X-Plane Beta and Vulkan: A few personal observations

  1. The Vulkan API provides a significant boost in performance

  2. In certain situations, Vulkan API can decrease the overall image quality

  3. Vulkan API in its current implementation is not better than running OpenGL.

No doubt the Vulkan mode provides a significant FPS/smoothness increase. Where I was getting 30-40 FPS over crowded areas like LAX, Vulkan API can keep it will over the 4k 60fps threshold.

HOWEVER: I did encounter a massive drawback, and I hope it is merely related to beta testing, but if you have 8gbs of VRAM, you will not be able to run maximum object settings in crowded places without the ground textures/buildings looking like it reverted to Xplane 9.

The way the new API handles texture loading is voodoo magic to me, but essentially it loads the textures onto the GPU, filling up your VRAM for smoother flying. Sounds great, works great too as long you are in relatively open areas. Flying over big cities or crowded areas brings on the problems. As you fly, the game manages how much VRAM is currently being used. If the game requests more VRAM than you have available, it lowers the quality (resolution) of the textures to fit the available amount. If you look in the Log.txt you will see lines that tell you something like:

0:03:35.388 E/TEX: Target scale moved to 2.000000

The target scale goes from like 2 to 16. 16 being the highest I believe.

So the problem is the game runs smoother and faster, but you cannot raise the settings to take advantage of the newly found headroom because you are hard limited to your VRAM amount. For the 1% of people that own 2080ti’s with 11gb of VRAM, you may not notice this. But for me with 8GB, I may run 20-30fps slower on OGL, but the image is vastly improved. I can run High (HDR) effects, Maximum objects and get about 40FPS over a big city and look great in OGL, but in Vulkan I’ll get 60+ FPS but the texture quality is greatly reduced.

The solution: Limit objects to High if you have 8gb of ram and want to use Vulkan. Personally, I prefer to run Max Settings on 11.41 with lower FPS. Looks a lot better.

"But I run Vulkan with maximum objects and I dont have this problem!!!"
You may not experience the blurry textures if you:
A)have 11gb of VRAM (might still occur, I can’t test)
B)Aren’t flying over Crowded areas
C)you are using a light aircraft in regards to textures. Laminar C172 etc.
D)Aren’t running in 4k.

Easy way to test is try to fly the Zibo 737 4k Texture version on Vulkan out of LAX w/ maximum objects. It crashes every time for me becuase it says I dont have enough VRAM. Load it up in 11.41 openGL, and its buttery smooth.

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This paragraph…

Ya know…when I viewed the video that what’s-his-name did about how great Vulkan was going to be I thought of something like this. Sure a flight sim needs things like asphalt runway textures …and I guess preloading stuff like that into the GPU memory saves time…but what about concrete runways, macadam runways, steel mat runways, gravel runways, dirt runways, grass runways, coral runways, sand runways? … and what about other areas where you don’t have a lot of similar textures?


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Sounds like what I experienced, more or less.

I have an nVidia 1080 w/8Gb.

I was strictly testing in VR however. So I didn’t notice a loss in texture quality; there might have been, but it wasn’t enough to draw my attention to it.

In the end I went with High, sometimes even Medium, objects as I do most of my flying ‘in the bush’ and in VR I’m trying to get it as smooth as possible.

FWIW, full-screen with my 4K monitor is about 2x the FPS I get in VR. Just as a quick test.

Clouds are what really kill the FPS for me. I’m not using any addons. Note that I have been using a cloud DataRef tweak that adds 10-20% FPS.

Let me dig it up here…standby…

Ok, using FlyWithLua, this script runs each session:

set(“sim/private/controls/clouds/cloud_shadow_lighten_ratio”, 0.85)
set(“sim/private/controls/clouds/first_res_3d”, 3.0)

The first stops the clouds from ‘flickering’, the second uses more simple clouds. But again, in VR I don’t see a huge difference visually from the default (I know that a lot people don’t care for the default clouds in the first place). The default value for the first_res_3d is 0.0, not 3.0.

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The problem with using FPS as the benchmark in Vulkan mode is that it will give you arbitrarily high FPS, especially when tweaking settings related to GPU vram, because it just lightens the texture load. So I may be getting 80fps, but the textures are a blurry mess. It gives you this false headroom where I think most of us say “Ok, I’m running at 90FPS, so I can now increase my graphics settings until it dips down to 45-60 or whatever is tolerable.”

Hopefully this helps someone dial in their settings. I think we all want to have the best looking and best performing experience for our respective setups and preferences.

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I’ve noticed this in VR; 45 FPS sometimes is smooth and sometimes it isn’t. It’s kinda odd. And sometimes it depends on where I’m looking; looking out the left window, under the wing, is often choppy (not horrible, just noticeable), out the front or right window is smooth. Really odd.

I’ll have to pay closer attention to the textures next time.

Beta I guess.

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Yes VR is its own beast and also throws in a couple other variables. I have had good results with the Rift S and using the OVR add on to lock the FPS to 40 and use 1.5 super sampling. Others have had success disabling ASW, but I think it was smoother with it on. If you don’t have an oculus, there may be similar addons for other devices.

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Yep . Definitely factoring vram into the next gen gpu purchase decision . Fella on YT who prefers his Reverb for X-plane is using a Rift-S post-Vulkan .

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I think the 3000 series is rumored to have up to 20gb of VRam. Should be able to handle Vulkan nicely!

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We’ll see…that was the rumour earlier in the year (and had me excited) . But the latest has down-sized it considerably . It’s all scuttlebutt for now…only time will tell .

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Do we have an indicator (beyond blurriness) that Vulkan is starting to diminish the graphics level? It would be kind of cool to see it on screen, like the little blue/light blue motion reprojection indicator that was (still is?) in WMR. With an indicator, we could chose Vulkan or OGL based on the anticipated area we might be flying in. Although clouds and visibility are probably the big variable there…

I think there is a performance debug tool. If you look in your log.txt files, you can where the “heap” over steps it’s VRAM boundary’s and the target is lowered.

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And by the way…I’ve seen the blurring of the panel textures right when I jump into the sim, and after a few seconds…I presume Vulkan is loading the airport area and the surrounding graphics, the panel textures snap into clarity. Kinda freaks me out when it does it because I’m like “wait…were the panels supposed to be blurry like that…I can’t remember…nahhhhhhh…”

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its really easy to test. Just load into LAX and look at the terminal/gate/carts around you. If they are clear, your good to go. Crank the settings up and watch them go back in time… if you have a Ti, it may not happen. Running with high vs maximum objects is a trade off you’ll have to consider if you’ve got 8gb of ram. I noticed on the notes for the next update there is mentioning of tuning this process, I think (hope) the final product will be much more efficient. I’m pretty sure the intent is to blur textures further away and keep the nearest ones sharp as VRAM usuage increases.

Interesting observations, @Gunnyhighway.
As a VR user with 11GB VRAM I have indeed only seen the upsides of Vulkan.
I agree with your thoughts about this being early days and that improvements will happen. LR have a good track record for squeezing the code for performance.
That said I guess we also have to view Vulkan in the context of future proofing. It is obviously an API written for modern and future hardware.

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Yeah…my 2080ti and 32GB of RAM seem to be treating me pretty right.

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An interesting read…although I haven’t understood most of it. What I do understand is that I should wait until this is out of Beta and I don’t need to tweak anything (which I haven’t a clue how to do) before “upgrading”.

In the meantime…back to DCS. :sunglasses:

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Which is also in beta :grin:


Why yes it is! :grin: And they keep breaking things that used to work. But that’s OK, because it is a Beta that I can understand and don’t have to mess with strange VRAM settings…or get the hamsters to run faster on their little wheels…or whatnot. :rofl:


I understand where you are coming from, but honestly if you fire up the Xplane beta and dont change any settings from what you have now (except for ticking the Vulkan box), you probably won’t notice anything other than higher FPS. I didn’t run into these issues until I started trying to increase the graphics settings to take advantage of the perceived headroom in FPS.

But it really is better to just wait on these things. DCS beta is a different story…


Oh , i don’t know …sometimes i think the most realistic thing about DCS is the maintenance hours/flying hours ratio :slight_smile:

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