houdini

Houdini

nebulae in houdini

I’ve been very, very busy, which is a lame excuse for the lack of posting new things, but there you have it.

Much of my work time recently has been dedicated to building inky, nebula-like effects in Houdini. Generally speaking, when you’re trying to make that whole ink-in-water effect, you dust off your copy of 3DS Max, do a quick fluid simulation, advect a bunch of particles through it, and then cache out a bazillion partitions of your simulation with different random seeds, then render in Krakatoa. Well, I have none of those things, and I needed greater control over the simulation than what can typically be achieved in Fume/Krakatoa, so I tried to do it in Houdini. I definitely have a lot of respect for the Krakatoa renderer after a week spent on this effect. This stuff is hard! Hit the jump to see exactly how I went about this…

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By toadstorm, ago
Houdini

Nesting L-systems in Houdini

L-systems can get very complex very quickly. If you want full control over exactly how the plant grows and what its final shape looks like, you’re in for a long haul. There are a few ways to get “artistic” control over an L-system, like using metaballs to influence rules depending on the turtle’s position inside or outside the volume, but in general a single L-system has to control everything just with variables, which gets tedious quickly. It gets even worse when you want complex branching structures.

I was following along with the excellent L-systems tutorial (part 2) from cmiVFX, which offers a way to nest L-systems using some creative use of the Copy SOP. If you’ve checked out the tutorial, it’s in an older version of Houdini which historically crashed when you tried to connect L-systems together as Leaf inputs. While this isn’t the case anymore with Houdini 12, you still miss out on the big advantage of the Copy SOP method, which is manipulating point attributes and using these to set properties of the branch L-system using copy stamping.

I won’t go into the finer details of setting up this method; you really should just watch the tutorial I linked to in order to understand how the Copy SOP method of nesting L-systems works. Basically there is a “trunk” L-system, which has rules that call for a “J” leaf. The “J” leaf receives a simple curve with three points, one at the center, another straight above the center (+Y), and another along the positive Z axis. After this curve is copied onto all the J inputs in the L-system, you can use the difference in position of these points relative to each other to determine a normal and up vector for each instance of the curve, and write these vectors to the points. Then the points other than the center points are deleted, along with the trunk, leaving you with a bunch of points from which branches will sprout, each with attributes N and up. These attributes are automatically used by the Copy SOP to orient an instance of a second “branch” L-system to each point. Again, this is a very quick write-up of a complex network, and you should watch the tutorial. Hit the jump for more…

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By toadstorm, ago
Houdini

Some notes about L-systems in Houdini.

I’ve been spending a good amount of time recently on trying to figure out L-systems in Houdini. I’ve always wanted to be able to grow plants in 3D, and I was always frustrated by the lack of flexibility in Maya’s Paint Effects and the Onyx plant generator, so I figured it was time to learn this once and for all. Let’s just say there is a bit of a learning curve, like anything else in Houdini.

I’m not going to go into the basics of L-systems here, there is way too much for me to even consider posting. The best resources I’m aware of for learning how to use them in Houdini are this tutorial on Digital Tutors, and this tutorial on CmiVFX. The Digital Tutors tutorial is probably a little bit easier to start off with as it tries to take a more flexible approach to making the plants grow (as opposed to CmiVFX’s more “pure” L-systems approach) but they both require basic Houdini ability before you start.

Anyways. The plant I was trying to create was a little seedling, with leaves that unfurl as they grow out from the main stem. Here’s what I came up with:

Hit the jump to see the breakdown…
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By toadstorm, ago
Houdini

motion trails in houdini, part 3

Okay, now for the last part of this tutorial: We’re going to turn the motion trails effect into a Digital Asset, which a single node with inputs, outputs and parameters (just like any other node) that can be shared with other artists. The network we made to create the effect is big and ugly, and no one in their right mind would want to copy and paste that whole thing from scene to scene and start jumping across the SOP and CHOP networks and look for individual nodes to tweak parameters. Digital Assets let us package everything together nicely.

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By toadstorm, ago
Houdini

motion trails in houdini, part 2

Now that the initial trails setup is done, it’s time to get the audio effect in there. CHOPs in Houdini (channel operators) are really, really powerful, but they’re often the last part of the program that anyone touches. They can turn simple motion and effects into much, much more complex effects pretty easily. I still am unaware of the vast majority of things you can do with CHOPs, but I hope this example will be a good start for anyone who’s trying to learn Houdini…

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By toadstorm, ago
Houdini

motion trails in houdini, part 1

I haven’t posted in a long time mostly because I’ve been spending the majority of the last month devouring Houdini tutorials on the internet. Houdini is capable of handling incredibly complex visual effects, and its node-based architecture makes it ideal for effects R&D… if you can get past the learning curve. I’ve never seen a more complicated-looking program.

Anyways, after beating my head against the wall for the better part of a month I’ve finally started making sense out of this program, and I want to share an effect I’ve been researching for an upcoming spot, and turn this into a sort of tutorial for dealing with particle systems, creating objects on the fly, and manipulating shapes using audio. Later on I’ll also go over how to make the effect into a “digital asset,” meaning packaging the effect into a single node with its own interface that you can then use for other shots or share with other artists.

I really dislike video tutorials so I’m going to try to write this one out. The first segment will be about creating the trails, the second will be about modifying the trails using CHOPs, and the third will be about repackaging the effect as a digital asset and building an interface.

Anyways, here’s the effect we’re creating:

I realize it kind of all turns to spaghetti in the end, but that could probably be fixed with a little more fine-tuning, and I wanted to show a little complexity to the effect. Hit the jump for a big huge post about how this is done.

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By toadstorm, ago