David I forgot when exactly I got it :/ the propeller came in the last couple of hours (I wasn't doing anything active, but I got some rep and badges this evening)

@NicolaSap seems to be the share link for the propeller hat.

@NicolaSap Nice! That translucency looks yummy ;)

I'm surprised so many people were against it, seeing as in the past interest was quite high..

(even @David suggested contests of some kind)

@NicolaSap @David is a hat monster

@AnindoGhosh Ask away!

I'm not sure if you meant asking in chat or on the main site, but the answer is the same either way

As you can see, response time in chat isn't terribly fast (especially at this time of day)

On the main site there's a good chance your question may have already been answered, so do have look around in the meantime

@gandalf3 I'm not fussed about response time. :-)

What is your question? Perhaps I can help

@gandalf3 I've already searched the main site, but perhaps what I'm trying to do is too new, so not many questions on the subject. Also, since my question is related to how to do something in Blender that can be done in Keyshot, I'm not sure what kind of anti-Keyshot hostility I might find on the main site - Back on my home site, EESE, hostility against Arduino questions can be lethal :-D

I see

I think particles probably are the best way to go about it

It might be a bit of a hack, but perhaps using a slightly shrunken duplicate of the mesh as a particle emitter?

Now, why do I want to try this in Blender instead of Keyshot? (a) because my access to KeyShot is on a friend's computer, I don't own it yet. (b) I want to animate the flakes to move upward, and randomly (but not all at the same height) blink out of existence as the ramp goes below a threshold. I figure that Blender is better equipped for such math.

@gandalf3 Wait, how do I make the particles remain contained within a complex shape after emission, other than using a "do not render" invisible container? From your suggestion, it appears that is possible.

Ah, I hadn't seen the bit about them floating upwards yet

I guess my question is not ideally suited for the main site, as it is becoming what is called a "unicorn question" on EESE, as I go along: The nature of the question is changing as your answers expand my mind :-)

I think you'll be able to get them to stay inside with a collision physics modifier

@gandalf3 Umm collision physics requires my collision wall thickness to be greater than maximum particle dimensions, unless I'm misreading something. Right?

So the thin sharp bottom part of that skirt shape, for instance, would be devoid of any particles.

I'm really sorry. I might be wasting your time on an unsolvable problem, and that is not my intention.

I'm just testing some things out :)

@AnindoGhosh I think you're right. I thought particles used their size in collisions but perhaps not

@gandalf3 I suspect the 0:0:0 point of each particle is tested against the collision object's envelope, so Monte Carlo dictates that some cases will spuriously find the particle to be outside, if the particle is big enough - after which the particle floats off unconstrained :-D

Quite so

I can't think of a tool which will give a perfectly suitable slightly-smaller envelope to act as a collider, but if that's the shape I don't think it would be too hard to do manually

@gandalf3 Oh, no, that isn't the shape I am working towards - My upload was a far simpler model a friend made. I'm working on shapes like partly hollow star shapes (the pendant necklace on that model).

@gandalf3 I am toying with a slightly different solution: The do-not-render collision object can be an outer shell to my desired shape: Basically a surface extrusion from all faces, of dimension slightly bigger than particle size. That should allow successful collision detection, while allowing the particles to exploit the entire target object volume.

Ideally, I would be looking for the exact same mechanism Keyshot uses, i.e. a duplication of a shape, then replacing the material with a volumetric geometry transform into particles of some other material and shape. Is there some such approach available in Blender?

@AnindoGhosh You can have object(s) rendered at the location of each particle, if that's what you mean?

@gandalf3 Yes, that is so, but that's where our discussion started: How do we constrain those particles to be conforming to a certain outer geometry, without adding a collision geometry / containing shell of a certain minimum thickness.

The more complex the original shape, the more complicated it becomes to create the containing shell for the collision physics, if I am analyzing the problem correctly.

For full collision you might be able to use rigid body physics, but I feel it may be way too expensive for the number of particles you probably want

@AnindoGhosh I'm afraid I can't readily think of a better approach than the particle system. It wouldn't hurt to ask on the main site anyway (if you haven't already) in case someone clever than me has some inspiration. If you need it to be exact you may be able to replicate Keyshot's behavior with some python scripting (or even something like the animation nodes addon), but it that route will very likely take quite a fair bit more effort.

As far as particle systems and collision shapes go, the shrink/fatten tool (Alt+S in edit mode), The displacement modifier (without a texture, it can be used to move faces along their normals just like the shrink/fatten tool), and the solidify modifier are probably your best friends for creating a proper collision envelope.

Here's one I made while testing things out, albeit with the simpler shape: pasteall.org/blend/index.php?id=50888 Perhaps that gives you some idea if you can meet your requirements by fudging it or not. Best of luck!

@gandalf3 Thanks! I'm going to fudge around a bit with "fatten"