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Particle Sprite Z-depth pop

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Eric Barker
Particle Sprite Z-depth pop
on Jan 16, 2019 at 9:42:17 am

For my work, I do a lot of cloud simulations using particle sprites. I've used Particular for about 10 years, and demo'd Superluminal Stardust. One glitch that ALWAYS drives me crazy is that when sprites move in front of each other, they inevitably "pop" in. Since in my case I'm using 2D sprites to replicate 3D objects that take up volume, I'd like some method of crossfading particles when they come close to each other in Z-depth, so they don't make an abrupt cut.

This isn't possible Particular, and I'm not seeing anything better in Stardust. Has ANYONE figured out some trick in making sprites not pop through each other? BTW: often times the sprites are static or slow, and the Z-depth pop comes from a camera move or orbit.

Television Producer
KTVF-11 Fairbanks, Alaska
video.ericbarker.com


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Kalleheikki Kannisto
Re: Particle Sprite Z-depth pop
on Jan 16, 2019 at 10:53:55 am

There are two options in Particular to prevent this. One is making sure that the particles are not so close and do not move in such a way as to cross over each other in the z space. This is what I use mostly. Often works better with the camera set to a tele lens to shorten the apparent distance between the particles .

The other option is turning them into additive blending mode, which is not useful in the case of simulating solid 3D objects with 2D particles.

Stardust can prevent 3D objects (not 2D) going through each other if you use physics collision. I'm pretty sure you could do a in-between solution by using a flattened 3D box (a plane with some thickness to it) and map your texture to it. This way the particles bounce off each other. Not 100% sure if you can retain the sprite-like always-facing-the-camera option when using physics, though, since I haven't attempted this.

I find that Particular is easier to use. Stardust documentation is somewhat incomplete and some of the concepts -- such as what is a physics effect and what isn't -- are inadequately explained. Combining both physical simulation and non-physical effects you can still end up with particles going through each other, as the non-physical effects are essentially post-effects added to physics simulation. But the physics simulation is very nice once you got it working. If you were using actual 3D objects, that would definitely be the way to go.

Kalleheikki Kannisto
Senior Graphic Designer


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Eric Barker
Re: Particle Sprite Z-depth pop
on Jan 16, 2019 at 2:15:20 pm

Thanks for taking the time to respond, unfortunately neither of those techniques are really an option. Doing cloud simulation, I’m typically overlaying hundreds of sprites, and doing camera flythroughs or orbits. The z-depth changes aren’t so much caused by proximity of the particles to each other, but from the camera angle changes causing sprites to be either in front or behind each other. When I can get away with it, I will often use additive transfer modes, and that can work depending upon the situation, but not always.

I’m not sure I’ve ever seen a 3D engine that can crossfade between passing sprites. It could probably be done, but not sure how. I’ve not seen anything in C4D like this either.

Television Producer
KTVF-11 Fairbanks, Alaska
video.ericbarker.com


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Kalleheikki Kannisto
Re: Particle Sprite Z-depth pop
on Jan 16, 2019 at 2:54:20 pm

Can you share an example (video) of a scene with this problem with the type of camera move you are doing? Seeing what you are dealing with might prompt other ideas.

Kalleheikki Kannisto
Senior Graphic Designer


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Richard Garabedain
Re: Particle Sprite Z-depth pop
on Jan 16, 2019 at 3:33:48 pm

I wish particle world did not have this problem...it is it's single most limiting factor


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Eric Barker
Re: Particle Sprite Z-depth pop
on Jan 16, 2019 at 9:28:33 pm

Here's one of my videos where that was noticeable. Look at the clouds, it's most noticeable around the 55sec mark when looking straight down:







At first I thought there was some particle pop-in, but ran some tests and found it's caused by sprite overlap. My boss and I finally decided to let it slide in this case, but I've been hoping to find a way to fix it. We do a lot of these, 2-3 a week of different designs, so I run into this quite frequently, and I'm tired of having to adjust my content to try and avoid it.

Television Producer
KTVF-11 Fairbanks, Alaska
video.ericbarker.com


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Blaise Douros
Re: Particle Sprite Z-depth pop
on Jan 16, 2019 at 5:36:48 pm

Could you solve this by using separately-layered instances of your particle generator, each with a different Z depth? Three layers, Close, Mid, and Far. Cut the total number of particles down by 1/3rd, and let the multiple layers create the overlap effect.


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Eric Barker
Re: Particle Sprite Z-depth pop
on Jan 16, 2019 at 11:42:43 pm

With a static Camera it might be possible depending on the circumstance, but it usually isn't an issue with static cameras anyway, I tend to just have all the particles moving the same speed relative to each other. The problem is I do a lot of camera orbits and fly throughs, as in the video above. I'm often using multiple layers in conjunction with Element3D and Cinema4D elements.

I'd eventually like to get into doing true 3D ray-marching clouds (not even sure that's possible with C4D), but for now, cloud sprite particles tend to be the best bet. I custom make a cloud loop using an initial Particular system with shading, render that, and use it as a sprite. Cloud 3D geometry hasn't really hit AE/C4D in a processor-friendly way yet. Curious because Unity can do it real-time with GPU rendering (Horizon Zero Dawn is probably the most advanced example). In any case, until C4D or E3D introduces ray-marching cloudlet geometry, sprites are still my best option.

Audio/Video Production
Relaxing White Noise, LLC.


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Blaise Douros
Re: Particle Sprite Z-depth pop
on Jan 17, 2019 at 8:38:29 pm

Is there a reason CC Particle World won't work for your application? I did a really quick test with it: using a textured faded sphere as the particle type, and a cloudy turbulent noise pre-comp as the texture. If you duplicate two to three instances of it, each with a different random seed, you limit the number of overlaps between sprites on a given instance, and can pretty much eliminate pop-in that way, while still creating the illusion of a crowded cloud field. This works even with a fairly complex camera move--as long as you're not flying too much directly into the producer, I saw very little pop-in.


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Eric Barker
Re: Particle Sprite Z-depth pop
on Jan 18, 2019 at 2:48:11 am

That can be done just as well with Particular. I don't really see the purpose behind using multiple instances. With complex camera moves, that can get very weird very fast (distant particles passing in front of closer particles on a different layer). I can imagine that might be a workaround for projects with a static camera, but not with ones involving 360 degree camera moves like I'm usually doing.

I think you misunderstand, I WANT particles to be able to be able to pass in front of and behind, and even through each other, I just want to avoid a sudden "pop" when they do. I envision a particle generator where you can give sprites a Z-depth mass, and have them cross-dissolve between each other when they overlap. I don't think anything like that specifically exists, but was curious whether someone had come up with some kind of workaround.

Audio/Video Production
Relaxing White Noise, LLC.


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Blaise Douros
Re: Particle Sprite Z-depth pop
on Jan 18, 2019 at 7:08:43 pm

Yes, I understand, but given that this isn't possible with any of the current particle generators, a multi-layer approach may be your best (and only) option. Especially if you're building cloud particles that have partial transparency, I think it'll look a lot more seamless than other approaches. If you're worried about layer order, the solution is...more layers that you can bring in or out to compensate for the perspective changes! Heck, you could use three particle generator instances, and create precomps with collapsed transformations where the layer order is reversed, and that way limit the number of crossfades between layers.

It's always nice to think of a one-stop, fully automated solution that would solve a problem. Unfortunately, as you know, a lot of creating VFX is making stupid workarounds, custom scripts, and special setups to get around program limitations that are particular (har!) to our situations. I think that's probably the position you're in at this stage!


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Eric Barker
Re: Particle Sprite Z-depth pop
on Jan 19, 2019 at 1:49:54 am

Definitely agree with your last point there. Still don't think multi-layer instances is an option for my particular cases, considering I often swing around the systems, particles need to be able to overlap each other naturally in 3D space. But you're correct, motion graphics and VFX are ALL about "HACKS".

I thought that there would be less when I started working in a "true" 3D environment (Cinema4D), but on the contrary, there's even MORE! In some ways, 3D graphics is all built on a completely made-up interpretation of how light works (e.g.: in the real world there is no difference between specularity, reflection, and diffusion). "Shaders" are ALL made-up concepts that emulate, but don't simulate, real-world scenarios. Bump mapping is an amazing, silly, and ingenious example, too.

However, in this case, sprites are such a commonly used stand-in for volumetric geometry, that I'm sort of surprised someone hasn't designed an engine to give them fake volume for cross-fade compositing, that strikes me as an incredibly useful technique. Maybe this is found on game engines like Unity, where sprites are used practically everywhere.

Audio/Video Production
Relaxing White Noise, LLC.


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