Tips for Abstract Effects in Houdini
Building abstract effects can be either really easy, or super hard depending on which type of artist you are. For me, I love abstract work, but sometimes struggle when it comes to physics based, or reality based work. Unless it's clouds. :)
For a lot of artists it's the opposite. If you ever went to a VFX school then they probably taught you how to focus on destruction work, particles, or pyro effects. They most likely leaned away from abstract work, as it's more harder to teach and requires more complex concepts. So let's talk about some easy abstract effects we can create, and then some more difficult ones. I might make a part two to this article, so stick around. :)
Some Friendly Co-Worker Advice
Before writing this article I sat down and talked to one of my close friends, and a fellow Houdini artist. His name is Andrew. He's been working in the industry for a solid three years now. He's worked on a few different blockbuster movies such as Wonder Woman, John Wick 3, and X-Men: Dark Phoenix. He's probably one of the best complex simulation artists I know. Here is a few things I've picked up from him over the past year. I'll be sharing some of this knowledge, and I'll be doing this through out the article, not just in this section.
Focus. Don't be overwhelmed by what you know, or what you think you have to do. But find the easiest way for the solution. When applying this statement to abstract effects, it's important not to be overwhelmed by ideas. Too many ideas can lead to too many ideas to create the effect.
Vellum is a bit more complicated than you think. So don't get frustrated if something goes wrong. Keep trying if something goes wrong, and see if a a vellum DOP works better than a vellum SOP solver.
Don't be afraid to split a simulation into two or more parts. Or two different simulations. Sometimes attributes overlap or change values rapidly. The only easy way to do this is to split the simulation into pieces.
Most abstract effects are created out of lines, particles, and models. So those will always be good starting points for your effects.
Don't be afraid to get a little VEX heavy.
Abstract Modeling and Materials
The easiest way to make an abstract model look cool is changing the subdivision and mesh shape and then polywiring it. This is a fun and simple way of creating something weird, and at the same time seeing how you can manipulate your polygons to different shapes.
Selecting and grouping either the points, vertices, polygons, or edges of your model also helps. By grouping only certain areas of your object, you can tell different modeling nodes, such as the bend SOP to only affect those areas. This can help give variation to your model.
The Mountain SOP is always a great idea to add abstract movement to your model. By adding an expression such as $FF/34 in one of the offset values, you can get the noise to move across your model. You can also use it to give your model variation to their shape before you add it to a sim or another piece of geometry. The Ripple SOP is also good for this purpose as well. However, it adds an animated ripple across your object. It's great for adding or faking a water effect. But it is heavily position based, so the ripple will change based on the position of your object.
Playing with your Cd attribute is also a quick way to randomize the color of your object. The Color SOP has multiple functions to randomize your color based on attributes, position , or range of values. This Cd value can then be promoted to impact the shade of whichever material you decide to add to your creation. You can also play around with any other attribute your object my possess, and change it to impact your final product in any way.
The Boolean tools in Houdini are also really great for editing your model. They allow for you to take two objects and chose whether you would like to intersect, subtract, or change the shape of one model based on the other. You can also have one input on the Boolean tools be a model, and the other be a simulation. Then over time, have the model be eaten away by the simulation.
Shaders and materials can be a bit more tricky to use. Building Houdini shaders from scratch is often so complex, it is left to senior artists at studios. However, this Masterclass Tutorial Here by Kai Stavginski is a great way to start that learning process. By randomizing how you apply your shaders to different parts of your object, you can create variance on the shader interprets your model. This is a good idea if your model breaks apart, you need the inside shaded differently, or the material need to change over time on the object. You can also lay down a Material SOP chose which parts have which shaders applied to them.
Abstract Particle Systems
Particles are a quick and easy way of creating something weird and fantastical. There is almost an unlimited way to generate particles from any object inside of Houdini. As well as animating, pulling or pushing, or moving them in any form. As soon as you connect a POP Network to anything, you'll be able to create dynamic particles from your geometry. Otherwise, you can just use a scatter to create static points on an object.
One of the best way to create twisty abstract shapes with particles is to use the POP Axis, or POP Curve Force nodes inside your DOP network. The POP Axis Curve force will allow you to orbit, follow, or life your particles in or around a circle. The POP Curve Force takes a selected curve that is inputted into one of the DOP network's inputs, and does the same thing. However, it allows more customization.
You can also use POP wrangles, regular POP forces, or inherit the velocity from your emitter to add more variation in your creations.
Abstract Pyro Effects
Abstract Pyro effects build of the concepts discussed in the modeling and particle sections. If you are creating a smoke effect for a mystical character, a smoky creature, or whatever else you can think to create with pyro, it will most likely be classed under abstract. The more abstract your emitter is, the more creative your effect will be. For most pyro effects your emitter can be either particles or geometry. Keeping this in mind, lets get started.
I wrote a previous article about explosions (which you can find HERE), which covers some basics of using pyro. I won't be going over basics here, but feel free to read up on them.
Houdini 18 now has an option to create colored smoke. This is a great way to generate color values in your smoke quickly, and at the same time generate abstract colors. Or can change the color of your smoke on your billowy smoke shader by adjusting the emission and temperature color.
By adjusting the disturbance value on your pyro solver, you can have the option of adding harsher turbulence in the simulation, or reducing it to add detailed smoke curves. You can also reduce random forces affecting your sim by reducing the block size.
By manipulating the velocity of your emitter or simulation you can create even more interesting effects. By changing or animating your velocity over time, you can change the speed, movement, or expansion of your smoke as it moves. When you randomize any velocity on a simulation, you can also create very jagged or explosive movement. So be careful unless that is the look you are going for.
Playing around with the gas DOP tools are also a great way to manipulate your simulation. Inside your DOP network you should have access to nodes such as Gas Turbulence and Gas Dissipate. These are great for editing the flow of your smoke or other pyro creations.
You can also add Volume Slice and Volume Trail SOPs before your pyro's DOP network to vary the velocity and movement even more. The Volume Slice SOP will slice through any chosen volume, and you'll have the ability to cut through it and see the velocity that is spread throughout the volume. You can then use these velocity trails to move the smoke simulation in a desired direction. For the Volume Trail SOP, you can also use it for the same thing. However, this node relies on the shape of the selected volume, and points that it can add velocity trails to. You'll need to also use a scatter node with this SOP as well.
Overall, play with the noise and curl of your simulation for the best results. The more cohesive the movement of the simulation, the more it will make sense.
The smaller your smoke emitter the bigger your block size. Vice Versa for large simulations. This will help add more detail in your simulation.
When presenting abstract effects. You need to keep in mind how you would like to show your creation, and still make it coherent. You can't always do big camera movements through the scene, or have a static camera. You need to experiment and think about what works best for the scene.
Because most abstract effects rely on modeling and particles, you'll need to create a great focus on the model or moving parts of the creation. For a still model, you'll probably need to focus on the lighting to set the mood of the effect. As well as doing an overall pan around the object. If the model has moving textures, then try and create a good focus on that.
If you simulation has moving parts, bring move focus to the interactions your creation is making than it's overall look. This will help your simulation look more dramatic, and as if it has a desired purpose.
Abstract FX in Houdini: https://www.cgmasteracademy.com/courses/14-abstract-fx-in-houdini
Abstract Visuals - Houdini and Redshift: https://www.sidefx.com/tutorials/abstract-visuals-houdini-and-redshift/
Abstract Stuff in Houdini - Discord: https://forums.odforce.net/topic/42078-abstract-stuff-in-houdini-discord/
Houdini for abstract 3d motion graphics - is it possible?: https://www.reddit.com/r/Houdini/comments/9pafmj/houdini_for_abstract_3d_motion_graphics_is_it/
Houdini Quick Tip - growth abstract shape: https://www.pinterest.es/pin/304767099782144057/?lp=true
Houdini Tutorial 03 . Volume Abstracts: https://cgbeer.com/houdini-tutorial-03-volume-abstracts/
Houdini – Abstract Polygon Growth Effect Tutorial: https://cgterminal.com/2017/03/15/houdini-abstract-polygon-growth-effect-tutorial/
Detailed Smoke, CGWiki: http://www.tokeru.com/cgwiki/index.php?title=SmokeDetailed
Smoke and Pyro, CGWiki: http://www.tokeru.com/cgwiki/index.php?title=Smoke_and_Pyro
Houdini Questions, CGWiki: http://www.tokeru.com/cgwiki/index.php?title=HoudiniFAQ#Todo
Differential Curve Growth: https://forums.odforce.net/topic/25534-differential-curve-growth/
Curve Unroll Tutorial, CGWiki: http://www.tokeru.com/cgwiki/index.php?title=CurveUnrollTutorial
Houdini VEX, CGWiki: http://www.tokeru.com/cgwiki/index.php?title=HoudiniVex