smoke pops from small surfaces

[TomGore]

How to avoid of sudden plumes of smoke emited from lets say small rocks falling from destroyed cliff? when smoke emission in source is 0.5 (quite dense smoke) a smoke appears suddenly over stone's surface and then smoke behaves correctly. But how to eliminate this one-frame appearance? Is there an option to put this earliest smoke into transparency over "voxel age" as we can do with particles? I dont want to make other source object squeezed inside original rocks to hide this sudden pops of smoke. I would like to make it smooth.

[Svetlin.Nikolov]

In case you have non-constant emission from a constant source, then this needs to be investigated, and not worked around. Are absolutely certain that all geometry is closed and there are no holes, flipped normals or overlapping faces?

[TomGore]

this is from cached geometry (point cache, xmesh, alembic, whatever) - i dont see any technical possibility for smoke to show up on the surface without sudden density value. How do you think it works in standard situation? If you create a cylinder emiting smoke, then smoke with a set "smoke value" like 0,5 and discharge velocity > 0 will appear suddenly in the surface-voxel with 0.5 smoke density by default, right? Only making voxels smaller than pixel can reduce visual poping because then early smoke voxels are so small you dont see the exact time and place of poping.

[Svetlin.Nikolov]

Ahhh, I see - you want the smoke to gradually fade in until it reaches full opacity. This would work if the emitter geometry is non-solid and the source emits in Brush or Inject mode, combined with motion velocity in the source enabled and set to 1, so the geometry would involve the smoke in its movement correctly. I think this would be the cleanest and easiest solution currently with the grid solver. Using surface force, the smoke and all channels in general are born at their final value, so in future versions I'd like to add the ability to independently control both the increasing of grid values by sources, no matter what the emit mode is, as well as to be able to direct the surface force vector not just along the normals, but in a custom direction too.

[TomGore]

Okay - brush mode. But will the smoke collide with other stones when whole cache object is not solid? No. so what would be the solution then? Scene is in slow motion so popping is very visible as the only rapid thing in the super fluid animation.

[Svetlin.Nikolov]

You should enable motion velocity in the brush source exactly in order for the non-solid objects to affect the smoke as if they were solid. The effect would not be completely identical, but the non-solids would still contribute velocity and you'll be able to regulate it with the per-object motion velocity multiplier as well.

[Svetlin.Nikolov]

But indeed, if the entire geometry is cached in one piece, I am not sure if per-vertex velocity would be able to translate to motion velocity...

[TomGore]

Okay, I will try and I guess it may be the solution. I didn't understand brush mode differences, I guess. Too bad I didnt know it before making this sim, it would save me a lot of effort to hide sources' surfaces: https://youtu.be/Vg9D7g631PE

[Svetlin.Nikolov]

Hmm, wouldn't a discharge modifier based on velocity also help in this setup? You could map the smoke amount depending on the vertex speed and this way smoke could emit in varying quantity per geometry fragment and the simulation would look more natural and diverse.

I'm a bit worried about the puffs of smoke appearing here and there though.

[TomGore]

But how to do that? how to make a vertex velocity (indeed stored in caches) influence smoke emission values?

[Svetlin.Nikolov]

Hey,

Here is an example: disch_mod_smoke.zip

https://www.youtube.com/watch?v=5F_buBsg-kE

The motion velocity is highly exaggerated so there would be visible effect from the falling particles. You could also modify the discharge modifier curve in order to get different emission for different speeds.

Would this work for your setup?

[TomGore]

Yeah, this works great for rayfire-simulated falling rocks and bricks sending dust into air, like here for example: https://www.youtube.com/watch?v=dh4r-gHdyPU - imagine this sequence 5 times slower. Then smoke suddenly showing on the debris edges would be annoying and unrealistic. Your idea seems to be okay for this kind of destruction. Or perhaps there are better approaches?

[Svetlin.Nikolov]

For now this is it, but I hope we'll be able to implement the alternatives we spoke about in the beginning of the thread and then there will be more ways to approach it.

Cheers!

[TomGore]

Btw. When we can expect some build with added some minor features? I am hungry for them.

[Svetlin.Nikolov]

Me too, but it's gonna take some time to finish some other tasks first