TLDR: see (bugs 3/4), which explain the first 2 bugs... but I'll leave them here, as they illustrate some odd behaviour.
bug 1: Found an issue with Z-culling of foreground objects. Affects both Fullscreen and Borderless Window.
FPS drops from above 60 to below 50, when the tree is culled from view. When the tree is in view, FPS remains above 60.
It's only when the tree is removed (culled) from view that FPS drops below 50.
FPS in the general area is above 60, even looking towards Vegelbuds.
At first, I thought it was related to the nearby Vegelbud Estate geometry, but this happens looking down at the ground as well as up. FPS can drop below 45 when looking up though. The results of slightly rotating the camera. No new objects come into view except the 2 trees which are either visible or culled from view.
Something in the rendering pipeline, which was probably affecting the tree stutter I noticed previously with Borderless Window mode. But, this issue affects Fullscreen as well.
Strangely, it's also affected by camera angle. It's worst at 20-30 degrees, but can return to 60 FPS at extreme vertical angles. Maybe that's to be expected, as more of the ground or sky come into view, culling more background objects from view. However, this foreground culling issue is not expected.
Well, that's even stranger... It only seems to affects certain trees. Not sure why that's the case. About half of trees in the area seem affected. Not sure based on what principle.
2 adjacent trees, or tree model? Neither. Even trees with completely different models, standing separately are affected. Not sure what the common factor is, seems random, but always the same exact trees.
There are also trees with what is apparently the same model as another, which do not suffer from the same problem.
Alright, so this even occurs if the tree is behind you, completely off the screen. As long as it is nearby and being culled by the engine, the issue persists. I was trying to figure out why FPS was dropping randomly just standing out in the open, with nearby trees, and the camera rotated a certain way, compared to another 2 feet away, and this is the reason.
In fact, FPS drops linearly for each object or tree that is culled. 1 tree = 52 fps. 2 tree = 46 fps.
bug 2: Found some other issue, related to the road textures... When I'm standing perpendicular, directly in front of it, FPS also drops to 40 from 60. Not sure if related to twigs with incorrect shaders on them (the ones that glow in the dark)... or something else with this texture specifically or LODs. The issue disappears as soon as I move across the road. The direction (left/right) from which it is viewed makes little difference. For reference, 60 FPS in Novigrad.
The road issue is definitely an Ultra+ texture resolution or LOD issue, possibly shader. It's resolved on Ultra setting. I've never seen 1 texture spanning 3% of the screen area drop FPS by 33%...
This location is by the Temerian Partisan Hideout (signpost marker visible on map), in the direction of Vegelbud Estate.
Only seems somewhat related to some ground textures on Ultra+, even those completely covered in grass, which is counter-productive, where FPS drops from 60 to 52-54 simply staring at the ground. In other areas it's fine. I cannot image this is due to resolution or LODs though, maybe pixel shaders?
bug 3: Yet one more bug. Setting texture quality to Ultra instead of Ultra+ drops FPS to 20-25, until you alt-tab out and back in. Actually, alt-tabbing back in is insufficient. You need to change the focus or press Windows key, etc... Actually, it isn't working this time around, still stuck at 30 FPS, eventually resolved.
Ok, so if it's set to Ultra, FPS will drop to 30 when setting it to Low, High or Ultra+. If it's set to Ultra+, it will drop to 30 when setting it to Medium or High. Basically alternates in even/odd sets, if Low=0, Medium=1, etc...
Changing detail level has the same effect, and possibly other options?
bug 4: This is not a new bug, but something awkward. When I load a saved game, road texture issues are temporarily resolved... the foreground culling issues are significantly reduced.
Oh well, that's what did it... alt-tabbing triggers bugs 1/2. It may also be triggered in other ways like changing video options, as someone else mentioned. From that point on, this bug persists until a saved game is loaded.
Awkwardly though, alt-tabbing doesn't always trigger the bug. There must be some other condition.
Alright, this is beyond me. Much too random. I was able to trigger it by fast-travelling, without even alt-tabbing. Maybe something to do with the game menus or UI, or some combination of alt-tabbing and fast-travelling or UIs.
I've also tested with various weather conditions, as that seems to variably affect the results. The lowest I could get it to drop was 49 FPS in front of the road, at night, with fog, rain, and wind. When the bug is triggered, it will drop to 40 FPS in front of the road, clear conditions (as in the screenshots) when it should be 60 FPS, assuming no trees are culled and the bug is not triggered. Strangely, in another test, I'm getting 60 FPS at night, with fog, rain and wind in front of the same road...
8gb vram: Well here's another oddity. My system was using 8 gb vram. Why is that strange? Because Witcher 3 doesn't use more than 4gb. Not sure if this was as a result of messing with graphics options, but the issues cropped up before that. Not sure exactly what happened there, but there was no other process running in the background. Required reboot.
This may even be responsible for the texture and FPS issues, assuming it somehow occurred before I messed with graphics options, spontaneously. I'm not sure, will monitor the situation.
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