Power Up Your Houdini Skills with SideFX

Power up your Houdini skills

SideFX Houdini

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Making The Last Bastion

Blizzard Animation Country USA STAFF 200 (across all departments) software Houdini, Maya, Mantra, Redshift, RenderMan WEB blizzard.com

Making The Last Bastion Ian Dean discovers how Blizzard Animation harnessed Houdini to create the dense foliage for its latest animated short

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Many techniques were used to create the moss

hile the Overwatch game was released to acclaim earlier this year, Blizzard Animation has been steadily releasing short animated films to expand the back-stories of the leading characters. Of the five episodes, The Last Bastion stands out as an incredible technical achievement, and uses Houdini to create a large, dense forest environment and foliage.

The short presented some artistic challenges for the animators. Project director Ben Dai explains that one goal was “to tell the story of Bastion without any dialogue. Another major goal, like all the Overwatch animated shorts, was to expand the game universe by telling great stories about our heroes.”

For VFX supervisor Jeff Chamberlain, it also meant doing things a little differently. “I was hoping we could tell a story that wasn’t

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typically what you’d expect from Blizzard Animation, but still universally appealing enough to be accepted by our audience.”

Doing things differently meant pushing the FX as much as possible. Houdini has been the Blizzard FX department’s package of choice for the last few years, and FX supervisor David Stephens explains that many of Blizzard’s artists come from a film VFX background, so making more of Houdini seemed a good direction to go in.

“When we were going into this there was a question of whether the plant work would have to be done in Maya, in traditional rigging, or in FX, so getting some of the early results with the hair solver seemed to confirm that we were able to do it,” explains David. “Certainly when we were testing some of the heavier trees, when you get up to hundreds of thousands of branches and

millions of leaves, the fact that we could process that and get it to rig correctly was a good moment for us.”

Moving moss The animated short includes plenty of standout moments, but it’s the undergrowth, forest foliage and shot of a flowing grassy field that are technically impressive.

“We were pretty fond of the shots where Bastion stands up and emerges from the undergrowth. These were a combination of plant wire simulations riding on top of PBD simulations. They were fun to see come together since so many people and techniques were involved,” says David.

To achieve the detailed feel, the team had to custom model the plants, leaves and trees,

using the 3ds Max plug-in GrowFX, which the modellers then further modified and sculpted in Maya and ZBrush, allowing a fine degree of stylisation. The moss on Bastion was sculpted in Maya and then covered in fibres using XGen.

three layer thing: we had to take the shell of the moss and that was converted over into a PBD sim in order for that to all kick off as a mass when he’s standing up,” explains David, adding: “As to do the soil sim we had to reattach all of the XGen moss hairs that had

when you get up to hundreds of thousands of branches and millions of leaves… that was a good moment for us

David Stephens, FX supervisor, Blizzard Animation

“They [the art team] had to custom model a lot of the plants and growth that was around and on top of Bastion, and there was also a layer of some standard library plants as well. So effectively, we had to do a two or

Animating in FX as well as traditional rigging worked wonders for Blizzard

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been generated over on the Maya side and reoutput those so that the moss would actually track with it, all in Houdini.”

For the plants, the team would end up merging the two or three different layouts

industry

Making The Last Bastion

Plant rigging in Houdini FX supervisor David Stephens explains Blizzard’s approach to creating plant animation

Foliage on Bastion was created from up to three layouts of auto-rigged plants, leaves and flowers

that they had made to create the different plants that lived on top of Bastion. These had been through the process of auto-rigging and had been broken down into their components – details, leaves, flowers and buds.

“Eventually, you’d have this great big wire solve that is using the previously done soil simulation as a route anchor for those curves, and then all of that is simulated. Then all of the plants’ hero geometry is deformed based on those curves, and on additional procedural animation based on pivots for the leaves and buds, and [it all] stacks up two or three layers deep for the final result.”

“It’s one of the scariest networks of all time!” exclaims David. “It’s a large system that took months to build. The network is hundreds and hundreds of nodes, and networks within networks.”

“We developed a unified approach to the plant animation using Houdini. The first stage of the process would take a completed plant model and derive the branching structure through an iterative search algorithm. This worked surprisingly well – even for trees or bushes with tens of thousands, or even hundreds of thousands of branches.

Next, the process [team] would figure out the attachment point of leaves, flowers, buds, etc. relative to the branch structure,” says David.

This meant the team could then build a hybrid ‘rig’ for the plant, explains David: “Portions of the hierarchy would be simulated using the Houdini wire solver and all other portions animated procedurally. We developed a rich suite of tools to define the simulation and procedural animation behaviors.”

It meant the team could then create a large library of plant animation cycles

for each plant at varying wind intensities. “These plant cycles could then be dropped in by the Layout department to create general ambient motion for the forest and plant cover,” says David, explaining: “For more complex shots requiring character interaction or specific choreography, the plant rigs could be loaded into a live scene with collision objects and simulated in Houdini’s DoPs module.

The plants on Bastion himself were simulated in this way for most shots.”

Ground work The development on the soil sims took three weeks. The plant system itself is something Blizzard developed over a period of months, and for The Last Bastion this is more an application of that wider system than something developed for the short.

“Essentially, we had a combination of both library plants and then we had custom plants – that was kind of interesting as we just received this giant lump of greenery and we had to kind of go through that and break a few things out so we could convert them into rigs, that’s probably two or three more weeks of custom work setting up the plants,” reveals David.

Another standout moment comes towards the end of the animated short as Bastion

An auto-rigging system in Houdini was used to setup plants for both simulation and procedural animation

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industry

Making The Last Bastion

emerges from the forest and walks through a field, a sea of flowing grass. This was done using a Mantra volumetric shader created by senior artist Matt Cordner, to create the distant fields of moving grass, complete with independently moving grass blades.

“The grass is actually in three layers,” says David, with the closest part to the camera being the ‘hero portion’, where the character would walk through and interact with the grass. “Basically, every stalk in there is a wire going through a massive wire solve. So that ultimately ended up being the hero section of the film, and then a second section beyond that uses a Houdini hair system to set up a bunch of curves – some we use as hair renders that actually go back into Maya, but we also use it to drive some rigidly bound instances of some of the plants.”

David continues: “In the hero section, closer to the camera, each of the plants has a wire and fully deforms and bends. The next section out – maybe 50ft beyond that – ends up being a combination of hair and these instances that are being rotated based on a hair and follow the hair. Then, in a third

This layer and the one above show the geometry for the grass that appears closer to the camera

Matt Cordner wrote a Mantra volumetric shader to create an instant field of moving grass

the system we created for the last bastion is one of the scariest networks of all time!

David Stephens, FX supervisor, Blizzard Animation

zone beyond that, is a volume shader that was written for Mantra, which produces this lovely cheat from the distance that produces these moving stalks… a volumetric cheat, it’s pretty cool.”

The three layers come together in the final shot to create a grassy field with realistic depth

Shortcuts In terms of ‘cheats’, Blizzard overcame the workload of a project like this by considering the shorts as a whole, and also thinking about how they fit into the video game production. The flashback battle scene in which Bastion remembers his war-torn past was one area that especially benefitted from this process.

“At the outset of producing these shorts, we consciously began building up a repertoire of FX techniques that would fit within the game’s art style, so with that battle scene, you’re seeing the amalgamation of many of those FX all in one place. Each effect is reasonably stylised, but the scene complexity pushes the overall look back towards something that reads as real,” explains David.

Blizzard’s cinematics team developed a large number of gun-related effects that created with Houdini and Mantra, which

came in useful for the battle scene. Over a period of weeks sever artists pieced it together. A HDA - Houdini Digital Asset (also known as OTL) written for The Last Bastion can be used in future cinematics.

“We tend to write a lot of tools for reuse or as starting points for later development, so there’s quite the suite of OTLs [HDAs] now for gun fire effects, lightning, and lately, plants,” explains David. “Because a lot of what we do is custom to the shots, in a lot of cases we have to leave things a little bit looser so that we have room to tear it apart and rebuild it for the next show. When I say we have one OTL [HDA] for a gun effect, we probably have five or six OTLs [HDAs] – from the flash to the sparks to the shells to the tracer fire, it’s a whole suite of tools.”

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David has been using Houdini for 20 years, so a project of this complexity didn’t phase him, but he does identify what has changed to help newcomers.

“Some of the Shelf buttons and interface advancements that have happened in the last few years help a lot. I think the Wrangle nodes help tremendously because you can get some decent sized programs going there without having to write HDK or do a compiled operator the way you did years ago, and so those things have really helped out and made it more accessible… It’s really very powerful, we wouldn’t change Houdini for anything but calling it easy and accessible does it a disservice.”

Watch The Last Bastion short animation FYI at www.bit.ly/tdw-bastion

FEATURE

Get to grips with Houdini

become a Houdini wizard Mark Spevick, head of 3D and course leader at Escape Studios, explains the key things you need to know to flatten the Houdini learning curve

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oudini has traditionally been viewed as having a steep learning curve, particularly when migrating from other 3D software. Houdini requires not only good basic knowledge of 3D animation, but also a whole new and different way of thinking compared to traditional 3D software.

Understanding these differences, and getting your head around a few other concepts, is key to demystifying how to work within Houdini, and will help to reduce that steep learning curve.

After many years of using, learning and teaching Houdini to people of all levels, I want to share with you some key points that I believe will help you understand these key differences in order to get the most out of Houdini.

01 Procedures

The biggest difference between Houdini and other 3D software is proceduralism.

According to Your Dictionary, the definition of a procedure is: “A series of small tasks or steps taken to accomplish an end.”

In most other 3D software, scenes are handcrafted by artists by adding elements and refining things manually. It’s like working with clay – time is spent crafting a beautiful end product. The problem with this approach is when the process needs to be repeated or modifications are needed. Often the artist has to repeat the entire process again.

For one-off models this approach is fine, but it’s expensive and time-consuming for many real world production demands, such as scaling up the production of assets or being able to respond quickly to creative changes.

In Houdini’s procedural approach, the scene is described

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in the software as a set of small steps (procedures), which will be performed in a specific order (the process) to create the final product.

Making a scene is like designing a machine by describing the procedures that will be performed during the final process. Only when evaluating the whole, or part of the process is something new created. The advantage of this is that once you evaluate the process, the machine can repeat this and make lots of objects automatically.

By simply varying the parameters of the procedures, variations can be made automatically.

In most 3D software, scenes are designed and then crafted by hand. In Houdini, the system to describe building the scene is designed and subsequently can be run repeatedly.

Understanding the procedures and designing and building the process is essential for getting the most power, the best results and the most fun out of Houdini.

FEATURE

Get to grips with Houdini

Right: Individual nodes and their parameters Below: These parameters live and operate within Houdini’s contexts

02 Nodes and contexts

Inside Houdini, you will find that procedures are defined as nodes. These nodes have parameters that affect the way that the nodes behave. These nodes can be thought of as mini computer programs that simply process the data that is passed through them.

Nodes are the processing power of Houdini, and understanding the features of each one is where the power lies. There are a few nodes that nearly all Houdini operators constantly use, such as the Copy, Scatter and Wrangle nodes, as well as the specialist ones, which are less frequently used.

Houdini has different contexts to do different things, such as

modelling, simulations and even compositing. Each has its own set of nodes and can pass data easily between the other contexts.

Houdini users have their own language which refers to these contexts. For example, it’s not unusual to hear phrases like: ‘Let’s do that in SOPS then take it to DOPS and then back to SOPS for rendering in ROPS!’ Wiring these nodes in networks and sharing data between other networks in other contexts is how an artist can build a powerful procedure to automate large amounts of work.

Now that we know about the procedures, we need to find out about the data they work on.

Houdini’s contexts are: SOPs: surface operators (modelling) DOPs: dynamic operators (simulations) POPs: particle operators (particles) SHOPs: shader operators (materials and shaders) ROPs: render operators (output renders and geometry) VOPs: VEX operators (scripting – this context can be found in all others too) COPs: compositing operators (image manipulation) CHOPs: channel operators (data channels signal processing) MAT: a brand new material context

layout and evaluation 04 Network

Understanding how the node network evaluates is critical in designing efficient processes and fixing issues. The blue display flag on a node is where you start.

Houdini works its way up to the top of the network following the left-hand branch only. Once at the top, this is the first node to be listed for evaluation. Houdini works its

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about attributes on points 03 All

Essentially, everything you do in Houdini boils down to manipulating and storing data on points. This data is referred to as attributes. An essential attribute is ‘P’ for position. Without this attribute, you would not know where the point sits in 3D space.

Other common attributes are for things such as ‘N’ for normal.

Usefully, you can make your own custom attributes, too.

A node processes these attributes as the geometry and is fed through the network. The parameters or channels on a node allow you to vary its behaviour, which will ultimately change the attributes. Since all points have a ‘P’ for position attribute, the simplest thing you can do is have a node change ‘P’ and the point will move. Manipulating attributes is key to most of the work in Houdini.

You can see the attributes on geometry by using the Geometry Spreadsheet panel or by choosing the Spreadsheet option when rightclicking on a node.

way down the network tree listing the nodes and dependencies as it goes. If Houdini reaches a branch on its way down, it will then go back up to the top following the next available left branch and then work its way back down the network again. Once at the bottom, Houdini evaluates the list of nodes to show you the result. Remember that Houdini always evaluates networks from left to right.

FEATURE

Get to grips with Houdini

Expressions show up dark green. Clicking on a parameter name will then toggle between the expression and the result

quick powerful control with wrangle nodes 06 Add

05 Accessing data

Houdini organises its data and nodes like the files and folders of a system such as Windows.

To see this file system, switch to the technical desktop to see the tree view. The tree view is the best way to navigate and understand other people’s networks. The nodes can be thought of as folders and the data as their contents. You can see the paths of the nodes at the top of the network pane.

In expressions, you can access the nodes data or its channels by just using the file path.

For example, to access the size X parameter of the default box

07 Working practice

It is good working practice to pick a consistent colour scheme for your major nodes so that you and others can easily identify them in large networks. As an example, I always colour my ‘data in’ nodes green and my ‘data out’ nodes red.

Pressing [C] in the network pane will bring up the colour palette.

This allows you to colour your

object for a ‘ch’ expression, you should use the path ‘/obj/box_ object1/sizex’. This is in the form of ‘/path to node/parameter’.

You can find out the parameter names for an expression by holding your cursor over the parameter name in the parameter pane window and a pop-up will appear containing the expression name and its description.

For other expressions, you use the file path so that the expression knows which node to operate on.

Houdini will auto-complete your file paths as you write these expressions, which is the same as when working in Linux.

nodes. Select a node then pick a colour from the pallette and voila, your node is a new colour.

In the latest version of Houdini, you can also now change the shape of the node. There are X shapes, circles and even a ‘bone’ shape!

Whichever shapes and colours you choose, remember to be consistent, otherwise when you open your scene at a later date, nothing will make sense.

Node networks can be complex and hard to understand for other people and even for you when you have not opened the scene for a while. You should always label your nodes clearly and take advantage of Houdini’s sticky notes to clearly document the different parts of your networks.

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It is not just the nodes that can process data and change attributes in Houdini. VEX is a high performance expression language in Houdini and this language allows the user to write code to directly manipulate attributes. Wrangle nodes are a quick and really simple way to write small lines of VEX code to read, write and process attributes. Wrangle nodes can be found within all of Houdini’s many contexts.

In a Wrangle node, there is a small down-facing triangle next to the text box. Clicking on this will reveal a menu that has some useful examples of VEX code that you can hack. More examples can be found in the docs.

get going in houdini!

In summary, Houdini is nothing more than a bunch of procedures defined by nodes that manipulate the attributes on points within a file system.

This is essentially all Houdini does – it’s very simple, really, particularly once you grasp the concepts I have outlined. Houdini’s power and the fun of using it comes from seeing the wonderfully complex networks that people can come up with. A great source of example networks can be found in the documentation. You can access these by pressing [F1] on your keyboard and looking in the examples section. You can search for specific nodes and see various examples of their many uses. These scenes are created by the genius team at SideFX, and who better to learn good working practice from than the creators themselves!

If you hold your cursor over a shelf item when pressing [F1], then you will be taken straight to the relevant page in the documentation. This also works for the parameters on some of the older nodes.

The only real way to learn Houdini is to start using it, as well as looking at and learning from other people’s networks and techniques.

So before you start your next project, consider using Houdini. The question is not whether Houdini can do it, but really whether you can do it in Houdini.

Good luck! And more importantly, have fun!

For exclusive demos of Houdini 16 visit The VFX FYI Festival: www.bit.ly/vfx-festival-2017

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Tutorials

Make a bubble in Houdini 16

Creating a realistic, translucent bubble with rainbow effects is easier than ever before with Houdini 16 tools

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Tutorials

Make a bubble in Houdini 16

make floating bubbles with houdini 16 Artists from SideFX share how to make a bubble using Houdini 16 Solid Objects tools

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oudini’s Finite Element Method (FEM) enables you to simulate solid objects as if they have a material inside them. This is great for flexible, fleshy, organic simulations, such as muscles and skin, and can create more dynamic deformations in a simulation by allowing the surface to bend before breaking.

With the new reworked tools and options of the FEM objects and solver in Houdini 16, you can now use these tools in a wider variety of ways.

In this tutorial, David Ertsinian will explain how to push the FEM solids to create a floating organic bubble. The workflow is much less complicated than in Houdini 15.5, and getting the desired look is now just a matter of finding the right parameters.

FEM is perfect for bubbles since Houdini 16 enables you to decide how the inside and outside of the object react separately. The shell options basically act like surface tension for the object. When you have the initial deformations and

the model’s parameters set up, all you need is to add some external velocity in the Drag tab, which behaves like a wind force. With the exception of gravity, no other Surface Operators (SOPs) are needed, as they are built into the solid object.

Joshua Matthews will also review shading in Houdini.

When building a shader, physical accuracy is a great starting point, and a bubble has many aspects to consider. The refractions and reflections, however, have the biggest contribution to the shader.

Houdini 16 also has a new feature called Transmission, which means you can create shaders with dielectric properties, giving the rainbow effect we see in bubbles.

SideFX Houdini

Download your resources For all the assets you need go to www.bit.ly/vault-221-VFX

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Tutorials

Make a bubble in Houdini 16

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part 1: make bubble Create a sphere in the centre of your grid and change the type to Polygon. The simulation won’t work correctly if it doesn’t use triangular polys. Lower the Radius and raise the Frequency slightly so that you can sim quickly.

Attribute Wrangle. You will need the initial rest position and current position so you will have to use the expression. You need this expression when doing simulations that have plastic-like deformations.

In the same wrangle, scale the X, Y and Z values. For example, using the expression v@P.x *= 0.5 for each axis.

02 Hybrid Object Set-up

04 hybrid Object Settings

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Getting Started

Author David Ertsinian David Ertsinian’s goal is to make awesome simulations in films. He’s currently, interning at SideFX in Toronto. www.vimeo.com/ davidertsinian

Create a Solid Conform node and attach it to the sphere. This node helps create inside geometry to be a part of the deformations.

Slightly drop the Max Tet Scale and select Add Surface Triangles. Now you can go to the Solid tool bar at the top and choose Hybrid Object.

Initial Stretching Set-up 03 create

By starting with deformations, you can get nice-looking shapes more quickly than if you were to start with nothing. Create an

Before you change any settings inside the Dopnet, if you play the sim, you will see a sphere growing to a point and then it will stop. Starting in the model options of the Hybrid Object, drop the Stiffness Multiplier of the Shell and Solid settings significantly (for example, using Values between 10-15). Get rid of the Damping Ratio. Lower the Shape Stiffness of both the Shell and Solid. Change the Mass Density of the solid to 1 and raise the Volume Stiffness to 1000.

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05 Collisions and Drag

Collisions are not really needed for this simulation, so in the Finite Element Solver you can turn off Enable Collisions and Fracturing. In the Drag tab, a small amount of Drag should be added so that the warping will slow down.

A value of 0 will keep the warping bubble going forever. The External Velocity Offset is your wind force here. You should use an expression that gives some variation, such as a sin function.

06 Finalising your bubble

Some things to play with are inside the Finite Element Solver. Raising the Substeps and/ or changing the Integrator Type will change the look. When you are happy with your bubble, back in the original Geo node, you can raise the Frequency to get more details, then cache out your sim. On top of that, you can subdivide the cache to try to get even more details.

Tutorials

Make a bubble in Houdini 16

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part 2: SHADING

01The Classic Shader Author Joshua Matthews Joshua Matthews is currently interning at SideFX in Toronto, where he is improving his skills with Houdini each and every day! www.joshuamatthews.com/

In this example, we will be using the Classic Shader, which was previously known as the Mantra Surface. The Classic Shader settings will need to be tweaked to give a proper base for reflections and refractions. I first enabled Coat Reflections to give the illusion of having a reflective layer on top.

Then I enabled Refractions and increased the Intensity to 1.5. After changing these settings, the shader should look like a thin glass.

Dispersion and GGX 02 Using

Dispersion is a parameter in the new Houdini 16 shaders that changes the colour of the refraction based on the frequency of the

02 wavelengths in your lights. This creates the rainbow effect that you see in diamonds or caustics from glasses. This feature is only available with GGX refractions, so be sure to change the refraction model from Phong before rendering.

03 Faux Fresnel

Bubbles tend to have more reflections and distortions around the outer edge of the bubble, while the inside tends to be mostly transparent. This is due to fresnel reflections, which are when a material has two differing indexes of refraction. Opacity Falloff can emulate this effect inexpensively,

and is how I got my bubble to stay transparent on the inside, while maintaining the reflections and refractions on the outside.

04 Curl Noise

To push the bubble’s colours, add Curl Noise to the base colour of the shader to emulate an oily sheen on the surface. Because Curl Noise is a 3D noise, it will translate to RGB when added to the shader. Inside of the Material Network, place a Global Variables, Transform, and Curl Noise vop. Connect the nodes as in image 04 and ensure that the Transform is changing from current to world space.Â

Rendering tip

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For the best rendering results, use an HDRI image in an Environment Light to create nice crisp reflections on your created objects.

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Tutorials

Make a bubble in Houdini 16

master realistic hair in houdini 16 Andrey Belichenko shares how to make the most of Houdini 16’s new set of tools to make fantastic-looking hair

Author

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Andrey Belichenko A 3D and 2D artist, photographer and filmmaker from France, Andrey loves the traditional arts yet believes that new technologies allow artists to perform miracles. www.cgfaunstudio.wixsite. com/home

fter you have spent time creating long and carefully laid-out curly hair, imagine that the director of your project comes and says, “Good hair, but I want it less frizzy with more curls.” In this situation, using most 3D packages, you have to almost completely remake the hair.

In Houdini, if you create a well thought-out process from the start, you can make these changes with a single click later.

Due to its procedural core, Houdini enables you to create a hairstyle very quickly, and you have complete control across all the stages of creation.

Here is my method for creating the hairstyle used for my female character. Such techniques may vary and Houdini enables each artist to come up with their own unique workflow.

Considering the large suite of tools that Houdini already has to offer (for other needs), these tools are very flexible and you can always change them as needed for each of your projects.

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In Houdini 16, the Hair and Fur tools have been heavily reworked.

The process of creating hairstyles is intuitive, even for a novice, and a power user can now do their work faster and concentrate on creative tasks. I find the new hair system very elegantly designed. There is no need to run across the entire network and make changes here and there. Everything you need to create fantastic hair can be done in two or three places.

Download your resources For all the assets you need go to www.bit.ly/vault-218-houdini

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New tools • No blackboxes, unlocked pipeline • Full use of Compiled Blocks • Hair Generate SOP • Direct procedural manipulation of guides’ geometry • Easily override parameters •Interactive grooming via the Guide Groom SOPs • Plus many more!

Tutorials

Make Createa bubble hair with in Houdini 16

good hair day Create flowing locks using Houdini 16’s improved Hair and Fur tools SideFX Houdini

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Tutorials

Master hair with Houdini 16

a procedural spiral and set form 01create

I create a procedural spiral. The input is a base curve, where I draw the trajectory of the curl strand: 3-5 points in this curve is usually sufficient. In the parameters of the spiral, I set up the form: the number of rotations, amplitude variation along the curl, and so on.

By changing the shape of the curve, I change the trajectory of motion of the curl and still retain the spiral form settings. Image 01 shows the guides displayed after a polywire (this is for visualisation only). The Hair Tools only generate curves.

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adjust curve shapes

If I want to bend a strand of hair to the other side, I only need to move 1 or 2 points on the initial curve (curve 109, 110, 111). If I want to change the curl amplitude to have a little less at the start of the curve and then a bit more at the end, I just move 1 or 2 points on the amplitude ramp. Any of these parameters can be animated, thus providing unlimited possibilities in animating the hairstyle of your character. Also, my spiral asset (helix_for_hair) has a handy colour ramp, which I will talk about later.

For now, it can be split by the colour of the hair strands to make it easy to identify – a really convenient feature that speeds things up.

03 organise network

I add hair to a separate geometry (scalp). This provides an additional option for control. I create the scalp using TopoBuild and apply a UV Project on it. I then create a hair guide starting from the bottom base to the top, so that it is easier to access. You can see the

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02 Guide curves Draw guide curves instead of using Add Fur. Then copy/paste that curve into your network as guide curves, and make slight changes until you’re totally satisfied.

layout of it in my network in image 03. Now, if I need to, I can control each and every guide.

04 control the hair

Use the control settings on the scalp‘s hair – play with the options for custom guides, options for width and thickness, and

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clumping with amount of influence.

Use the ramp to set points to control the amount of tightness of clumping along the guide curve.

05 enable dynamics

It is important to check the hair in simulation – so your hairstyle will change and respond

Tutorials

Master hair with Houdini 16

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07 to things such as gravity. If you don’t do this, you risk having a beautiful hairstyle for static images, but poor dynamics. Your hair may either be too hard (as though you’ve used a lot of hairspray) or you outright lose the shape quickly within the first few frames.

Dynamics settings for different hair length will vary. Download image 05 from the Vault for my settings.

06 adjust rigidity

I use the red colour channel to make the hair more rigid in some places. In image 06 you can see where there is less red the hairstyle is more mobile, and where there is more red, the hairstyle holds its shape fully. Red is easy to visually monitor and you can also transfer this atttribute into @kangular and @klinear (angular spring and linear spring, which affect the bending of wires and curves in Houdini).

Seeing red If necessary, reduce the red colour on guides.

You can make it red over the entire length of the guide or have it on the tips only – this depends on the task at hand! Also, don’t forget to look into Houdini help (docs), where you’ll find the answers to all your Houdini questions.

thickness to each guide 07 assign

The thickness is done via the hair guide, so you can assign a thickness to each guide separately and even make it cone-shaped. If you need a similar effect, for example to create blades of grass, you can modify any attribute of any hair setting this way.

08 SideFX Houdini

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clumping tightness 08 adjust

In some areas, I need to change the clumping tightness. I paint a custom attribute and add or subtract it from the @tightness attribute. Overall, you can create customisable and varying clumping tightness per clump across your entire hair gen.

Tutorials

Master hair with Houdini 16

09 shade hair

The appearance of the hair depends largely on the shader. The default Hair Shader does the job for me, as you can see from my settings in image 09 (downloadable from the Vault). To randomise more hair colouring along the length of the hair, I add two more colour ramps.

One adds colour wherever I want it, and the other subtracts. Different noises for added variety of colour are then added in from COPs (Compositing Network).

10 add real-life details

Usually, in real life, there are hair strands that stray slightly from the bulk mass of the hair. To reproduce this effect, I add frizz to it; the trick is not to add it to all the hair, but only to a small percentage of it. This percentage is then controlled by noise from COPs (see more on this below). My settings are shown in image 10. I do the same for length randomisation.

looking results. Several guides need to be corrected like this. I add frizz and a wave at the top of the head.

11 recursive clumping

12 guidegroom node

I use Recursive Clumping. I love this new workflow as it gives me a high degree of control by being able to layer and blend clumping values together to get natural-

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For the final touch, I use a GuideGroom node to do the final styling and adjustments, such as digitally combing the hair and adjusting each guide strand.

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Watch out!

If you change the hair length or amplitude of a curl, the settings for Dynamics will have changed. All settings for Dynamics and hairstyle are interdependent.

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13 set cops network

My COPs network looks like image 13. Now, if your director comes to ask you to change a little bit here and there, or when in the next episode of the film your character’s hairstyle has to be curlier, you can very quickly make the necessary changes. And this is only possible using Houdini!Â

A devilishly good 3D procedural platform.

Start learning today with Houdini Apprentice – a FREE version of the same software used by the world’s top film, TV and game dev studios. Visit SideFX.com today.

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Creature artwork: Tanvir Islam