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Messages - somedoggy

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[Max] I need help! / Re: Need to change account email.
« on: 2017-07-02, 02:46:27 »
Sorry, I should have specified that I don't mean for the forums but for the account I login to on the main site. I have already changed it for the forums which did not affect the email I sign in with on the main page, or get billing statements to.

[Max] I need help! / Need to change account email.
« on: 2017-07-01, 04:33:49 »
Is there any way I can do this?

Yikes. I guess for the most accurate results you can always bool a small sphere at the camera source, but that's not the most flexible workflow.

This information makes sense of similar problems I've had with participating media in Corona when playing with planet renderings, and a few other points of volumetric weirdness I've encountered.

I was testing light shafts with volumetrics and when unable to get anything working I searched online. Although I found a workaround, this seems to be a pretty strange issue, and for any scenario other than a static camera this technique does not work at all.

At first I was using a global volume, but switched to a box to allow more light to get in initially. This didn't work, and the workaround I found is to move the volumetrics box just outside the camera. For some reason this works perfectly, and I'm guessing booleaning a tiny sphere out right at the camera would work too.

Camera is inside fog volume:

Volume mesh is edited so camera is just outside, but the rest of the volume is kept as identical as possible.

An observer should not need to be in a different participating media (or here vacuum) to see light shafts inside the media.

Caustics and corona do not play nicely, at least not without some compositing/separate passes. I would avoid trying to chasing realism to the nth degree and go with a more artistic "it looks right" approach. I'm sure others will be able to chime in on how to setup the caustic passes correctly.
Thanks for the reply! While it is generally good advice to strive for good art over pure physical accuracy, with these works the intention is to push accuracy.

Before posting I looked some into compositing Bidir/VCM techniques other shave shared as well as general caustic setup techniques. There's nothing really wrong with my setup (hence being a bug report thread). Bidir/VCM is unsuitable for my projects considering its limitations.

I have done more tests and found that the sky only illuminates the room "faster" because of contributing a lot of light over the entire area of the glass. The sky is properly interacting with caustics. In my last test I compared a sun light with a HDR map that has a single bright dot of almost exactly the same size/intensity. I found no difference here.

This reveals the issue is that relatively small lights sources of any kind will not clean up reasonably using caustics (even using only a sun light). Even when allowing it to run for a long enough time that the light pools on the floor, that illumination is not then bounced off the spot despite it clearly being the most important source of indirect illumination.

as far as I remember, light translation through a flat refractive object with caustic enabled is a known problem since long time ago.
but I failed to point which bug report, you can search it again on older bug report threads
It would be great to see this get some much needed attention as it's a hard limit for producing plenty of effects. When writing the OP I looked through pages and pages of search results for "caustic"/"caustics" and you're right that it's a long standing problem. Nearly 300 posts across the forum if you tally it naively. I do appreciate the complexity of the issue though. I hope to see some strides in the future! This is my most wanted improvement.

Hello! While working on a series of pieces attempting to push realism as far as possible, I have come to realize that caustic materials behave strangely. I've set up a test scenario for this problem.

The setup here is a barebones room/glass setup with the glass intersecting into the room box on all sides, allowing no leaking as far as I understand. The light sources are the Corona Sun and Sky combo, though I have also tried a Corona light which produces the same issue but renders faster. In the leftmost image you can see a typical rendering with caustics disabled on the glass material. As expected the bounce off the ground has provided the majority of illumination to the room.

The right two are the same render but show a clear oddity in how Corona is rendering: no light from the sun has managed to illuminate the room after contacting the floor. Confusingly, the light from the sky environment manages to start illuminating the room immediately. Even rendering with the sky as the only light source produces (slightly) different results when toggling caustics, which makes me believe that the sky also interacts with them. This "lagging" behind of actual light sources vs the sky environment is perplexing.

What can be done about this? I'm currently cheesing the render in my actual scene to get my desired effect, but in the future I have more caustic heavy work planned that would require correct rendering. I greatly appreciate any insights that could be offered into why this happens and what can be done.

This was done in a new scene with 1.5 hotfix 2, in Max 2017. All renderer settings other than MSI and max ray depth are at their defaults.

Thanks for reading!

Thanks! I'll give that a try :)


Could you share your setup? I cannot replicate your projection.

Hi! I'm trying to use a light source to project an image into my scene. You can see in this picture that while my light has a directionality of 1 and the source image is high quality, the projection on the wall is blurry far beyond expectation.

Pushing the light source closer to the wall produces sharper images, but this does not make sense for lights with a directionality of 1 which intuitively should act like a perfect laser (projecting a perfectly sharp image through a vacuum, forever, and not obeying inverse square). In reality a laser can produce a sharper images even at this distance (a few meters) and, obviously, such an ideal scenario is not even required to produce sharp images. You can see this for yourself in movie theaters.

This is making it hard to model a virtual projector, something I need for my scene which pushes for purely practical effects in a digital environment. Has anyone been able to accomplish something like this? Any info or pointers on errors I may have made?

Apologies if this is a dupe of previous threads. A cursory search yielded nothing and I have spent most of my time looking at the documentation.

I'd like to hear more about the mention that the high roughness ranges aren't physically plausible for GGX.

For any BRDF I know of. Designing a BRDF function with reasonable shape that is physically correct (meaning properly normalized, symmetrical), flexible (going from mirror to diffuse), and efficient (meaning it can be sampled reasonably closely and efficiently evaluated) is actually pretty hard.

What is usually done is some kind of approximation that is "close enough" on the physical correctness side. It usually works well for nearly-mirror surfaces (it is much easier to design a function that looks almost-mirror), but when going more diffuse, the whole thing just goes bonkers. This was the case with previous BRDFs in Corona, which is why the minimal glossiness was cut off a bit. I dont know how badly GGX blows up on near-diffuse end though. Not blowing up in vray does not mean there are no problems with GGX generally, they could have done further research, some masking hacks, or it could blow up in a way that is usually not visible (as did some previous Corona BRDFs)
I remember reading at first they had a problem with it blowing out for rough surfaces, and if I remember correctly it was due to their shadowing-masking function. This paper outlines height-correlated shadowing and masking, which is a pretty good solution to balance that out:
Page 75 Eq. 99
I believe the best form though is Equation 101 on the next page. Since I'm not sure how the sampling or brdf in Corona work in code I can't really speak on being properly normalized otherwise. Could be a number of things. It would be really cool to have references for these types things to ensure people are getting the best results from their workflows. Also I wanted to pitch an idea, if it hasn't already been implemented. There are normalized functions out there for burley diffuse which would be a cool brdf option for Corona :) When balanced properly the resulting soft brightening of a rough surface's diffuse is very nice.

Edit: I found their post

+1 to increasing the roughness range. To add to this, and something I mentioned on Polycount, I noticed that displacement was causing surfaces to appear overly glossy for me. Could just be a perceptual thing, but it seemed to intense to just be that. I'll try to put together a test based off what I was doing before, but I'm on the free alpha version of Corona now so it may be different.

I'd like to hear more about the mention that the high roughness ranges aren't physically plausible for GGX.

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