Building procedural game assets with Houdini

In theory, COPs could replace Substance Designer and be even more powerful, because you have full access to other Houdini networks and your 3D data. You could use it to generate texture details based on geometry and even other adjacent objects in the scene. Unfortunately COPs are slow – very slow. Most of advanced texturing work is done via COP VOPs and when working in that context – as soon as you modify or add new node – Houdini recompiles everything and re-cooks your COP network. While doing that, it becomes unresponsive for quite a long time, making working with it quite unpleasant endeavor.  Before telling how I scrapped the idea of using COPs and did everything in Substance Desinger, I will first quickly explain basic COPs workflow – because it is still useful for a lot of cool tricks – for example in baking  some sort of custom utility texture that you will use later in game engine.

Because COPs were too slow, I decided to use Substance Designer to generate my textures. SD is almost like and industry standard, so it seemed a reasonable choice for texturing pipeline.
Because Substance Designer ir strictly 2D procedural texturing tool, you don’t have access to 3d geometry. Therefore all the data you need should be baked in textures beforehand.

Generating textures in SD was a bit tricky. Because I wanted to generate unique geometry based textures for each 3D asset, it means I needed to work in 3D space and convert to 2D texture space at the end. This way all generated texture details would be orientated correctly even if UV island is rotated. And most importantly – this way you can eliminate seams between UV islands.  Easiest way to do this is to do everything with triplanar mapping. When doing triplanar, one thing is that you can’t use Normal maps directly as they are tangent space dependent. Easiest way to solve this is by not using them at all, but using only height maps which I then convert to normal maps after triplanar projections. Of course this is not a real solution – especially if you don’t have height map info available and must use intricate normal maps. But for most surface details, it gives good enough results. To be fair – in most substances out there, they are usually built by first producing a height map and generating normal map from it internaly. Usually you can ignore the normal map and reference the height map directly and convert it to normal map yourself after triplanar mapping and get the same quality normal map. So it works fine for almost any existing substance out there that you might want to use in your texturing workflow.

After generating the normal map, I then combine it with a baked normal map from high poly geometry to get final normal map.

As for texturing itself – I used ready made sandstone and rock substances from Substance Source and I blended them using procedural masks generated based on input (baked) textures. Output textures in this case are specificaly made for Unity engines HD render pipeline.

Once my substance file is set up – with proper input and output nodes, I can use Substance Automation Toolkit sbsrender command line tool to render out final textures. You give it path to substance archive you want to render, specify substance name inside the archive, specify all input parameter values (paths to input textures, numeric values etc.), set the output resolution and finally specify output texture paths. This can easily be integrated in Houdini PDG using Python TOP node. This way I can automate unique texture generation for each asset if needed. More on this in the next part of the article!