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Currently the only known workaround is to manually tweak the file "./resources/settings.txt" which is ugly because it means messing with XP internals which will get overwritten with each update and is likely to break other things at some point.
See also this forum topic about the tweak and this dev blog for technical background.
In XP10 this was an official option in the rendering settings and I think this needs to be brought back.
IMO the main purpose for this is better support for orthophoto and HD meshes, which are getting increasingly popular due to community-provided tools like Ortho4XP and G2XPL. It is proven that in those cases extended DSF can cause a dramatic FPS impact and stuttering while transitioning between tiles due to significant increase of VRAM usage and swapping overall.
Here is just one example of a user that reported huge improvements after applying the tweak.
Ben Supnik himself has provided a reason for why this was made optional in XP10 in this comment:
In X-Plane 10 you could turn off some options to "dumb down" the sim and see performance "improvements," for example with the extended dsf option. For X-Plane 11 we focused on making the default sim the best it could be.
The thing about the dense meshes and orthophotos is that some of them are REALLY inefficient in terms of their perf cost. If your machine isn't a beast, you'll really feel the cumulative effects of all this in X-Plane 11.
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