Learning Houdini Journal 07: Materials

Dec 13, 2015 at 01:16 am by -gToon

This is the seventh entry of what will be a year-long journal on learning the 3D application Houdini, created bySide Effects Software. Houdini is a sophisticated application that is widely used in the production of visual effects for Hollywood films such as Big Hero 6, Mad Max: Fury Road and many others.

In my previous Learning Houdini Journal 6, I talked about learning Polygonal modeling via the PluralsightIntroduction to Houdini course taught by John Moncrief. I also discussed using "Expressions" in Houdini 15 Apprentice and covered why the procedural workflow that Houdini offers is so unique and useful.

I was a bit too ambitious in thinking I could finish the Introduction to Houdini 15 course this week. I spent most of my time learning materials and shaders in Houdini, which, like everything else in this great application, has a logic and a process all its own. I won't go into detail on this as it would take pages and pages of descriptions, but I can give a general idea of materials in Houdini 15.

Houdini creates special networks in the application which cover specific operations (like materials). Each section is an "operation" on a particular task. Materials/Shaders are the Shop are (Shader + operation). Other areas are Sops (surface operators), Dops (Dynamic operators) and Rops (Rendering operators), along with many more.

All materials applied to model

In working with materials in Houdini, I learned how to create groups that the materials will be applied to on the model. You select the areas using the brush mode selection, then create the group. Houdini has a few special ways of creating groups by using procedural nodes and then adding/subtracting based on the groups selected. I basically followed along with the instructor in creating the groups for the wheel I modeled. The rubber tire, the chrome inner area and the wheel/brake assembly. Once I understood the process, it became very clear to me.

One thing that slowed me down a bit was that I didn't realize you had to add the specific material from the materials palette to the XX in order for it to be available in the Shops network. This sounds a bit complicated, but it wasn't once I understood what the problem was. Thankfully, the course materials were provided with the Introduction course at Pluralsight, so I downloaded the scene file lesson 30 and opened it up. This was when I realized that the materials need to be transferred first. You can't just drop material into the specific group.

I also realized that the course provides ALL of the scene files for each lesson and that I had been using the same scene file from lesson 9 up to this point. Now I know better and will open each scene file for the specific lesson I'm working on.

Materials palette
Materials palette for the sports car scene before tweaking

Pre-created Material Groups
The imported sports car came with groups already created by the artist. They were logical (body, under the car, lights, windshield, etc.) but the instructor wisely chose to combine two of the groups because they would have the same material applied to them (in this case the lights and the windows would get the glass material), so he took me through the process of combining groups which was quite easy and intuitive in Houdini 15.

I suspect this won't be a problem when I model everything from scratch for future projects, but it was good to see how this works in a pipe-line situation where someone else might model part of your scene for you

First Crash
I don't quite remember what I was doing (I probably should have noted it and posted it as a bug) when I experienced my first crash in Houdini 15. The program has been like a rock for 6 weeks now, so I'm not worried about stability in this application. My habit from using other applications is to save every 10 minutes which helped me out as I only lost a small amount of work which was easily re-created. Next time, I'll note what I was doing and report it to the bug forum at Sidefx.com.

The Materials Palette
I'm a little surprised at the seeming dearth of materials in the materials palette in Houdini 15. In other applications, you get a huge collection of materials. But perhaps this is only my lack of knowledge and experience with Houdini. Perhaps you get basic materials and then spend a lot of time adjusting them and then finally saving them as an additional material in the palette? We'll see how this turns out because the next lesson I start on for next week is refining the materials for the car and the wheels.

I think I'll also do some reading in the manual and take a look at some of the tutorials at sidefx.com for more info.

Next: Refining and Tweaking Selected Materials in Houdini 15

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