Further fluid experiments + material experiments (Patreon)

This is a longer, more "technical" related post so strap in!

Fluids

Thinking about fluids kept bothering me, like there *has* to be a way to get something nice. This is what I had previously:

It doesn't look awful, and there's some aspects I like (like the smoothness of the larger jets of fluid) but the issue is the unnatural rippling and pieces of liquid flying/falling off. This is pretty low viscosity (I think like, 0.02? But it doesn't actually mean anything in reality, the numbers in the simulator aren't based on real-life measurements). Also, the domain is lower resolution- semi viscous fluid at a relatively low res looks not bad for the most part, in some cases it's pretty good. But since the idea is that there's fluid emitting pretty much the entire animation, this ends up not looking so good.

There's some things you can do to help with the weird holes, like enabling sheeting, but it still doesn't help the thinness of the liquid.

You can increase the resolution, but then the smoothness starts to go away. Viscosity started to look like the wrong answer, so I tried using surface tension (see the gif at the top of the post!). I've tried using it before, but it seemed to not help much. But then I thought about using more resolution with the surface tension. This is all using a domain with a voxel count of like 6.4ish million voxels.

It helps a lot, but still the fluid isn't as "stringy" as it should be. The surface tension helps to make the fluid have the string-like effect you'd want to see in large, furry volumes of [j]i[zz] but the fluid is too "light." What I think would look nice is this sort of stringiness, but more gooey/goopy. It looks nice in stills though! You can see on the screen the previous type of fluid per frame.

Like here's a good example of what I mean:

The fluids in what's on the screen is fluid with higher viscosity. The fluid from his butt has no viscosity- I'm thinking that the viscosity has a bigger influence on the weight of the fluid (like, how it reacts to it's emission velocity) than I originally though. So, I think fluid with *some* viscosity and *some* surface tension is the trick. As of now, I want to see how a sort of high viscosity fluid looks with surface tension. The results so far:

This is certainly more like it, if you ask me! It might be too thick, but this is the kind of stringy-ness I've been wanting. Like at the end, that band of liquid starting to goop of the bulbous part of the bag- looks quite nice. I also added more friction to the pastry bag and the dragon body, which I think does something (but it's hard to tell what kind of effect it has).

I dunno though, this might be look, depending on how the rest of this test turns out. I think it's fitting that the fluid is more thick, almost like a thin, smooth icing (since the idea is that it's filling for donuts and unicorn baby makin fluid would be smooth, sweet and birthday cake flavored)

Material stuff

This is an idea I had a few months ago, like if you could add some volumetrics to the fluid, it would really help with making something that's convincing and stylized. If you've ever seen real [se]me[n], it comes (no pun intended) in a variety of styles. Sometimes, it can be very thick, very rope like. Sometimes, it's thinner, more clear. But the issue with rendering this kind of fluid is that it's not entirely opaque or transparent. It's full of all kind of biology stuff that causes light to bounce around, it's "cloud" is a way you could describe it.

I'm more of a fan of thinner, more see-through style fluid, but this technique makes it possible to make a variety of styles of reproductive fluid. This is using the "mesh to volume" modifier that you can use on an empty volume object:

I gave the volume a pastel rainbow kind of look using some noise and a gradient image, to make it more magical since it is supposed to be unicorn baby batter. Here are the layers to it all- the pastry bag has it's own volume, as does the fluid.

Still need to mess around with this some more, but this is a lot closer to a good looking fluid shader of this kind of fluid. Volumes have a big advantage- the "denser" and object is, the more light scatters inside of it (the pastry bag is much denser than the fluid, so the volume looks more solid). If there's a large amount of liquid, the volume helps to express that, as opposed to using just alpha stuff.

The fluid mesh has a shiny, liquid-y material with some alpha trickery using layer weight and ambient occlusion nodes, as sort of the "shell" of the liquid.

 The downside is that the volume should be pretty high resolution, which can be slow, but you can turn it off when you don't have to see it.

I also did the soft body stuff for this, I don't remember if those were in the last post, but I'm quite happy with how they turned out! (in the attachment)