Transparency doesn't work with cloudy volume scatter?





  • @joker a potential problem with props containing a volumetric shader, is that scaling the prop requires inversely scaling the density, since the density is in geometry units, not worldspace units.

    Here's my comment from a Volumetric Shader thread on this forum:

    Absence of scaling is an important requirement for the density settings of volumetric absorption and scattering in SuperFly. My experiments with standard props scaled up to large volumes to enclose the camera and scene objects has required equivalent (and logically appropriate) scaling down of density settings (to maintain their mesh-relative units). I suspect there may be some fixed precision operations involving density, which are intended to speed up the calculation of volumetric effects during renders, beyond what can be achieved by using floating point operations. The side-effect of using fixed precision is that tiny density scales can underflow to zero, thus reducing the possible effects to either on, but too much (totally opaque) or off, as I have observed in such experiments.

    Without object scaling, changes to volumetric effects are easily seen with small value changes to the density inputs from their default of 1. If one needs to scale a volumetric prop to match a scene, the simplest way to revert to unitary scales is to open the grouping tool, select all the facets of the scaled prop (or actor) and spawn a new prop, then delete the original, scaled prop.

    I think you may also need to bump up your Transmission Bounces, perhaps.



  • @anomalaus Thank you for your answer, but I don't understand what and how it's to change.

    But maby anybody can change this example file in this way, that the transparent plane is not visible anymore in this cloudy fog cube?

    https://drive.google.com/file/d/153BihsTj2H02ZZlYyzeoMlvCnC-s8tN4/view?usp=sharing

    0_1558335967479_plane2.PNG



  • I can reproduce the issue using the provided test scene. No matter what i use: PoserSurface or CyclesRoot node, CPU, GPU, BPT on or off. As soon as the volume is modulated i get the trans issue.



  • @nagra_00_ Thank you for reproducing this issue. I tried so many things but nothing worked to solve this problem with trans in modulted volume scatter.

    Maybe anybody will find a solution? Or maby this is only solvable by the software developers?



  • @joker Does this happen with cloud modulation only or does any modulation like e.g. a simple density gradient has the same problem?



  • @nagra_00_ The issue is with any kind of modulation the densitiy of the fog

    0_1558348003047_Illustration.jpg



  • @joker Ganz schlecht :( Looks to me as if this could be fixed by the devs only.



  • @joker Looks like i found a solution:

    0_1558350193645_vol_trans.jpg

    The setup looks strange but seems to work.



  • @nagra_00_ Ok, forget it does not work...



  • @nagra_00_ Yes, that's what I am thinking also. The devs can fix this issue only. But the question is, will this happen anytime?

    Atmosphere effects are very important in my eyes. It makes a scene much more idyllic. I try to communicate this bug a long time here but nobody finds a solution.