to use a different method, because literally every surface in a modern video game is reflective to a certain point, and so reflections need to work on any shape of surface. Why is every surface in modern games reflective? Because that’s how it works in real life! Sure, something like smooth plastic or metal is obviously reflective, but even things like dirt and rubber are reflective in real life, even if it’s only a few percent as reflective as a mirror. Reflectivity is how we see things. Light hits a surface, reflects off, and hits our eye. One of the things that makes physically based rendering materials look so much more realistic than older style materials is the fact that PBR rendering is based on reflections.
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