PIPELINE TECHNIQUES: essential Houdini tips for the new user
Tyler Bay’s friendly beginner’s guide
Houdini is one of the most impressive, well-built 3D applications on the market, and there’s nothing else quite like it. When somebody mentions Houdini the first thing that might come to mind is incredible VFX! Procedural workflows!
And… it’s also perhaps an application that’s super intimidating and almost impossible to learn at first. For many people, Houdini looks like something that’s a bit too out-of-reach or technical, but in my opinion, it’s actually quite easy to use once you get past some of the basics. When I set out to create the Houdini For The New Artist course I wanted to make Houdini as friendly as possible to the artist, build something that looks awesome, and offer a way to eventually reach harder concepts with a foundation of skills and knowledge set in the right place. Let’s take a quick look at how that can happen with this tutorial. The goal here is to create a transformation effect that turns a dark-marbled dragon into gold by using a combination of particles and custom shaders.
Also, as a side note, be sure to check out the Filesilo as you’ll find extra resources, such as a Houdini cheatsheet, designed specifically with the new user in mind.
01 Prepare the scanned model The first step in this process is to prepare the dragon model. When working with scanned models, it’s important to reduce the poly-count so that our scene doesn’t get too slow. To do this, we can use the Poly-reduce node and set the target poly-count to 100,000. On top of that, we’re also able to paint areas that will contain a higher concentration of those 100,000 along the face to preserve some of the important, fine details where it matters.
02 Texture in Substance Since the typology is dense and triangulated, the best way to apply UVS is by selecting miscellaneous sections of the mesh and unfolding them. In order to do this, you can either select the faces manually or use the Auto-uv node that can be found within the game-dev toolset. Next, go into Substance Painter, here I utilised Substance Source for the base marble material along with the gold and then I baked out all the usual signal maps like occlusion, edges and so on. After adding some dirt, oxidation and other details, I also made a mask that will be used to control where the particles will eventually spawn.
03 Apply the texture maps To bring all this back into Houdini, you can set the export style within substance to Metallic/roughness along with switching the Normal map style to Opengl. This setup works well with Houdini’s principled shader, and all the maps just get read directly into the material parameters.
This setup works well with Houdini’s principled shader, and all the maps just get read directly into the material parameters
04 Set the key light Next is lighting! The first thing I start with is an overcast, blue-coloured HDR that’s set to a low exposure. By doing this, my goal is to allow the light values to hover just above black. This adds detail to the shadowed areas and gives us a base to work off of. After that, I begin setting the key light.
When adding this, I try to imagine what the light is doing to the personality of the face. I could make the dragon feel heroic or menacing just by the angle, so I went for a heroic feel by setting it to the top-left position.
05 Add rims, fills and ‘skimmers’ Once the key light is in place, I move on by adding other sorts of light such as rim lights, fills and something I like to call ‘skimmers’. Rims help define the silhouette. Fills help in recovering form that gets lost in dark areas and ‘skimmers’ skim the surface to pick up the small details that can be found along the surface.
06 Apply interesting forces On top of this, extra forces get added to the Solver to help control the general behaviour along with adding break-up and variation.
For this, I added a Wind Force to help give a wavy behaviour along with some noise that pushed these particles in various directions.
07 Using noise to mask gold Once the DOP network is set up, the next step is to create a custom shader that will blend between the dark marble and gold materials. To do this, first create the two principled materials independently from each other. After this, you can simply blend the two by using a Layer Mix node.
To make this work though, the Layer Mix needs a way to read the surface of the geometry and either say ‘yes, this is gold’ or ‘no, this is not gold’. We can tell the Layer Mix this information by using attributes.
08 Use attributes for more control An attribute is basically like a piece of information that gets attached to our geometry, and in Houdini, setting and creating your own custom attributes is really easy. For this gold effect, I used a noise to assign a Yes value of 1 or a No value of 0 along the surface of the geometry. As the noise animates over time, so too does the location of the gold vs marble, and I can plug in all that information with a custom attribute into the Layer Mix node in order to make everything work. I also used this attribute to prevent particles from spawning wherever there was gold.
To do this, first create the two principled materials independently from each other. After this, you can simply blend the two by using a Layer Mix node. To make this work though, the Layer Mix needs a way to read the surface of the geometry and either say ‘yes, this is gold’ or ‘no, this is not gold’
09 Separate elements for rendering For rendering, I separated out each part of our scene – the dragon, backdrop, particles and even the light that gets generated from the particles, into separate renders.
The idea behind this is to optimise render settings for each element individually and then eventually bring them back together in comp.
10 De-grain specific passes Another cool thing you can do with Houdini besides separating out scene elements, is adding render passes.
During comp, we can use these extra render passes to re-build the final image, and along the way, de-grain specific passes that appear too noisy. The cool thing about applying the de-grain effect to specific passes is that this also minimises the negative impact of the de-grain operation. The end result looks much cleaner this way.
11 Composite the final adjustments Last, but not least, all the final compositing adjustments are made. I can control the intensity of the lights even after things have been rendered, add a little bit of glow to the particles, and also fix any areas along the highlights that may have been getting too bright. The end result is what you see here!
Tyler Bay tylerbay3d.comBioTyler Bay is a 3D artist who freelances and teaches online courses. Past projects include Pixar’s Coco along with the Houdini For The New Artist courses at cgcircuit.com.