How does TSW being a train simulator have anything to do with graphics? How a train simulator works under the hood has nothing to do with it's graphics. You can make a train simulator in OpenGL, Unity, EU, anything you want. After all, these are just game engines and you're pretty much free to code what you want. The only aspect of TSW that connects to graphics is how the routes are built up. Obviously it's similar to how TS and Trainz used to do it, compared to traditional games with completely "pre-made" maps it's totally different. I suppose it's much harder to optimize scenery loading performance, as we can see pretty much from all train simulators on the market. But that has pretty much nothing to do with lighting andenviromental effects and other things that are the worst offenders in TSW distant scenery.