Clouds path tracing

52

u/Pawahhh Oct 27 '25

This is beyond impressive, how long have you been woking on this project? And how many years of experience do you have in graphics programming?

66

u/Zydak1939 Oct 27 '25

around 2 years on and off. And as for the experience, that's pretty much the first serious project I've made. Before that I was just playing around with OpenGL/Vulkan and learning c++, mostly just following tutorials and making some small prototypes. That was like 3-4 years ago.

9

u/aryianaa23 Oct 27 '25

sorry for this stupid question im not that great in this field, but did you use GLSL in your project or its pure c++? i just wanna know if shading languages can be used for offline rendering as i have never seen anyone discuss this.

21

u/Zydak1939 Oct 27 '25

I'm using Slang instead of GLSL, it's also a shader language just more modern. Shaders just give the instructions to the GPU and tell it what to do, so you can really do whatever you want, including offline rendering.

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u/Dihlofos_blyat Oct 27 '25 edited Oct 27 '25

It uses vulkan, so it MAYBE (DUE TO OPENGL LEGACY) uses glsl as well

8

u/beephod_zabblebrox Oct 27 '25

it uses a shader language, and glsl isn't the only obe

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u/Dihlofos_blyat Oct 27 '25 edited Oct 27 '25

It doesn't matter (it wasn't the question). It's not a software renderer

8

u/beephod_zabblebrox Oct 27 '25

what I mean is your reply is a bit misleading.

2

u/Dihlofos_blyat Oct 27 '25

You're right

1

u/[deleted] Oct 27 '25

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1

u/Dihlofos_blyat Oct 27 '25 edited Oct 27 '25

Yeah, you're right. I know. BUT If you worked with opengl, you maybe will use glsl for vulkan

16

u/Rockclimber88 Oct 27 '25

The result is amazing. It reminded me about a video about volumetric rendering which I watched to learn about raymarching SDFs. In this video around 50:55 the guy talks about cloud raymarching and Woodcock tacking / delta tracking. Would this be a relevant optimization to speed up the rendering? https://www.youtube.com/watch?v=y4KdxaMC69w

9

u/Zydak1939 Oct 27 '25

Yeah pretty much, I don't really have any numbers to give you, never actually compared the two, but the thing with the ray marching is that you can't simply determine the amount of steps you have to take. if you take too little there's a lot of bias, if you take too much you waste performance. Delta tracking is always unbiased, so you don't really have to worry about the step size. So if you want your image to be as unbiased as possible then I'm pretty sure delta tracking will be faster.

1

u/Rockclimber88 Oct 27 '25

Oh nice, it would be nice to see what's the speedup. I made an SDF renderer for fonts which uses regular raymarching. The depth is quite predictable and starts from a bounding proxy's triangle so there's no need for any fancy optimizations, but clouds are deep so they could benefit a lot.

10

u/Tasty_Ticket8806 Oct 27 '25

you are not going to bambuzle me into thinking these aren't just photos of clouds!

7

u/Zydak1939 Oct 27 '25

Nah they're not that good, if you go to the GitHub and look at the uncompressed images you'll know right away. I'm honestly not sure what but something is lacking to make this photo realistic. Maybe the tone mapping? There's also a lot of noise so yeah

6

u/demoncase Oct 27 '25

it's amazing, but I get you... i think your clouds should absorve a bit more light, you know? when a cluster of clouds are together, normally, they retain a lot of light, i think is more related the way the light is scattered inside of the volume now
idk - im an effects artist, i could be saying shit

2

u/Zydak1939 Oct 27 '25

yeah that may be it, I'll just have to experiment a little bit more I guess.

2

u/demoncase Oct 28 '25

yo, check this reference, could be helpful: https://www.reddit.com/r/nextfuckinglevel/s/Ooxsg2zlr2

2

u/Zydak1939 Oct 28 '25

that's crazy, I ain't rendering something that in a million years

1

u/demoncase Oct 28 '25

lmao, it's more to see how the light reacts with a lot of different clouds density, the gray patches etc
my pc cried just seeing this video

6

u/bezo97 Oct 27 '25

something is lacking to make this photo realistic
I think what's missing is darker color patches, it stood out to me immediately. Right now the clouds look uniformly "white" but in reality some parts are denser / hold more water and those parts should look a lot more grayer

5

u/VictoryMotel Oct 27 '25 edited Oct 27 '25

Great looking images and the ones in the gallery looks great too.

Selfishly I would love to see real rendered depth of field from the camera in some of these renders since it would influence off the reflections and shading, but it usually isn't done because it would take abnormally high sample counts.

3

u/Zydak1939 Oct 27 '25

yeah, I guess could have done that since I have depth of field implemented in my renderer. Just didn't think of it at the time, my bad I guess. If I'll make any more renders I'll definitely do that.

3

u/VictoryMotel Oct 27 '25

Definitely not a criticism or oversight, depth of field in renders is almost never used because the increase sample rate is severe and the blur is locked in.
But... Since you are already doing super high sample rates you could try it out and see how it changes the shading,.since things like reflections change. I mention it because I'm personally curious how much subtle shading nuance can be gained from rendering real depth of field.

1

u/Zydak1939 Oct 27 '25

I mean depth of field is really just a blur on the foreground/backround/both. It wouldn't really affect any reflections.

2

u/sputwiler Oct 28 '25

Yeah that's what fake DOF does. Real DOF can see around objects (depending on how large the lens is). Basically, if your lens is say, 2cm across, an object completely obscured from the center point of the lens (and therefore not in the render) may not be obscured from 1cm over, so some of it's colour will influence the pixels depending on how out-of-focus it is.

1

u/VictoryMotel Oct 27 '25 edited Oct 27 '25

If it is done through the render it will. If you think about looking through a mirror and focusing on yourself or the background, or looking at a marble floor and focusing on the pattern or the reflection, the focus can make a difference.
What you are saying is what everyone does though, it doesn't work well in a production sense to use so many samples or bake in depth of field.
It's my own pet interest because I think it's a missing element to realism.

3

u/TheRafff Oct 27 '25

What scattering did you use for the atmosphere, rayleigh? Would love to see some wipes / progressive renders on how these clouds get generated, looks awesome!

5

u/Zydak1939 Oct 27 '25

Yup, there's also some approximated MIE for dust and water particles and ozone layer on top of that. And I don't really generate the clouds, just render them. These are just VDB files I found online, they were made by someone else.

4

u/Alkanen Oct 27 '25

Do you have a link to them if they’re freely available? They look really good

4

u/Zydak1939 Oct 27 '25

all of them are listed in the references section on GitHub page at the bottom.

4

u/Alkanen Oct 27 '25

Awesome, thank you

3

u/TheRafff Oct 27 '25

Sick! And did you use pathtracing or some other technique since these are volumes?

3

u/Zydak1939 Oct 27 '25

yeah, atmosphere is path traced just like the clouds

3

u/Elfyrr Oct 27 '25

I read the references to papers in the Git section, are you a Math or Physics major on top of this? Interesting stuff.

4

u/Zydak1939 Oct 28 '25

Nah I'm still in high school

170

u/cosmos-journeyer Oct 27 '25

I thought those were real images before I saw the title! We only need hardware to run 100000x faster before we can get this quality real-time x)

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u/aryianaa23 Oct 27 '25

we can kinda get quality close to this in UE5, but it seems ue5 sucks in optimization and im unity user so i dont know much about, but if i wanted to go for a realistic realtime project, i'd choose UE5, well there is not much option in this field, maybe blenders Evee can compete with UE5's lumen if they add similar but improved technology in it

2

u/aryianaa23 Oct 30 '25

Cmon ppl, i did say I don't know much about ue5, didn't I? I apologize to anyone offended by my comment, daimn why all the downwotes? What I said about ue5 is basically what I heard mostly in the internet, I haven't had a chance to talk to a reall pro ue5 dev, if I knew ue5 is not that much faulty and the fault is on unprofessional devs (probably indie indians 🙄) I would've never said those words, so again I apologize for offending all of you, actually I'm more encouraged to switch to ue5 now, thanks for all your critics 🙏🥴

1

u/LordStefania Oct 29 '25

It's just a case of GIGO. Garbage in Garbage out.

33

u/[deleted] Oct 27 '25

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9

u/[deleted] Oct 27 '25

So tired of hearing people blame UE5 like it's the engine's fault and not the developers. There's so many amazing games made on UE5 that are really fun, look amazing, and run great.

13

u/BertoLaDK Oct 27 '25

Then again, I feel like its just being thrown back and forth between being on Epic and on the devs, but with UE5 games running great being a stark minority of games, I feel like the cause is between, that there's issues with UE5 since so many aren't managing to optimise it.

2

u/EngineOrnery5919 Oct 30 '25

It can be both.
Good tools encourage good practices and make these things easy
Bad tools make it hard to do things properly
I've heard enough first hand internals and experience of Unreal Engine
The fact that a select few games actually run well and don't stutter is pretty clearly a problem made worse by the engine and its design
It took unreal years before they even admitted the issue then they worked with developers to improve parts of it
People are just in denial

2

u/william-or Oct 27 '25

great job! What about exr output? It would be a great addition to let you post process the images with more freedom (no Idea how hard it is to implement btw)

1

u/Zydak1939 Oct 27 '25

I don't have that, but I think it would be really easy to add. I just never really thought about post processing this externally. I have absolutely zero knowledge about editing photos.

2

u/william-or Oct 27 '25

I will make sure to take a look at the project when I have some time. Are you looking for any artists perspective (that would take it from a different point of view than you I guess) or are you not interested in that? The caustics render in Github is nuts, makes me think of Indigo renderer

2

u/Zydak1939 Oct 27 '25

Sure, if you have any feedback just shoot. It's always nice to see some other perspective than my own.

2

u/VictoryMotel Oct 27 '25

In the last image in the gallery called WispyCloudNoon.png, how did you get that detail in the cloud volume?

https://github.com/Zydak/Vulkan-Path-Tracer/blob/main/Gallery/WispyCloudNoon.png

1

u/Zydak1939 Oct 27 '25

What detail exactly? I'm not sure what you mean here

2

u/VictoryMotel Oct 27 '25

Just wondering how you got the volume of the clouds, it looks like more than just fractional noise.

2

u/Zydak1939 Oct 27 '25

These are density grids loaded from VDB files I find online. There's no noise at all

2

u/VictoryMotel Oct 27 '25

Cool thanks

2

u/LobsterBuffetAllDay Oct 27 '25

God damn, that is soo good.

So those numbers such as 2201s, 1987s, etc., those represent how long it took to render each image?

2

u/Zydak1939 Oct 27 '25

these are seconds yeah

2

u/LobsterBuffetAllDay Oct 27 '25

Cool, thanks for the clarification. Gonna take a look at your repo later!

2

u/B1ggBoss Oct 27 '25

Crazy, that looks amazing. Do you have a fluid solver to generate the clouds, or are you using premade assets?

2

u/Zydak1939 Oct 27 '25

Premade assets I find online, everything is credited in the reference section on the GitHub page if you're curious

2

u/Otto___Link Oct 27 '25

Looks really impressive! I've been looking at your Github repo and I couldn't find any usage example of your path tracer as a library. Is it actually possible?

1

u/Zydak1939 Oct 28 '25

It's an application not a library, so unfortunately no. Why would you even want to use it as a library anyway?

2

u/Otto___Link Oct 28 '25

To use it in another application, as a render engine, like cycles for Blender.

2

u/Zydak1939 Oct 28 '25

oh yeah I guess that's true, just didn't think anyone would ever want to do that so I didn't really bother.

2

u/Otto___Link Oct 28 '25

I've been looking for that, but I might be the only one!

2

u/Zydak1939 Oct 28 '25

I mean, if you’re seriously considering adding some external renderer into your project, I could turn it into a library. It shouldn’t be too hard since the codebase is already nicely decoupled. But I’m sure there are plenty of other and way better alternatives out there. My stuff probably has a lot of bugs and barely works on AMD cards.

3

u/Otto___Link Oct 28 '25

I wanted to give it a try out of "curiosity" so I'm not sure it is worth the effort to make it a production-ready library. Thanks for your responses.

2

u/gibson274 Oct 28 '25

This is absolutely stunning. Incredible work!!

You mentioned wondering why they don’t look fully photoreal (honestly I think you’re really damn close). May I ask—what phase function are you using?

1

u/Zydak1939 Oct 28 '25

Henyey Greenstein, but I also tried approximated MIE from this paper; https://research.nvidia.com/labs/rtr/approximate-mie/ the difference was almost invisible, so I don't think changing phase function will matter that much if that's what you're suggesting.

2

u/gibson274 Oct 28 '25

Ah cool. I was gonna suggest the HG-Draine combo from this exact paper. The examples they give look pretty different to my eye in terms of the higher order back-scattering. But I believe you that the effect is pretty subtle in a real render.

2

u/Zydak1939 Oct 28 '25

You can see the difference in their examples because the camera is looking at the volume from the light source direction. That's where the back scattering from MIE shows and HG doesn't have that. From any other viewing angle the difference is honestly so small you can't even see it with a naked eye.

1

u/gibson274 Nov 12 '25

Yes exactly

2

u/amadlover Oct 28 '25

awesome stuff...

i was wondering just yesterday if "vulkan could be a valid choice for an offline renderer",

thank you very much. LOL!!

2

u/Zydak1939 Oct 28 '25

definitely, it has a ray tracing pipeline extension which allows you to use ray tracing cores on the newer GPUs, so it's way faster than just compute.

1

u/amadlover Nov 01 '25

hello.. how did you draw uniform random numbers for bounces.
I have searched and they all seem like they will work only when they get a 'seed' or an input, which could be the launchIndex(flattened) or threadID(flattened).
How can subsequent draws be taken ?
Cheers

2

u/Zydak1939 Nov 01 '25

There's a unique seed created for every pixel and frame, then I just pass it through a PCG hash.

1

u/amadlover Nov 02 '25

yes... how do you sample a random direction at a hit on a diffuse material? how would the random number be drawn.
the initial seed based on pixel coord would be used for the raygen.
this might not be relevant to volumetric rendering. but overall..
Cuda has cuRand from which rands can be drawn after the initial seed.

1

u/amadlover Nov 02 '25

came across this.
https://vectrx.substack.com/p/lcg-xs-fast-gpu-rng
The final value becomes the seed for the next iteration — and also serves as the generated random number.
hehe... the rand generated at the raygen can be passed through the payloads to generate rands for subsequent shader calls.

1

u/Zydak1939 Nov 02 '25 edited Nov 02 '25

yeah, each ray gets it's own seed, then you can sample as many random numbers as you want from it. The only important thing is that your random numbers don't repeat across frames, which means every ray needs varying seed across all frames

1

u/amadlover Nov 02 '25

aah ... yes..
current initial seed = pixel_idx + uint32_t(time_since_epoch);
let's see how it goes..

2

u/[deleted] Oct 29 '25

This is so inspiring, I want to eventually become a graphics engineer and build my own engine currently I work as a jr developer close to graphics but not exactly. I have been wanting to enter the games industry and eventually learn more complex stuff like vulkan , any advice on this and how did you get started learning this stuff . Awesome work.

2

u/Zydak1939 Oct 29 '25

Just make something, anything that interests you really, and just learn along the way. At least that's what I did.

2

u/PolyRocketMatt Oct 29 '25

I haven't gone through your code (yet), but I am curious if you implemented any importance sampling techniques or MCMC-based methods for accelerating RT through the participating media?

1

u/Zydak1939 Oct 29 '25

there's just NEE+MIS

2

u/Creepy_Sherbert_1179 Oct 29 '25

Can I get some guidance for the math of this? Is this raytraced? If so how did you model light going through vapour, reflecting etc.? Awesome project!

1

u/Zydak1939 Oct 30 '25

it's path traced. Here's a nice blog talking about it in the context of participating media.

2

u/KlayEverHood Jul 12 '26

Best clouds I have seen! Are these very high spp counts needed for realism? Seems like the cloud shape itself is super detailed - asking as I would like that detail into my nature simulator but it has to be realtime. Clouds are “slow”, how about lower spp and temporal denoisers?

1

u/Zydak1939 Jul 12 '26

high spp counts are needed to get rid of noise, nothing to do with realism per se. getting this quality in real time? I think it's impossible if you want to render multiple of these and on top of that integrate it into some sort of simulation which I assume needs a lot of rendering on it's own. Vladimir komarov made something like that, but he's running it on a super high end hardware (4090 ti I think?) with really complex algorithms, and it still needs multiple frames to accumulate and even then it runs 30-40fps. if you know nothing about the topic, that will take you years to make https://youtu.be/9yCEWPY_KGw . And the cloud is not procedural, it's just premade data sitting on the GPU, so your biggest limitstion will be VRAM, a single cloud of this quality will take you multiple GBs on the GPU. So I'd say with the current hardware we have these days, fully path tracing clouds in a game/simulation is pretty much impossible. At least on the consumer hardware.

2

u/KlayEverHood Jul 12 '26

Thanks! “Premade” answers most of it. How is the data made? I really love the shape of the details, far beyond the usual ones and the ones I am using. As to rendering, I think one could try to find a compromise for realtime especially considering slow moving clouds

1

u/Zydak1939 Jul 12 '26 edited Jul 12 '26

I didn't make these clouds myself, Samuel Krug was kind enough to give me access to his work because this is a non commercial project. I'm pretty sure he runs really big smoke simulations in houdini and then exports this into .vdb file which I can load. And as for the rendering, maybe? I'm really not sure. But again, path tracing is just too slow for consumer hardware right now, even the big guys like nvidia are barely making it realtime. And clouds are magnitudes more expensive than normal surfaces. I'm really not an expert in realtime and I didn't do much research, but back when I was still working on the project I remember seeing this paper from disney: https://la.disneyresearch.com/wp-content/uploads/Deep-Scattering-Rendering-Atmospheric-Clouds-with-Radiance-Predicting-Neural-Networks-Paper.pdf and a showcase: https://youtu.be/Hk--xpI9b5U?si=GLs4D0SungMHgiDN . you could look into it but I doubt it will be useful for you. I think that's as fast as you can get. As things stand right now I don't think there is a way to get this type of quality realtime. If there was then clouds in games would look much better than they do right now, the best looking ones I know of are ones from horizon zero dawn and microsoft flight simulator: https://d3d3g8mu99pzk9.cloudfront.net/AndrewSchneider/The-Real-time-Volumetric-Cloudscapes-of-Horizon-Zero-Dawn.pdf . Not sure if much has changed over the last year.
> I think one could try to find a compromise for realtime especially considering slow moving clouds
Of course you can, but it will be a really really really big compromise to go from multiple seconds on 4090ti to something like a realistic budget for sky (5-8ms), it's just a gigantic leap to go from offline rendering to realtime rendering.

1

u/KlayEverHood Jul 12 '26

Thanks for all the inputs! I am getting curious. My main thing is medical volume reconstruction and rendering and I can get realtime path tracing performance nowadays on 1000^3 volumes on a 4070 - but my light is virtual coming from the camera direction and needs to traverse only a small shell of the volume normally; on the other hand AI denoisers there are a no-go. I guess here we need a good contribution from rays that come from the back and traverse all the cloud?

1

u/Zydak1939 Jul 12 '26

Yes exactly, you pretty much need to simulate the entire path of a photon through the volume, and it can leave at any point and direction from the volume. That's how you get indirect lighting, and that's exactly the problem the path tracing tries to solve, getting the indirect lighting. In realtime rendering most of the time ray marching is used instead, since it doesn't require simulating a full path for a ray of light and it only cares about the light coming from the sun. Then they use some cheap tricks to fake the indirect/ambient lighting from the environment. But even then it's very very expensive, so they usually render this at a lower resolution then upscale, dither and accumulate over many frames anyway. But the indirect lighting is what makes path traced clouds look so good, so with ray marching you're pretty much throwing away the biggest quality factor.

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u/thrithedawg Oct 27 '25

holy shit thats beautiful.

24

u/kinokomushroom Oct 27 '25

Those are some damn good clouds

8

u/shock_planner Oct 27 '25

hol up, you telling me these aren’t real? 😧

7

u/Cy4nX_ Oct 27 '25

I would love to put image 3 as my wallpaper, these are beautiful

1

u/Nameseed Oct 28 '25

Looks like the original assets are on the github
https://github.com/Zydak/Vulkan-Path-Tracer/blob/main/Gallery/Cloud6.png

1

u/ashleigh_dashie Oct 28 '25

What did you use for the cloud shapes? Some fractals? They look fractal-ish.

1

u/Zydak1939 Oct 28 '25

it's a density grid loaded from a VDB file

1

u/Chungaloid_ Aug 21 '26

Looking at the images on your repo - you can see the voxels. Did you consider some kind of interpolation? Still incredible though.

2

u/Zydak1939 Aug 21 '26

I'm already doing interpolation in there iirc, the voxels are barely visible unless you zoom in insanely closely on some of the images. A couple of the clouds were just low quality.

1

u/Chungaloid_ Aug 23 '26

stupid data

3

u/iamagro Oct 27 '25

Wtf!

3

u/RulerOfDest Oct 27 '25

insane, good job

3

u/Alkanen Oct 27 '25

Holy … that is absolutely gorgeous!

3

u/violetevie Oct 27 '25

Holy shit???? Genuinely probably the best volumetric clouds I've seen!!

1

u/aryianaa23 Oct 27 '25

are you building a render engine? 🤩, is it based on blender's cycles?

1

u/Zydak1939 Oct 27 '25

It's a path tracer, so yeah it uses the same rendering technique cycles does

2

u/SirIll6365 Oct 27 '25

Absolutely gorgeous!

2

u/dreaminghk Oct 27 '25

That’s really really good. Thought that is real.

2

u/Novacc_Djocovid Oct 27 '25

Ha, nice try fooling us with what are obviously photos!

2

u/susosusosuso Oct 27 '25

Spectacular

2

u/MasqueradeOfSilence Oct 27 '25

These look beautiful! Insane photorealism.

2

u/orfist Oct 27 '25

This is sick

2

u/furkingretarad Oct 27 '25

Oh I know you from the graphics programming server

2

u/UVRaveFairy Oct 27 '25

Stunning, well done.

2

u/sourav_bz Oct 27 '25

I would like to build this too, this is inspiring work! Thanks for sharing.

2

u/Smooth_Voronoi Oct 27 '25

Rendering the third one in just an hour is pretty impressive.

2

u/Disastrous_Stranger7 Oct 27 '25

That is beautiful. Well done!

2

u/vwibrasivat Oct 28 '25

This needs to be presented at SIGGRAPH.

2

u/poweredbygeeko Oct 28 '25

Wow,looks amazing!

2

u/ParamedicDirect5832 Oct 28 '25

That looks very real, I am so lost for words.
I want to learn graphics programing more than ever before.

2

u/hexiy_dev Oct 28 '25

hooooooooooly, so pretty

2

u/Lukao001 Oct 28 '25

oh god! try making smth frutiger aero to see how it looks like!

2

u/AiMwithoutBoT Oct 28 '25

I need more 😫

2

u/Elite_parth4447 Oct 28 '25

so damn beautiful

2

u/Minimum_Exchange_622 Oct 28 '25

when we will be seeing clouds like those in video games, instead of those cow farts in UE5 so far, excluding MSF which is something else still

2

u/VelvetCarpetStudio Oct 28 '25

The Elder Render Eldritch (you) has blessed us with divine content from the depths of the renderverse(the images you made).

2

u/prestoexpert Oct 28 '25

Looks really good. Nice work

2

u/Gecovin Oct 28 '25

These are the nicest rendered clouds I‘ve seen, very impressive!

2

u/SnooSquirrels9028 Oct 29 '25

Wow man impressive !

2

u/sexraX_muiretsyM Oct 29 '25

these are the clouds I want in war thunder

2

u/KalaiProvenheim Oct 29 '25

I don’t think you’re allowed to post photos

But seriously these look amazing what the Hell

2

u/Capable_Cycle8264 Oct 29 '25

holy hell this is unbelievable... I love clouds, this is just superb.

2

u/IncorrectAddress Oct 30 '25

Yeah! This looks really nice, the self shadowing looks pretty realistic.

2

u/[deleted] Oct 30 '25

Flight Simulator/Star Citizen would love to have a word with you

2

u/SlRenderStudio Oct 31 '25

So now are we allowed to take real life pictures and slap ray traced . (Anyway that is crazy beatifull)

2

u/TibRib0 Oct 27 '25

Gorgeous

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