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Various jittering/stuttering issues in XWA (and some fixes)

Posted: Sun Jul 18, 2021 6:28 am
by blue_max
There are a number of issues in this game, and the mod, that people have noticed and reported as "jittering". I feel like I need to document all of them in one place.

* Cockpit Inertia: This is probably the most common source of jitter. The mechanism used to implement this feature is the same the game uses for cockpit shake. We suspect this causes some jittering. You can disable this through the Babu Frik configurator or in CockpitLook.cfg, by setting "cockpit_inertia_enabled = 0"

* The game is still single-threaded and computes pretty much everything in the CPU. If the screen is busy, the framerate will drop and this can look like jittering. Try to optimize the performance of the game to mitigate this problem. See the following threads:

viewtopic.php?f=36&t=12490
viewtopic.php?f=36&t=12827

* SteamVR jittering: a number of fixes by m0rgg have been merged into the latest release of the VR mod, as of version 1.1.5.5. These fixes address tracking problems in SteamVR. Go to the downloads section and update your files, please.

* Motion Smoothing/Interleaved Reprojection/Asynchronous Reprojection: These should be set to off. Enabling these will most likely cause a lot of dropped frames in SteamVR.

* In VR, you might experience some significant framerate drops whenever you hit a target with lasers. This is a known problem and we're not sure how to fix it yet. The workaround is to disable "Hit Effects" using the in-game menus.

* You can't fly "straight up" nor "down". This game suffers from gimbal lock. We can't yet fix this. Sometimes people experience this as "jitter" when trying to fly in these directions, sometimes it's like a magnet that "repels" you from those spots.

* The background sometimes jumps around for a few pixels. We're not sure why this happens, but it may be fixed later if/when we implement support for environment maps. However, some users have reported that the background jittering is mitigated when the in-game resolution is set to a high value, like 1600x1200.

* Sometimes the edges of polygons jump when they cross the edges of the screen. This is more noticeable in cockpits. Sometimes this can be fixed by modifying the OPT and breaking up the larger triangles. This seems to be a limitation of the engine, but if this happens consistently on a specific cockpit, you can report it and we'll try to address it when we can.

* Hangar. The hangar itself is a bit problematic even without VR. If your monitor's refresh rate is set to more than 60Hz, the game may stutter in external view. The hangar also doesn't use the regular Cockpit Look hook and it is intrinsically slower. Other than limiting the monitor refresh rate (or the VR headset rate) to 60Hz, we don't have more suggestions here. If you don't experience problems in the hangar, don't modify the refresh rate.