Quote from: Matt on August 30, 2013, 08:50:04 AM
Very interesting blinkfrog! You clearly understand the problem.
Hello Matt, this is a honor for me.
Quote from: Matt on August 30, 2013, 08:50:04 AM
To my eye, your view from above the clouds is doing a pretty good job, although it's not quite right yet. There are compromises and plenty of edge cases that just don't look right unless we literally brute-force sample every path. Or are you actually doing that?
Of course there are plenty of fakes. Indeed I started to implement some things by brute forcing it, by tracing the some of the most probable photon paths in the cloud, to understand the overall principle. Next I simplified the paths, also added some volume estimation, and next I eliminated the direct tracing and simplified the estimation to make calculations faster. Now it is pixel-based (I mean, not GI-based, but calculated for every pixel for every tracing step, that is slow) cloud volume estimation.
Quote from: Matt on August 30, 2013, 08:50:04 AM
What sorts of rendering times are you getting?
Well... For the quality of last two images the rendering process is somewhere about 2 hours at the 3.3 GHz i5. Too many, I know. There is a space for optimization, I have some ideas. But I currently prefer work at algorithms, than at optimization. I need to learn many other things as it is. Constantly reinventing the wheels, because I haven't any experience at 3DCG.
As for that scattering phenomenon at wide angles (I call it "curve scattering" because of curve scattering paths idea laid in the core) I can make it GI-based that can greatly speed up things. But it can lead to great detail loss, that is critical for high density clouds. I tryed it before, and it wasn't good, but my old GI-system was very slow and crude (so I usually used it at low resolution) with ugly interpolation. May be with my current reworked GI it would be better. But my GI is still far from TG or Vue in terms of smoothness and speed.
Quote from: Matt on August 30, 2013, 08:50:04 AM
QuoteWell, it is like I need to work more at the internal scattering. But may be the cloud just isn't designed well? May be it too dense?
It may be the scattering isn't right, or the cloud density isn't realistic, or both. But nature creates clouds with such incredible variety, and there are probably many different density profiles that all look "real". I would expect that we should have some freedom to create many different density models and still make them look realistic if the lighting simulation is good enough. So I think the scattering probably needs improvement. However, your first cloud image might look more convincing if the fractal did not have such sharp valleys. The unrealistic fractal might be distracting us from really being able to judge the realism of the scattering. It looks like it's generally doing the right thing, even if there's still something unnatural about the falloff and it's hard to pinpoint what it is.
Yes, of course scattering needs more work. And cloud design too. Currently I get cumulus billows by abs() of perlin noise (shaped for linear distribution), may be it is worth to round the zero mirroring.
As for clouds design, it is my favorite thing, so creative! All this multifractality with some tweaks and height-dependent behaviour changing is like magic. But it isn't so handy currently because of hardcoded functions, so I currently am starting to thinking out my shader system. So many wheels to reinvent.
Quote from: Matt on August 30, 2013, 08:50:04 AM
I'll be interested to see how this progresses
Well, I can't promise fast progress.
After all, it currently at hobby status, and I working already about 3 years with great breaks (sometimes several months). I thought about commercial project, but it is hard. I need to learn so many things, and even if I invest my time and money to it there is no sense to make such project when at the market such brilliant products as TG or Vue are presented.
But I like that I worked at it. I learned so many interesting things, and also now I am seeing at the sky different to earlier. I can spend many time looking at the clouds, and now I see all the beauty in the nature multiple light scattering. There are no people understanding me.
They just can't notice nothing special in the light scattering, they can just say "nice shape, it's like rabbit".
P. S. Also there are some other ideas that I like in my engine. For example, multiple scattering in the sky. While it needs tweaking, it featuring more or less realistic rayleigh multiple scattering, and I got nice solution for sunset time. I mean, just 1st order rayleigh (and mie) scattering is too dark at sunset, multiple scattering can greatly illuminate sunset sky, but it is more gray than blue. So I implemented atmospheric ozone imitation which influence is very prominent at sunset (when the sun is low or below the horizon) and makes blue colours more juicy. But there is also a problem of HDR to LDR conversion, and my current solution distort the colors.
Here is a picture of sunset, the sun is below the horizon.