My latest gigantic Houdini project is finally live! I was the Technical Director for this one, which also means Houdini tube effects, lighting, shading, rendering, etc. Thanks to my fellow Houdini artist, Alvaro Segura, for handling the inky effects, as Read more…
Many operations in Maya will run faster if Maya doesn’t have to refresh the viewport while running them. For example, if you switch the viewport to only show the Graph Editor before baking animation, or caching particles or Alembic geometry, the operation will happen much faster than if Maya had to actually display the geometry for each frame that it’s being baked. There is probably a way via the API to tell Maya’s viewport not to refresh, but since I don’t know shit about the API, here’s a workaround using a few of Maya’s less-documented MEL commands and some Python.
I wrote this method assuming that artists would want to cache out information frequently without it disrupting their workflow. That means that I needed to first store the user’s current panel layout, then switch it to something that doesn’t require a refresh on every frame (like the Graph Editor), and then restore the previously restored layout.
I prefer coding in Python, but some of the procedures I’m running are MEL functions that are found in scripts/startup and so they’re not documented and they don’t have Python equivalents. A hybrid approach is the best way to handle it, since MEL is terrible.
Click for some Python code… (more…)
Just wanted to document a dumb little problem I was having. My compositors need cameras in .FBX format, and I had a camera that had a Look At object (an aim vector) which wasn’t being considered in the export. I Read more…
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…
A short film that I worked on with a friend of mine, director Dan Blank, is finally out to the public! I was the CG Supervisor, and I handled all of the lighting, materials and rendering in addition to the Read more…
I’m working on a project right now that involves exporting cached geometry from Houdini to Maya. The Alembic node makes that a fairly painless process now that Houdini and Maya both support Alembic import/export, although it turns out that getting Read more…
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…
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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I just ran into a hideous problem when I was trying to bake out cameras and animation from one scene, and get the animation into another. I always keep my lighting scenes separate from the animators’ scenes so they can’t mess up my shots. Unfortunately, the animator had used a Scene Time Warp, and then baked out the animation, which of course never quite lined up correctly and we couldn’t figure out what was going on. Turns out that keys baked under a Time Warp will not actually bake the Time Warp itself.
Here’s a script, then, to bake the effects of the time warp on all selected objects. It then (optional, but recommended) deletes the time warp from the scene entirely:
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.