Fluid Controller Project Help

Hey All!

So I am working on a music video that I directed for a band involving a select number of VFX shots. The concept is that these shadowy creatures (literally shadows on the wall) are harassing this woman in a dark, creepy house. I’m going to be doing the compositing work in After Effects since I don’t know how to use Blender’s compositor yet, but I am trying to use Blender’s physics sims to create the creature plates.

Basically, I’m working on a shot where the woman passes by a wall and we see one of the shadows following after her. I want it to seem very fluid. The idea is that this formless fluid-like shadow follows her and mid-shot, composes itself into the shape of a snarling mouth chasing after her, then decomposes back into the formless fluid like shadow we saw before as it exits frame.

At first I tinkered a lot with the smoke sim and got some pretty awesome looking smoke, however I couldn’t figure out a way to control the smoke’s shape in a way that I could animate it.

Then I realized the fluid sim had a controller object. My idea was to model the shape of the creature’s head, animated it with a very basic armature, then set the rendering opacity to 0 so that when the fluid grabbed onto the control object, it would seem as if it was forming itself into the shape of that object on its own.

Doing this however, I ran into some issues:

  1. Attraction: The fluid controller doesn’t act like a magnet. It doesn’t attract the fluid to it, just makes the fluid stick once it touches it. I realize this now from doing a lot of research online, but it does make it more challenging since I now have to get the fluid to collide appropriately.

  2. Detail: It’s hard to adjust how closely the fluid sticks to the form. Particularly, it tends to fill up the eye socket I created for the mock head I modeled (a much better model to be used instead once I have the concept working correctly). Any help on the detail front would be awesome!

  3. Fluid Control: The fluid will stick to the object momentarily before dispersing from the object, almost as if being pushed away from it. I still haven’t figured out how to keep this from happening and it’s really killing the project to be honest. If I can figure out how to keep the fluid stuck to the object, particular while the object is moving and being animated, then it defeats what I’m trying to do. This is primarily where I could use some advice as I don’t know why the sim is behaving this way.

  4. Baking: Most of the time the sim bakes just fine, however sometimes when it’s baking, I see the baking progress bar at the top of the window for a split second before it disappears. When that happens, the sim only bakes for a few sims. I can’t tell whether the bake is still happening and Blender just isn’t showing me it is, or if the bake has crashed. When I try to scrub the time line, I can see a few frames of the fluid mesh before it reverts back to the original setup. Maybe it’s just an extremely long sim and I have to let it be over night? It’s hard to tell since their’s no progress bar.

Any help or advice would be awesome! I’m attaching the blend file for people to see what I’m talking about. Bear in mind, this is just me messing around and testing to see how to get it all working, so there’s not too much to see yet, but you should be able to see what’s happening.



Creature EFfect Shot.blend (494 KB)

Control object, when splashed or dipped through fluid, the volume holds onto the fluid. You shouldn’t use identical object for control and fluid. That is why you are seeing funny behavior by fluid.

Control objects Attraction Force needs to be way down for it not to fill the eye cavity. I tried Strength of .2 and Radius of .75 but it is still filling up. It needs to be lower.

By the way you do need to set animation time for control object, and domain. You have Scene set at 24 fps. That makes 10 sec run of 240 frames. You need to set that on Time Line. Then set Control and Domain time to Start at 0 sec, and End at 10 sec. Don’t ask me why they all are preset with different number!

Alternative method for this animation is to use shadow object with deform modifier. All you do is to slide the deform texture over the shadow object for it to modulate its form. Shadow object can be made to morph in to different shape with shape key as well.

Thanks Ridix!

So let me make sure I understand correctly. Does the control object “fill” with the fluid or does it only hold the fluid to the surface of its mesh? I.E. Does it act as a magnet or a container? Also, I’m guessing my fluid object must be larger than the control object then?

That’s a great idea with the deform texture and the shape keys. My only concern would be that I’m trying to get this creature to appear as if it’s composing itself from a lot of disparate fluid elements, then decompose itself as well. Is this possible with shape keys?

Also, any thoughts on my baking issue? I can’t tell whether the sim is actually baking or not since the progress bar disappears and there doesn’t seem to be any progress in the viewer beyond just one or two frames. I can’t figure out what’s going on. This only happens after I’ve baked the sim a few times.