TrackIR Stutter in DCS 2.8 at framerates other than 60 and 120 fps
Posted: Mon Aug 21, 2023 7:02 am
The issue:
At framerates other than 60 or 120 fps, there is rhythmic stuttering when looking around with TrackIR in DCS World 2.8. When not looking around using TrackIR, and instead looking around with hat switches, or mouse look, the image is perfectly smooth.
The cause:
Unknown. TrackIR has a polling rate of 120hz, which is a likely contributor to this issue, but does not explain why some titles are affected and others are not, or to varying degrees. For instance, Enabling vsync in Microsoft Flight Simulator or IL2 Great Battles, resolves this issue, or minimizes its effect to a point where it is unnoticeable. In DCS, prior to version 2.8, there was no need to enable vsync, or limit framerate, but the user could Alt+Enter to enter apparent "Exclusive Fullscreen", resolving this issue. I can confirm Alt+Enter does not fix the issue anymore, it is prevalent in both exclusive fullscreen and fullscreen.
This is a camera position issue as far as I can tell, in that the position of the camera is not updating linearly on each frame, there is a jump on certain frames and those certain frames appear to be in sequence - e.g. frame 5, 10, 15, 20. I have a video later in this post displaying this. I could deduce that some games are using a form of smoothing to predict the camera position, and bypass any erroneous position data, but I am speculating.
Research:
I first reported on this issue in 2016, in the following thread on this forum:
https://forums.naturalpoint.com/viewtopic.php?t=13991
There have been many more forum discussions since then, here are two recent ones:
https://forum.dcs.world/topic/267346-tr ... tc-solved/
https://forum.dcs.world/topic/325383-tr ... servation/
This is a difficult issue to reproduce - it requires testers run a monitor at a refresh rate greater than 60hz (more common today), and of course, capturing a video will not show the issue clearly, more often than not because the clip has been recorded at less than the in-game framerate, or framerate has been restricted by the upload platform. The only way to see it is frame-by-frame. Below is a video I have captured showing the issue, frame-by-frame.
https://youtu.be/AWHxhHa4ejI
What is noticeable, is the fact there are no real hitches or pauses in the game, but rather every five frames there is a jump or acceleration in the camera position, evident in the relative motion of the P-51 when moving from frames 4-5, 9-10, 14-15, and 19-20, respectively. Then, the very next frame (6, 11, 16, 21) shows less acceleration than all other frames. So the result is quite interesting. If we focus on one instance of stutter (frame 5), we see accelerated movement on frame 5, reduced movement on frame 6, and by frame 7 we see the expected position of the camera, which is to say, the acceleration on frame 5 and deceleration on frame 6 nullifies any gain in camera movement. This makes sense, because if the camera position simply accelerated every 5 frames, we would see a divergence of the input (head tracking) and output (camera movement), so the two must cancel out. But why is there a 'spike' in camera position every five frames?! That is the question, as removing the acceleration and deceleration between frame 5 and 6 would create linearity of movement through the frames, and stutter would be resolved.
Troubleshooting:
There is no apparent hardware issue, all indicator lights are working on the device, and there is nothing to suggest an IR issue. I have also been fortunate to borrow a friend's TrackIR5 and reproduce the issue with their device, and in multiple environments / lighting conditions.
I have lodged a ticket with Eagle Dynamics who provide the following analysis:
Your problem is not related to the fact that enter exclusive full screen was removed from DCS, since other users and our testers do not experience problems with TrackIR stuttering.This may be due to some third party software or TrackIR settings.
They expanded on troublshooting, asking me to cull a considerable number of background processes, as well as establish a new admin account on Windows. Neither of those provided any change to the issue, which isn't surprising, because I don't believe this is a 'stuttering' issue in the traditional sense. The game itself is not stuttering, it is the camera movement, or the camera movement is inducing stuttering.
I have been fortunate to build a new computer, and have been able to reproduce this issue on both old and new systems indicated below:
System 1: 4790k, 1080Ti, 16GB DDR3 1600, Windows 10 19045.3086, Nvidia Driver Version 536.23
System 2: 7800X3D, 4090, 32GB DDR5 6000, Windows 11 22621.2134, Nvidia Driver Version 536.23
I would love a solution to this. I don't wish to be dramatic, but it is preventing me from playing DCS at framerates greater than 60. There experience is very jarring to my eyes, looking something akin to 30fps, irrespective of the high framerate.
Happy to troubleshoot with you.
Regards,
Hugh
At framerates other than 60 or 120 fps, there is rhythmic stuttering when looking around with TrackIR in DCS World 2.8. When not looking around using TrackIR, and instead looking around with hat switches, or mouse look, the image is perfectly smooth.
The cause:
Unknown. TrackIR has a polling rate of 120hz, which is a likely contributor to this issue, but does not explain why some titles are affected and others are not, or to varying degrees. For instance, Enabling vsync in Microsoft Flight Simulator or IL2 Great Battles, resolves this issue, or minimizes its effect to a point where it is unnoticeable. In DCS, prior to version 2.8, there was no need to enable vsync, or limit framerate, but the user could Alt+Enter to enter apparent "Exclusive Fullscreen", resolving this issue. I can confirm Alt+Enter does not fix the issue anymore, it is prevalent in both exclusive fullscreen and fullscreen.
This is a camera position issue as far as I can tell, in that the position of the camera is not updating linearly on each frame, there is a jump on certain frames and those certain frames appear to be in sequence - e.g. frame 5, 10, 15, 20. I have a video later in this post displaying this. I could deduce that some games are using a form of smoothing to predict the camera position, and bypass any erroneous position data, but I am speculating.
Research:
I first reported on this issue in 2016, in the following thread on this forum:
https://forums.naturalpoint.com/viewtopic.php?t=13991
There have been many more forum discussions since then, here are two recent ones:
https://forum.dcs.world/topic/267346-tr ... tc-solved/
https://forum.dcs.world/topic/325383-tr ... servation/
This is a difficult issue to reproduce - it requires testers run a monitor at a refresh rate greater than 60hz (more common today), and of course, capturing a video will not show the issue clearly, more often than not because the clip has been recorded at less than the in-game framerate, or framerate has been restricted by the upload platform. The only way to see it is frame-by-frame. Below is a video I have captured showing the issue, frame-by-frame.
https://youtu.be/AWHxhHa4ejI
What is noticeable, is the fact there are no real hitches or pauses in the game, but rather every five frames there is a jump or acceleration in the camera position, evident in the relative motion of the P-51 when moving from frames 4-5, 9-10, 14-15, and 19-20, respectively. Then, the very next frame (6, 11, 16, 21) shows less acceleration than all other frames. So the result is quite interesting. If we focus on one instance of stutter (frame 5), we see accelerated movement on frame 5, reduced movement on frame 6, and by frame 7 we see the expected position of the camera, which is to say, the acceleration on frame 5 and deceleration on frame 6 nullifies any gain in camera movement. This makes sense, because if the camera position simply accelerated every 5 frames, we would see a divergence of the input (head tracking) and output (camera movement), so the two must cancel out. But why is there a 'spike' in camera position every five frames?! That is the question, as removing the acceleration and deceleration between frame 5 and 6 would create linearity of movement through the frames, and stutter would be resolved.
Troubleshooting:
There is no apparent hardware issue, all indicator lights are working on the device, and there is nothing to suggest an IR issue. I have also been fortunate to borrow a friend's TrackIR5 and reproduce the issue with their device, and in multiple environments / lighting conditions.
I have lodged a ticket with Eagle Dynamics who provide the following analysis:
Your problem is not related to the fact that enter exclusive full screen was removed from DCS, since other users and our testers do not experience problems with TrackIR stuttering.This may be due to some third party software or TrackIR settings.
They expanded on troublshooting, asking me to cull a considerable number of background processes, as well as establish a new admin account on Windows. Neither of those provided any change to the issue, which isn't surprising, because I don't believe this is a 'stuttering' issue in the traditional sense. The game itself is not stuttering, it is the camera movement, or the camera movement is inducing stuttering.
I have been fortunate to build a new computer, and have been able to reproduce this issue on both old and new systems indicated below:
System 1: 4790k, 1080Ti, 16GB DDR3 1600, Windows 10 19045.3086, Nvidia Driver Version 536.23
System 2: 7800X3D, 4090, 32GB DDR5 6000, Windows 11 22621.2134, Nvidia Driver Version 536.23
I would love a solution to this. I don't wish to be dramatic, but it is preventing me from playing DCS at framerates greater than 60. There experience is very jarring to my eyes, looking something akin to 30fps, irrespective of the high framerate.
Happy to troubleshoot with you.
Regards,
Hugh