Prop animations are the lens flares of aircraft models (was: Prop animation makes horizon and clouds wobble in VR)



  • (skip to this post if you don't care about the VR-specific parts of this thread)

    When I look at the horizon or clouds in front of the aircraft through the rotating prop on a screen, I can see that they're wobbling very slightly. It's a subtle effect, and it wouldn't bother me at all.

    But when I put on my VR headset, this effect seems a lot more pronounced. In specific situations (I think depending on cloud formation, distance, and lighting), it turns everything in front of me into a breathing, wriggling, pumping organism.

    I'm not sure whether this is just the result of a subtle effect on screen being scaled up to a VR fov, or if there's additional post-processing that's causing the effect to be much more pronounced in VR.

    Other prop animations in MFS (e.g. the one used for the default C172) don't show this effect.

    I'm using a Valve Index, Motion Smoothing and Legacy Reprojection are disabled.

    I'm curious to hear from other VR pilots: do you experience this issue with your headset? Does it bother you?

    Cheers,
    Marc



  • I did some flights with other prop planes and paid more attention to the wobbling. While the effect is present with other prop animations as well, it's usually hardly noticeable.

    I also found that, in the P28R, the effect depends massively on the circumstances. When I wrote the post above, I was under the impression of a flight in dusk with heavy clouds ahead, which were bathed in red sunlight with cloud layers creating high contrast. That's when the pumping clouds and the wobbling horizon gets really bad.

    I guess I'll try to avoid this scenario when flying the Arrow.

    Again, I have no idea what's actually causing the issue, whether it's a property of the Arrow prop animation, or something that is happening elsewhere between the sim and the VR headset.



  • It's probably related to the issue with the beacon light discussed here earlier, which stems from a larger issue with the MSFS graphics engine that causes weird behavior around transparent objects. And since the prop is technically just a transparent circle, that would likely affect this too



  • Not sure if that's the same issue. Either way, there must be ways to mitigate the problem or it would affect the props of all prop planes, right?



  • Hello, it is because of the motion reprojection.

    I can see this in my HP Reverb G2 when the reprojection is on in the OpenXR settings. Once disabled, it goes away (together with the reprojection, of course 🙂 ).

    This unwanted effect can be mitigated by increased transparency of the prop disk texture. This will make the prop disk barely visible on the other hand.



  • @apollon01 said in Prop animation makes horizon and clouds wobble in VR:

    it is because of the motion reprojection.

    As I wrote: "Motion Smoothing and Legacy Reprojection are disabled."
    I'm not aware of any other SteamVR settings that would influence this.

    Also, this effect in MFS looks distinctly different from reprojection artefacts caused by prop animations in P3D or XP. These reprojection artefacts usually look "jittery" – the reprojection picks what it considers an object behind the prop, guesses a vector (wrongly, because it doesn't understand the prop animation), predicts a motion, the image is distorted before it "snaps back" (like a flag in strong wind) when the application is done with the next "real" frame.

    In my original post, I mentioned it's like looking at a "breathing, wriggling, pumping organism", and, yes, it feels more organic simply because the effect is looping back and forth. Imagine, instead of the prop, a round lens that introduces some form of distortion (like the ones used to correct for astigmatism) turning in front of the plane at 3-4 rpm. That's probably the best way I can describe it.

    I know jack shit about computer graphics. I have no idea how the effect of a rotating prop is realized, except that it's not done by rotating the images of static propeller blades at 2000 rpm. 😄

    If part of the prop animation was a layer with varying transparency that "moved" at a rate of a few rpm, I would bet it's related to my problem. If not… then I have no idea what's happening and why.



  • My VR headset is being replaced because of a hardware issue, so I'm spending some time flying "flat".

    So, here's what I learned about the issue: a lot of prop animations look basically like this:

    propanim.png

    Zones of varying transparency approximate propeller blades with motion blur. The animations are then rotated at different speeds. E.g. the prop animation in the C172 moves faster, in the Arrow, it moves slower.

    Look through either prop at something high contrast in the MFS world. If you look closely, you can see the different zones of transparency slightly distorting high-contrast transitions. If you're in a C172 it's a high-frequency distortion (which I find less distracting), in the Arrow, with it's slower moving prop animation, it's the wobbling I'm going on about.

    And now imagine having a lot of contrast ahead of you, like multi-layer cloud formations in certain light conditions. Suddenly the prop animation creates a lot of perceived "motion" in front of you, because all the areas of high contrast are affected. Finally, imagine blowing up the picture on your screen so much that it covers your whole field-of-view (as VR does). You can imagine that the "slight" wobbling can be very pronounced and very distracting.

    I accept that this is a problem with the MFS graphics engine, but it's exaggerated by the design of the Arrow prop animation.

    Here's a blasphemous thought:

    Prop animations with motion-blurred blades are the lens flares of aircraft models.

    What do I mean by that? Look at a running ventilation fan. What do you see? Something that looks like single fan blades with motion blur? Or do you see a partially transparent disc, possibly with concentric circles if the fans are not unicolor, perhaps with highlights where light is reflected by the fan blades?

    Of course you can take photographs or videos that look exactly like what we see in the sim. But our eyes don't have a shutter speed that "resonates" with the fan rotation, right? Just like our eyes don't have lenses that would create a lens flare -- so some of us turn lens flare off in all our games and sims because, while lense flares make for beautiful screenshots, they're signaling "this isn't real, you're not really there, this is something captured through a camera lens." You might not have noticed, but your brain did.

    While I think I understand why prop animations are done this way -- simmers are used to it, most of us see props more often in film and video than in real life, and it can provide some nice visual feedback when changing the prop rpm -- I feel it's not only a poor design choice because of the idiosyncrasies of the Asobo graphics engine related to transparency, but also because it's not what we would see with our own eyes in real life.

    I'm certain you've seen the "bent prop blades" effect in GoPro footage on Youtube. Would you accept a prop animation in MFS that looked like this? It's just as close to the first-hand experience as the motion-blurred blades. 😉

    I think this is what prop animations should basically look like:

    propanim2.png

    It's darker in the center because there's less space between the prop blades at their base than at their tips.

    Remember looking at your fan? If you see light reflecting off it, the reflection isn't rotating with the fan, it isn't moving based on the RPM, it only moves when you change your viewpoint or the position of the light source relative to the fan. This would be how a prop animation would behave in a perfect world, but I don't know if that is even possible with the tech we have in MFS.

    Convince me I'm wrong. It wouldn't be the first time. 😄