Using Houdini To Simulate Paint Smearing

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We’ve been asked by Patrick (www.altshift.de/) how to pull off something like these beautiful paint smears (vimeo.com/2727...) in Houdini, so we got to work. Using basic FLIP techniques will get us quite far, we just have to find the right settings. (Haha. “just” finding the settings…)
In this tutorial Mo covers setting up a basic viscous FLIP sim using animated colliders to create the impression of acrylic or oil paint being smeared around with a brush.
Download Project File: www.entagma.co...

[@primal1585]

this man has a very calming teaching voice, time to boot up houdini now

[@HarryNicNicholas]

you are now under his complete control.

[@devfromthefuture506]

I don't know nothing about computer graphics I just opened this video to sleep better listening to his voice

[@zurasaur]

One of the greatest flip tutorials of all time, simple setup, beautiful result - amazing for beginners. Thank you entagma

[@carlosrivadulla8903]

I absolutely love how u give a brief explanation every time u drop a node or change a parameter

[@DirkKool]

imagine somoene painting a complete painting with this, including the paint drying and stuf! amazing work !!

[@joelface]

I can imagine, one day, painting in VR, where you're picking up paint with a brush and smearing it around in real-time simulations that look like this. :O

[@eftorq]

You make it look so easy and obvious! Wouldn’t have thought of the approach to spawn some paint beforehand and then distribute it on the surface. Thanks for the tutorial!

[@BobSk8s]

I did essentially this a few years ago experimenting, but mine was very cumbersome and messy which was ok as I was just goofin'. Very pleased to see I was on the right track.

[@koltscats]

This is exactly something I was wondering how to do! and you made it so simple! ahhh, humbling.

[@DolioFoilio]

Didn't understand a thing from this video (Simple Blender guy here) but it was extremely enjoyable to see the process & node based environment. Houdini is a real beast but super powerful. Good job, love the end result. (Did I also mention you have a great narrator voice?) :)

[@s7tmbr]

Hi, if you have any question about anything shown here, let me know. I would like to help with Houdini and spread my knowledge with everybody (even if it isn't that much yet lol).

[@DolioFoilio]

@@s7tmbr Thanks a lot dude, Appreciate it a ton! :)

[@andrewsausman]

@@s7tmbr Hey, i downloaded houdini yesterday and really wanna try this out ... is this kinda video beginner easy or are there other ones you'd recommend ??

[@s7tmbr]

@@andrewsausman This video from Entagma is pretty fair forward and easy to follow. I would start with "Houdini isn't scary" series on youtube for complete beginners.

[@ENiGMA_Atelier]

@@andrewsausman definitely not start from this. houdini is very board there are so things you can explore you might get lost. I think its good to have some fundamental knowledge one procedural modelling, how it handles data and attributes**, and then maybe go into vex and vops. I started by trying to construct a single line in houdini through vex... and also, you can look at indiepixel video as well. he has a nice voice too haha

[@vipergx]

Thank you for this. Was just working with fluid sims and meshing them. This helps. Just like every Entagma tutorial ;)

[@banno1992]

So much amazing knowledge/ info condensed into 15mins. Thank you. Tried to do this a year ago and mine was so clumpy in contrast to this

[@jamesconkle9158]

Wow what a perfect Holliday present! Thank you 😊

[@yuzhenwang9764]

For anyone on macOS getting an error when you run it for the first time, disable the OpenCL option and it should work as expected.

[@jorgeyepezlazo8773]

Is this possible with the new MPM solver?

[@hotkar]

gave out a try and total satisfying 🤩🤩

[@AlexisRivera3D]

Can you export his to Blender?

[@curiouspers]

Happy new year! ❤️

[@loganpenciu7317]

Thank you, this is great! Always appreciated!

[@TheDanielConsole]

Entagma posting a Flip tutorial? Yep, it's Christmas alright 😁

[@primitifsound]

I am now sure our world was created in Houdini :D

[@bush9686]

thanks a lot! Could you advise any tips in order to simulate Lava Lamp like fluid? thanks in advance.

[@UnbekanntesSubjekt]

LOVE THIS. Period.

[@devvishwas1232]

Thanks

[@igobyzak]

Beautiful! Thanks so much!

[@DataJuggler]

5:18 My ground plane doesn't show when I connect it to merge2 like yours does.

[@chr1st0pher]

wowww so many clever tricks. im curious about how the trail sop to compute velocity works on the sdfs though? i wouldn't have expected that to work i assumed it only did on geo with consistent topology.

[@alaabelguith-2768]

thank you

[@newrule3139]

Im having an issue with the oversampling, when I increase it, even to past 100 it doesnt add much time to the simulation? I am also getting quite a blobby and flickering look when I cache out the final fluid surface? I can figure out what I am missing? I havent changed any other parameters. Any ideas here?

[@juancarlosgzrz]

How can it be done for toothpaste coming out of the tube?

[@metaturnal]

Awesome as always. Just out of curiosity: Do you know if the scale has an impact on the result or not? Like for the flip sim, does it make a difference for the FLIP sim at what scale I would do this? Or is the result the same if I scale everything accordingly = multiply the overall scale and the relevant parameters like particle separation by say 0.01 (scaling the whole sim from a size of 32m to 32cm ; ) If my goal was to have an accurate sim is it good practice to work in real life scale from the start? I guess for rendering at least it is good practice to work with real world units. Since the meshing occurs after the sim, I can simply use a transform, without having to re-sim everything, I assume.

[@divonoartista9904]

As a painter and Blender user I love this brushstrock of color, Houdini looks very powerful, I wonder can it also be done in Blender? thank you

[@AlenHR]

I believe so. Blender has Flip Fluids Addon, supports VDBs, and even has a node network. I'm not sure about the level of refinement and control you would have, tho.

[@黎晓荣]

Hello, I am a 3D hobby student, this video of yours is amazing, can I ask you how you do it, thank you

[@DIGITALMEAT]

Nice!

[@ainjeffery]

How would we go about making a letter using this paint? for example "O" ?

[@FaddyVFX]

Maybe in flip solver geometry seperation turned on and lowered will result in more detailed brush stroke because flipSolver generates its own collision vdb internally, thank you for this beautiful tutorial.

[@herculesmare4209]

great tutorial.

[@bn3d128]

Thank for tutorial

[@mohamadhosein7917]

sorry i have a question since i am not a professional in houdini, in 2:45 u place a mountain node but it comes as an attribute noise for u but a regular mountain for me, how should i fix that?

[@Entagma]

Sounds like you're not using H19 - Mountain has been replaced with a particular preset in the attribute noise in version 19. Cheers, Mo

[@mohamadhosein7917]

@@Entagma yesss, you are right thanks

[@gfxfarhan]

Hi sir I am following your donut in houdini video and I use houdini 19 but sir in houdini 19 the visualizer is very different. How can I get your results in houdini 19 please sir must reply.

[@Entagma]

Hi GFX Farhan, for a bit on how H19's visualizers work have a look here and also pay attention to the first comment below this video: kzbin.info/www/bejne/iYi0faerqc2aorc Cheers, Mo

[@jasonsong2956]

super cool!

[@lucasthorley]

Is there any way to get this simulation to continue indefinitely, for example along a curve with 'infinite paint'?

[@MrJmal95]

Fluid comes out very splashy... i cant find a way to control it after some tests!

[@nilestanycosta863]

yesss!

[@sanderschat]

sorry to sound a bit silly: but Houdini is like Blender?

[@austin_wendenburg]

Thanks for the knowledge Moritz! Is there any reason you choose to go with FLIP over the new vellum fluids? I was under the impression vellum fluids would be more suited for smaller scale sims such as this

[@Entagma]

Hi Austin, in my preliminary tests when preparing this setup, FLIP turned out to be faster than vellum Fluids, but that might be to blame on my weird test setups. Cheers, Mo

[@austin_wendenburg]

@@Entagma if it works it works! lol cheers, thanks again!

[@lewisvtaylor]

@@austin_wendenburg the vellum fluids being sort of SPH means you need ridiculous substeps as viscosity rises, to stop the particles exploding. FLIP doesn’t require the substeps to maintain stability.

[@austin_wendenburg]

@@lewisvtaylor That's good to know! Cheers, thanks for sharing.

[@STUDIO-ORBIT]

How would you go about making the paint thinner and more water like?

[@Rick_Sanchez_1337]

Lower the viscosity

[@arjunladdhad8792]

How do i take the vdb file so that i can import it in blender? If someone knows this place tell me

[@saifsami_ss]

Thank you so much

[@charlzdalton5261]

Hey Mo, why u didn't simulate it with vellum fluids? Small scale, high viscosity - seems pretty good for vellum, doesn't it?

[@Entagma]

Heyhey, When I prepared the setup, FLIP was faster, so I stuck with it. :) Cheers, Mo

[@rhinasons]

in the dopnet. I tried to unlink the volumeSource to the flipsolver and change the flipobject1 sop path to outSource ,it still work. So ,anyone knows why use both flip flipobject and volumesourse.

[@jostermayer]

can you do a karma render tutorial on this :)

[@no-one3795]

I wonder. Can you make a painting inside Houdini? A mona Lisa perhaps?

[@PawelGrzelak]

Pretty awesome. Did you also try vellum or this?

[@Entagma]

Yes, I was when deciding which route to go. In this case FLIP turned out to be a bit faster than vellum. But that might have just been my weird vellum settings. Cheers

[@PawelGrzelak]

​@@Entagma Thanks for answer. I wouldn't expect vellum to be faster, just were curious if you tried. This first iteration is pretty slow TBH but I don't have much experience with fluids. I've seen the original animation Malaki - Molasses long time ago and always wanted to try to recreate. Thanks or the tut Mo.

[@kreatoarchidesigns3096]

Hi , this is wonderful ..can u pls teach the same in blender

[@ArtOfMkUltra]

if entagma can figure it out, than NO can you.

[@extremosdeloscasosquese3970]

Thanks!!!

[@MihajloCiric]

Is there a way to export this to unreal engine 4 ? maybe bake the animation to a mesh or convert it to be used witch niagara

[@Entagma]

Yes. For example the VAT export from SideFX Labs. Cheers, Mo

[@blartimore]

Hi Moritz, a question if i may, how to mix UVs, for example if i were to "mix" 2 or more paint emitter/particles? Or if i'm using an image as my material? Thank you!

[@Entagma]

Heyhey, you can add any attributes you like to your points after the flip source in SOPs. Be it uv coordinates, color or whatever. E.g. try using an attribnoise set to generate a float followed by a color node set to ramp by attribute and see what that does to your fluid's colors. :) Cheers, Mo

[@iamsoutherland]

@@Entagma This tut is awesome! Would love to be able to set the color of the particles t the beginning that way the brush smears the colors. The Noise just colors the paint and does not set and smear. Any tips?

[@metaturnal]

​@@iamsoutherland Second that. Also I managed to color the particles, but would like to retain the color after the meshing, for the render.

[@metaturnal]

Oh, so I just fiddled around a bit. Disclaimer, I have no I idea if this is proper, but it seems to work. I created two flip sources, gave them different colors. Simply merged them before the OUT_Source. Then in the Particle Fluid Surface In the transfer attribute field I typed: Cd Now The mesh has two colors, that are mixing. Maybe add an attribute blur to add the nasty borders as the colors are applied to polygons? Better solutions welcome.

[@jochenbijnens7019]

@@metaturnal Thanks man, great solution! Quick question though... Do you by any chance know how I can apply separate materials to both flip sources? When rendering with Redshift, for example, I can add a RS User Data Color node in my material, which allows me to use both colors I've used before merging the flip sources. That's already great... But what if I wanted to apply two completely different materials to both flip sources? Cheerz!

[@bogscave]

Hey, I'm also new to houdini and have a lil question, is it possible just to duplicate those systems and make them interact with each other (combine 2 colors for example)?

[@Entagma]

Heyhey, I'd rather use two separate FLIP Sources emitting differently colored particles in the same Simulation than trying to get two separate FLIP sims to interact. Cheers, Mo

[@bogscave]

@@Entagma oh, ok, will have to get there haha also, is there any possibility to export the simulation to C4D (for Redshift Rendering) and having colors interacting? And thanks a lot for helping out!!

[@abiyyupanggalih854]

I'm not a Houdini user, but I want to ask some question -is Houdini usually works through Node?, and not touch that 3D viewport (except for navigation maybe) - and is this software can also use for basic modeling?

[@starzilla2975]

Although you can do translations and editing stuff in the viewport... Houdini is at it's best when used to do procedural tasks with the nodes, that is where all the power behind it is and how it's normally used. It definitely can do modeling too, but definitely for procedural things that would be very tedious for a normal artist like making an entire city or an asteroid field. But I much prefer to model a lot of things in Maya or Blender and then importing it in to Houdini unless there is a good way to do it ising the nodes.

[@abiyyupanggalih854]

@@starzilla2975 wow thanks for the explanation

[@nataschafarmer1980]

Does anyone know how to export this animation to UE4? Not a clue how to use houdini and dont know how this would work

[@Entagma]

I have the feeling you could use SideFX Labs' VAT (Vertex Animation Textures) tools to pull this off. Cheers, Mo

[@jeremy3ddave422]

Pls.. we need a blender version of this in Blender Geometry Nodes

[@mstfrzrm]

f... now i have to do this

[@nobody-u-know]

this is a great tutorial, but details like adding a trail node are frustrating. How would we know that we need velocity data? How would we know that the trail node provides this? I would easily be stuck, and have no clue that I needed this. Actually, it seems to work fine without it. Why did we need this? Does this provide vertex velocity data on the particle fluid surface?

[@manuelst3004]

Hi. I'd like to become a patreon but I'm having issues. I emailed you a few days ago. Maybe it got lost in spam folder? Thank you!

[@Entagma]

Weird, can't seem to find your message. Would you mind resending it to mail(at) entagma.com ? Thanks, Mo

[@manuelst3004]

@@Entagma hi Mo. Just did. Thank you

[@manuelst3004]

Did you ever recieve it? Anyway, I think I managed to solve it

[@ghost3dee]

the sim may look okay, but scene and objects scale are completely off. The emitter is 5 meters high, the whole brushstroke sim is 30 meters long . Did you change the scene units in Houdini settings before or am i missing something? Thanks

[@Entagma]

Heyhey, as per my understanding Houdini is unitless, so you can "correct" the size by just scaling down your sim globally if it's irritating to you. :) Cheers, Mo

[@ghost3dee]

​@@Entagma Houdini solvers and integrated forces are closely linked to scene units (1 meter/unit by default). A flip sim of wine poured into a 30 meter glass would behave like an ocean. A brushstroke simmed in a 30 meter domain and one in a 30 cm domain would look and behave completely differently (provided that forces like gravity are not adjusted/multiplied to the same magnitude). I tend to respect the scene units by adjusting the scale of incoming geo to match real life sizes of objects. It just threw me off a little to see an emitter of such size. Thanks for the reply!

[@polkablues]

@@ghost3dee You're totally right, but I don't think it matters so much in this specific case just because the viscosity is so high, the only real interaction being simulated is between the source and the collider. All the gravity force is doing is holding it to the ground plane; you could pretty much set it at any negative value and the results would be the same.

[@AllegedlySpiffy]

Hmm yes, yes, I know some of these words.

[@briewi]

Would love to see this done in blender, there’s no tutorials on this and it’s exactly what I’ve been wanting to do

[@dieuwerf]

Don't rely just on Blender to be able to do everything, it cant. Especially for these types of effects programs like Houdini will just be way way more powerful. That aside, learning houdini will also make you a better blender artist, you'll really be forced to understand core concepts that are also used in Blender and all other 3D Software.

[@tomallen5837]

Indian Paintbrush eaque

[@shoessure5127]

i came

[@lawrencedoliveiro9104]

Why not try Blender’s Dynamic Paint feature. Might be easier.

[@extrathicc78]

Can you interpolate the collider on a spline? For the sake of something like lettering using this simulation

[@Entagma]

Sure, you can animate the collider to your liking, either via keyframes or to follow a spline. Cheers, Mo

[@CHITUS]

this man has a very calming teaching voice, time to boot up houdini now