Fake volumetrics shading issues galore! ;)

[skinnytorus]

Hey guys,

I'm trying to fake volumetrics the old school way by repeating a bunch of planes and applying a 3d noise texture to the resulting stack. But there's a couple of issues I've encountered:

1) It works only if the camera is above the ground. A look from below ruins the shading completely (even if the surface is lit from below). Why is that?

2) Is there a way to constrain all the repeated planes to always look at the camera, but the noise stay in world coordinate space? This might solve the first issue IMHO.

I've attached my test compo. Any ideas?

Volumetrics1.compo (16.0 KB)

Thank you,
Skinny

[francis]

I didn't open the compo yet, but here a few hints that could help:
1) Isn't this simply due to the "Side" option in the renderer that should be configured to "Both"?
2) Instead of working with instantiated planes, I'd directly try with particle sprites: indeed sprites are camera-facing by default
3) For the overall (world-space) noise, the "3D discard" nearly does the job. Unfortunately, I'd to slightly modify the shader to obtain the right result:

What's missing is a "3D Alpha" that uses a 3D Mask to multiply the alpha channel of what's rendered. Would you like to have this new effect?

[francis]

I just added it, that was an easy one

[s21]

[skinnytorus]

Hey, guys.

@francis

1) Isn't this simply due to the "Side" option in the renderer that should be configured to "Both"?

No. Of course the Sides parameter is set to Both. I'm lame in some areas of cg, but not this lame in this instance Disabling the Depth Buffer test for the Surface shader partially solves the problem, but the layers become sorted incorrectly and it breaks the illusion.

2) Instead of working with instantiated planes, I'd directly try with particle sprites: indeed sprites are camera-facing by default

Not sure about using Sprites in terms of performance. My quick test of your 'sprite ice cream' scene in the new beta shows occasional fps drops to 24-25 when rotating the camera around the 'volume'. Perhaps it's due to the size of the sprites that gets bigger due to the point size modifier. I need more time to play with the scene. Will check back later.

3) For the overall (world-space) noise, the "3D discard" nearly does the job. Unfortunately, I'd to slightly modify the shader to obtain the right result:

Ok for that. Perhaps you might want to make your modification an option - just not to break the compatibility with older scenes. Or you've already achieved what you wanted that in your new 3D alpha mask and no modification to the 3D discard mask is needed?

What's missing is a "3D Alpha" that uses a 3D Mask to multiply the alpha channel of what's rendered. Would you like to have this new effect?

Yes. Looks pretty handy. Thank you very much!

But anyway, so far I find working with vertex colors (in my example I use the Colorize points Modifier + a stack of hi-res mesh planes) much more efficient in terms of performance compared to using the 3d masks on the diffuse channel directly. Smode somehow seems to handle vertex colors better on my system (Nvidia GTX1000 + 6 core i7).

In fact, I'm trying to find ways to achieve the effect explained in this article: https://80.lv/articles/working-on-volumetric-clouds-in-ue4/. Watching the video in the beginning of the article will help you get a better picture of the result that I'm after. Casting shadows within the volume seems to be a major problem though. Perhaps we'll need a volume grid to handle that...

@s21
Thanks for the tip, mate! It's much better like that, but as I said above, disabling depth testing breaks the illusion. Any other thoughts?

Skinny

[skinnytorus]

Hey guys,

As promised, here is my test compo for you to play with. The "Instanced planes + vertex color" method clearly beats all the other ones in terms of fps.

Volume Tests 1.compo (67.9 KB)

Skinny

[francis]

Hello @skinnytorus,

Just to mention, but otherwise you have this technique too:

[skinnytorus]

Hey, @francis

Thanks. Tried that already. It's good, but something is missing. The look I'm after is this:

I wonder if such volume shading is possible in Smode? Looks cool, doesn't it?

Skinny

[francis]

Sure it looks good!
Note that there are some very similar shader toy shaders that can be ported to Smode. We should definitively add some presets to the custom shaders to show this...

[skinnytorus]

Great! Thank you! By the way, a Special Layer cloud preset could come in handy as well. Countless users would be really delighted to have the ability to create volumetric realtime cloudscapes interacting with scene camera out of the box.

Skinny

[francis]

Hello Guys,

Here is a port from IQ's famous volumetric cloud shader (https://www.shadertoy.com/view/XslGRr):

VolumetricCloud.compo (31.1 KB)

Can't exactly figure out why, but it doesn't look as shiny as the original.
The good news however is that this type of shaders immediately works with special cameras:

[Walter_heen]

Hello!
Here is a way to create a kind of 3D cloud.

3D clouds.compo (31.5 KB)

[skinnytorus]

@francis

Not bad. Quilez's works are fantastic, but this one has been around for quite a while already.
IMO clouds need more resolution.

If I were you, sitting down to volumetric shader presets, I would start with simple shapes such as these:

https://www.shadertoy.com/view/MljXDw and https://www.shadertoy.com/view/lss3zr.

Conditions to meet:
1) full interaction with camera moves
2) exposed parameters for noise, color, cloud xyz dimensions, cloud position in world space, scattering/absorbtion amount/color, light position/direction/color.
3) should be usable with depth pass to ensure interaction with the rest of the scene.
4) should be usable with projection camera/light for casting shadows on geometry in the scene.

In other words, individual clouds should serve simple construction bricks for building a cloudscape from scratch.

Then I would switch to more complex scenarios:
https://www.shadertoy.com/view/ll2SWd (it's the best I could find for the clouds from above)
https://www.shadertoy.com/view/XtBXDw (a classic volumetric cloud background - a MUST for working with set extensions). The more parameters we can expose the better. I don't know however if the conditions for simple volumetrics as described above are fully applicable in these cases, but the more we can squeeze out of those shaders, the better.

So... What's your idea?

Skinny

[skinnytorus]

Hi, @Walter_heen.

Of course, sprites can be used to achieve that effect, and the results may be pretty decent, but without a 2nd independent UV layer for sprites based on the cloud's bounding box it's kinda hard to apply gradients to sprite textures to fake the light scattering effect.

Here. Take a look at how I approach sprite-based clouds. Looks pretty good, but however I try there's always something wrong about the shading.

cloud2.compo.zip (29.4 KB)