Started by Matt, June 13, 2018, 07:18:11 am
Quote from: pokoy on June 21, 2018, 07:27:24 amFYI - there's also a velocity channel included in the file (also in the first vdb file you posted) having the same channel name.
QuoteThe strange thing is that the Arnold volume shader has a transparency parameter which is set to 0.3679 (0-1 space). With this value, density has to be at 0.18. The shader doesn't accept more than 2 decimal places so who knows what exact value needs to be, but it looks like a good match. Disabling transparency will result in a black cloud and shadow, so I've left this value where it was.I thought it's meant to produce 0.5 in sRGB, but it seems to be an arbitrary value, if it's linear it should be 0,2176 to produce 0.5 in sRGB, if it's in 2.2 gamma it should be 0.7297 to produce 0.5 in linear space - no clue what the reasoning is behind this as a standard value.
QuoteScattering/GIThis is where transparency controls everything again. If I want the cloud to look good I need to increase the value but then the shadow will be a lot lighter than in TG's example. The GI result further down is what comes out when rendered with the same shader that matches the diffuse/shadow render.I guess it all comes down to how volumetrics work in Arnold, there's no simple way to achieve the same results for diffuse/shadow and GI.General light intensity has to be around 1.68 to produce a close match to TG's exposure/brightness.
Quote from: paq on June 21, 2018, 12:10:05 pmHere's a test using the density channel as emitter (thanks to Démian from Isotropix). It's allready better than the default smoke look I had, but clouds are now self emitter @Matt isn't any other possible data that you could generate in the .vdb that "we' could use to enhance the lack of inside scattering in our test ? Quoting a reply from mdkay (Clarisse forum)how does the shader (sic) fake the extra lightboost..The volume shader in clarisse can mimic these phenomena with the scatter value for forward or backward transmission. But that value is static through the entire medium unless a property is provided to multiply it with.Something like a SDF value which gives a value how close a point is to the surface of the vdb ...Something Matt sure can add..otherwise a run with Houdini would help as well.
Quote from: pokoy on June 22, 2018, 02:24:53 pmI finished a batch of renders from 3dsmax with Corona (v2 release candidate 4)Density had to be set to 2.5 to match TGs output. With GI enabled, I finally had some success to get something that looks close to TG. Corona simulates anisotropic scattering, by using values from 0.6 to 0.85 (forward scaterring) it finally looked more like clouds instead of a white or gray mass. It was surprising to see that not even 10 GI bounces were enough to get a convincing look so I left it the default limit which is 25. A render with constant scattering direction at 0.825 is attached.
QuoteUsing the vdb density channel as scattering input instead of constant and a custom gradient on the output curve I came very close to the GI render from TG but it took to long to render, I'll try to play around with the options another time.
Quote from: Matt on June 22, 2018, 08:29:32 pmIn the past, Terragen faked the internal scattering according to the density function, and we had "fake internal scattering" parameters to control that. But that was in Cloud Layer V2. Now in Cloud Layer V3 and Easy Cloud it isn't faked, it's calculated by scattering rays through the voxels using principles from physically based rendering, although I do cache a few things and take some shortcuts to make it faster than a properly unbiased method. A good physically based volume shader should be able to do the same, if it has a good phase function and enough scattering events (or bounces). Terragen's cloud shader is optimised to approximate hundreds of scatters within the same volume, but has a limited number of bounces between separate cloud layers (or between cloud layers and surfaces) where this optimisation isn't used (although this might be added in future).
Quote from: pokoy on July 04, 2018, 11:34:50 amI had some free time, here's the progression from 0.0 to 0.99 for scattering direction. It's interesting how much this affects the cloud's look.
Quote from: ajcgi on July 04, 2018, 12:20:33 pmQuote from: pokoy on July 04, 2018, 11:34:50 amI had some free time, here's the progression from 0.0 to 0.99 for scattering direction. It's interesting how much this affects the cloud's look.Is this animated? It's static on my work machine at least. Chrome and IE. Win7