full control over fading density of a grid, post-sim

[ttdww]

This is a carry-over from the radial ground dust thread we're dealing with. Since this sim is mostly controlled by density and velocities pushing straight upward, thought I might try to sim it in overlapping sections.

Any thoughts on how I could control how to blend them together at the vertical edges? The standard 40% fade-off is not enough control and I don't want to fade the top/bottom. I'd almost need a mappable method in Z-direction.

F*me has the fade daemon which resolves this and per-sim box. Is this possible using some combination of Vray/PFD? Thanks!

[Svetlin.Nikolov]

Hey, you could map the volume shader's Smoke Opacity with a gradient texture in Object XYZ space (using the Modulate box), if the fade options are not flexible enough. However, V-Ray's Phoenix shader will blend the overlapping volumes fine in any render mode, so maybe give it a shot without any fade-out - if the smoke density is high enough or depending on the camera angle, it might not be an issue at all.

[ttdww]

Cool will just give it a go and try out no fade. The last time I did a high detail missile trail I had to fade every single overlap with a script ;D but I did have noise in that case whereas most velocity is upwards in this dust sim. That wasn't in PFD btw.

If I end up going with the gradient, how do I control the UV position? Does it just default to the extents of the sim box size? Is it also easy to fade in X and Y direction? (asking for the future). Sorry if this is a bit newbie-ish. Haven't done any post-sim fades in PFD yet.

[Svetlin.Nikolov]

Yup - in Obejct XYZ mapping it uses the grid box (and will stretch together with the box in case of adaptive grid, so watch out). In World XYZ it would be fixed in space, but it needs some trial and error to set up until you find the right offset and scale

[ttdww]

Awesome - that helps a lot. Thx.

[ttdww]

What about fading the top of a smoke sim in the X or Y direction. Would that just be a matter of changing XY to VW or WU, or using rotation? Sorry machines tied up - planning for when I get to this.

[Svetlin.Nikolov]

Either should work, you can also multiply several textures, though the more textures you use, the slower the performance...

[ttdww]

Perfect - will give it a shot. Have 2 sims done and can't wait to blend them. Even 'if' I go with one larger sim using the speed-up, this will be great to know for other cases where density fading is needed.

[ttdww]

Ok new question - realizing I can do a nice radial gradient fade-off of this cut-up sim (it's 6 sections). Is there a way to map all my sim boxes so that they all more easily share a common center point of the gradient radial ramp? So this would mean setting the gradient ramp to 'planar mapping' and relying on some form of UV map.. added to the sim boxes? Or can I only use XYZ object and World?

[Svetlin.Nikolov]

Hmm, can you show me how are you splitting the space in 6 sections?

[ttdww]

Sure thing. Here are 2 sims done and detail reduced so you can see the radial shape I'd like to fade it to. I was going to do it with the ground plane, but fading it will look better - and beats roto'ing it as it grows ;D

I'd like the center point of the gradient radial ramp to be at the top middle-ish of the center sim of the 2 I've done. I could probably crunch the math to get the uv offset to where it should be for each of the 6, however an overall global uv would be more efficient.

I chose 6 since it gave me less than a sim-night each at low spacing.

[ttdww]

here's a couple test renders so you can see how it's coming together.

[ttdww]

post-sim color mod - this is going to work well.

[Joelaff]

Could you use a world space map? Or a Distance blend or falloff from object ?

[ttdww]

Thx very much for the ideas. Worldspace is def. a last resort but that would work. Interesting idea with falloff - will give that a shot.